perf/x86/intel/pt: Fix KVM warning due to doing rdmsr() before the CPUID test

[deliverable/linux.git] / arch / x86 / kernel / cpu / perf_event_intel_pt.c

/*
 * Intel(R) Processor Trace PMU driver for perf
 * Copyright (c) 2013-2014, Intel Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * Intel PT is specified in the Intel Architecture Instruction Set Extensions
 * Programming Reference:
 * http://software.intel.com/en-us/intel-isa-extensions
 */

#undef DEBUG

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/types.h>
#include <linux/slab.h>
#include <linux/device.h>

#include <asm/perf_event.h>
#include <asm/insn.h>
#include <asm/io.h>

#include "perf_event.h"
#include "intel_pt.h"

static DEFINE_PER_CPU(struct pt, pt_ctx);

static struct pt_pmu pt_pmu;

enum cpuid_regs {
        CR_EAX = 0,
        CR_ECX,
        CR_EDX,
        CR_EBX
};

/*
 * Capabilities of Intel PT hardware, such as number of address bits or
 * supported output schemes, are cached and exported to userspace as "caps"
 * attribute group of pt pmu device
 * (/sys/bus/event_source/devices/intel_pt/caps/) so that userspace can store
 * relevant bits together with intel_pt traces.
 *
 * These are necessary for both trace decoding (payloads_lip, contains address
 * width encoded in IP-related packets), and event configuration (bitmasks with
 * permitted values for certain bit fields).
 */
#define PT_CAP(_n, _l, _r, _m)                                          \
        [PT_CAP_ ## _n] = { .name = __stringify(_n), .leaf = _l,        \
                            .reg = _r, .mask = _m }

static struct pt_cap_desc {
        const char      *name;
        u32             leaf;
        u8              reg;
        u32             mask;
} pt_caps[] = {
        PT_CAP(max_subleaf,             0, CR_EAX, 0xffffffff),
        PT_CAP(cr3_filtering,           0, CR_EBX, BIT(0)),
        PT_CAP(psb_cyc,                 0, CR_EBX, BIT(1)),
        PT_CAP(mtc,                     0, CR_EBX, BIT(3)),
        PT_CAP(topa_output,             0, CR_ECX, BIT(0)),
        PT_CAP(topa_multiple_entries,   0, CR_ECX, BIT(1)),
        PT_CAP(single_range_output,     0, CR_ECX, BIT(2)),
        PT_CAP(payloads_lip,            0, CR_ECX, BIT(31)),
        PT_CAP(mtc_periods,             1, CR_EAX, 0xffff0000),
        PT_CAP(cycle_thresholds,        1, CR_EBX, 0xffff),
        PT_CAP(psb_periods,             1, CR_EBX, 0xffff0000),
};

static u32 pt_cap_get(enum pt_capabilities cap)
{
        struct pt_cap_desc *cd = &pt_caps[cap];
        u32 c = pt_pmu.caps[cd->leaf * PT_CPUID_REGS_NUM + cd->reg];
        unsigned int shift = __ffs(cd->mask);

        return (c & cd->mask) >> shift;
}

static ssize_t pt_cap_show(struct device *cdev,
                           struct device_attribute *attr,
                           char *buf)
{
        struct dev_ext_attribute *ea =
                container_of(attr, struct dev_ext_attribute, attr);
        enum pt_capabilities cap = (long)ea->var;

        return snprintf(buf, PAGE_SIZE, "%x\n", pt_cap_get(cap));
}

static struct attribute_group pt_cap_group = {
        .name   = "caps",
};

PMU_FORMAT_ATTR(cyc,            "config:1"      );
PMU_FORMAT_ATTR(mtc,            "config:9"      );
PMU_FORMAT_ATTR(tsc,            "config:10"     );
PMU_FORMAT_ATTR(noretcomp,      "config:11"     );
PMU_FORMAT_ATTR(mtc_period,     "config:14-17"  );
PMU_FORMAT_ATTR(cyc_thresh,     "config:19-22"  );
PMU_FORMAT_ATTR(psb_period,     "config:24-27"  );

static struct attribute *pt_formats_attr[] = {
        &format_attr_cyc.attr,
        &format_attr_mtc.attr,
        &format_attr_tsc.attr,
        &format_attr_noretcomp.attr,
        &format_attr_mtc_period.attr,
        &format_attr_cyc_thresh.attr,
        &format_attr_psb_period.attr,
        NULL,
};

static struct attribute_group pt_format_group = {
        .name   = "format",
        .attrs  = pt_formats_attr,
};

static const struct attribute_group *pt_attr_groups[] = {
        &pt_cap_group,
        &pt_format_group,
        NULL,
};

static int __init pt_pmu_hw_init(void)
{
        struct dev_ext_attribute *de_attrs;
        struct attribute **attrs;
        size_t size;
        int ret;
        long i;

        attrs = NULL;

        for (i = 0; i < PT_CPUID_LEAVES; i++) {
                cpuid_count(20, i,
                            &pt_pmu.caps[CR_EAX + i*PT_CPUID_REGS_NUM],
                            &pt_pmu.caps[CR_EBX + i*PT_CPUID_REGS_NUM],
                            &pt_pmu.caps[CR_ECX + i*PT_CPUID_REGS_NUM],
                            &pt_pmu.caps[CR_EDX + i*PT_CPUID_REGS_NUM]);
        }

        ret = -ENOMEM;
        size = sizeof(struct attribute *) * (ARRAY_SIZE(pt_caps)+1);
        attrs = kzalloc(size, GFP_KERNEL);
        if (!attrs)
                goto fail;

        size = sizeof(struct dev_ext_attribute) * (ARRAY_SIZE(pt_caps)+1);
        de_attrs = kzalloc(size, GFP_KERNEL);
        if (!de_attrs)
                goto fail;

        for (i = 0; i < ARRAY_SIZE(pt_caps); i++) {
                struct dev_ext_attribute *de_attr = de_attrs + i;

                de_attr->attr.attr.name = pt_caps[i].name;

                sysfs_attr_init(&de_attr->attr.attr);

                de_attr->attr.attr.mode         = S_IRUGO;
                de_attr->attr.show              = pt_cap_show;
                de_attr->var                    = (void *)i;

                attrs[i] = &de_attr->attr.attr;
        }

        pt_cap_group.attrs = attrs;

        return 0;

fail:
        kfree(attrs);

        return ret;
}

#define RTIT_CTL_CYC_PSB (RTIT_CTL_CYCLEACC     | \
                          RTIT_CTL_CYC_THRESH   | \
                          RTIT_CTL_PSB_FREQ)

#define RTIT_CTL_MTC    (RTIT_CTL_MTC_EN        | \
                         RTIT_CTL_MTC_RANGE)

#define PT_CONFIG_MASK (RTIT_CTL_TSC_EN         | \
                        RTIT_CTL_DISRETC        | \
                        RTIT_CTL_CYC_PSB        | \
                        RTIT_CTL_MTC)

static bool pt_event_valid(struct perf_event *event)
{
        u64 config = event->attr.config;
        u64 allowed, requested;

        if ((config & PT_CONFIG_MASK) != config)
                return false;

        if (config & RTIT_CTL_CYC_PSB) {
                if (!pt_cap_get(PT_CAP_psb_cyc))
                        return false;

                allowed = pt_cap_get(PT_CAP_psb_periods);
                requested = (config & RTIT_CTL_PSB_FREQ) >>
                        RTIT_CTL_PSB_FREQ_OFFSET;
                if (requested && (!(allowed & BIT(requested))))
                        return false;

                allowed = pt_cap_get(PT_CAP_cycle_thresholds);
                requested = (config & RTIT_CTL_CYC_THRESH) >>
                        RTIT_CTL_CYC_THRESH_OFFSET;
                if (requested && (!(allowed & BIT(requested))))
                        return false;
        }

        if (config & RTIT_CTL_MTC) {
                /*
                 * In the unlikely case that CPUID lists valid mtc periods,
                 * but not the mtc capability, drop out here.
                 *
                 * Spec says that setting mtc period bits while mtc bit in
                 * CPUID is 0 will #GP, so better safe than sorry.
                 */
                if (!pt_cap_get(PT_CAP_mtc))
                        return false;

                allowed = pt_cap_get(PT_CAP_mtc_periods);
                if (!allowed)
                        return false;

                requested = (config & RTIT_CTL_MTC_RANGE) >>
                        RTIT_CTL_MTC_RANGE_OFFSET;

                if (!(allowed & BIT(requested)))
                        return false;
        }

        return true;
}

/*
 * PT configuration helpers
 * These all are cpu affine and operate on a local PT
 */

static void pt_config(struct perf_event *event)
{
        u64 reg;

        if (!event->hw.itrace_started) {
                event->hw.itrace_started = 1;
                wrmsrl(MSR_IA32_RTIT_STATUS, 0);
        }

        reg = RTIT_CTL_TOPA | RTIT_CTL_BRANCH_EN | RTIT_CTL_TRACEEN;

        if (!event->attr.exclude_kernel)
                reg |= RTIT_CTL_OS;
        if (!event->attr.exclude_user)
                reg |= RTIT_CTL_USR;

        reg |= (event->attr.config & PT_CONFIG_MASK);

        wrmsrl(MSR_IA32_RTIT_CTL, reg);
}

static void pt_config_start(bool start)
{
        u64 ctl;

        rdmsrl(MSR_IA32_RTIT_CTL, ctl);
        if (start)
                ctl |= RTIT_CTL_TRACEEN;
        else
                ctl &= ~RTIT_CTL_TRACEEN;
        wrmsrl(MSR_IA32_RTIT_CTL, ctl);

        /*
         * A wrmsr that disables trace generation serializes other PT
         * registers and causes all data packets to be written to memory,
         * but a fence is required for the data to become globally visible.
         *
         * The below WMB, separating data store and aux_head store matches
         * the consumer's RMB that separates aux_head load and data load.
         */
        if (!start)
                wmb();
}

static void pt_config_buffer(void *buf, unsigned int topa_idx,
                             unsigned int output_off)
{
        u64 reg;

        wrmsrl(MSR_IA32_RTIT_OUTPUT_BASE, virt_to_phys(buf));

        reg = 0x7f | ((u64)topa_idx << 7) | ((u64)output_off << 32);

        wrmsrl(MSR_IA32_RTIT_OUTPUT_MASK, reg);
}

/*
 * Keep ToPA table-related metadata on the same page as the actual table,
 * taking up a few words from the top
 */

#define TENTS_PER_PAGE (((PAGE_SIZE - 40) / sizeof(struct topa_entry)) - 1)

/**
 * struct topa - page-sized ToPA table with metadata at the top
 * @table:      actual ToPA table entries, as understood by PT hardware
 * @list:       linkage to struct pt_buffer's list of tables
 * @phys:       physical address of this page
 * @offset:     offset of the first entry in this table in the buffer
 * @size:       total size of all entries in this table
 * @last:       index of the last initialized entry in this table
 */
struct topa {
        struct topa_entry       table[TENTS_PER_PAGE];
        struct list_head        list;
        u64                     phys;
        u64                     offset;
        size_t                  size;
        int                     last;
};

/* make -1 stand for the last table entry */
#define TOPA_ENTRY(t, i) ((i) == -1 ? &(t)->table[(t)->last] : &(t)->table[(i)])

/**
 * topa_alloc() - allocate page-sized ToPA table
 * @cpu:        CPU on which to allocate.
 * @gfp:        Allocation flags.
 *
 * Return:      On success, return the pointer to ToPA table page.
 */
static struct topa *topa_alloc(int cpu, gfp_t gfp)
{
        int node = cpu_to_node(cpu);
        struct topa *topa;
        struct page *p;

        p = alloc_pages_node(node, gfp | __GFP_ZERO, 0);
        if (!p)
                return NULL;

        topa = page_address(p);
        topa->last = 0;
        topa->phys = page_to_phys(p);

        /*
         * In case of singe-entry ToPA, always put the self-referencing END
         * link as the 2nd entry in the table
         */
        if (!pt_cap_get(PT_CAP_topa_multiple_entries)) {
                TOPA_ENTRY(topa, 1)->base = topa->phys >> TOPA_SHIFT;
                TOPA_ENTRY(topa, 1)->end = 1;
        }

        return topa;
}

/**
 * topa_free() - free a page-sized ToPA table
 * @topa:       Table to deallocate.
 */
static void topa_free(struct topa *topa)
{
        free_page((unsigned long)topa);
}

/**
 * topa_insert_table() - insert a ToPA table into a buffer
 * @buf:         PT buffer that's being extended.
 * @topa:        New topa table to be inserted.
 *
 * If it's the first table in this buffer, set up buffer's pointers
 * accordingly; otherwise, add a END=1 link entry to @topa to the current
 * "last" table and adjust the last table pointer to @topa.
 */
static void topa_insert_table(struct pt_buffer *buf, struct topa *topa)
{
        struct topa *last = buf->last;

        list_add_tail(&topa->list, &buf->tables);

        if (!buf->first) {
                buf->first = buf->last = buf->cur = topa;
                return;
        }

        topa->offset = last->offset + last->size;
        buf->last = topa;

        if (!pt_cap_get(PT_CAP_topa_multiple_entries))
                return;

        BUG_ON(last->last != TENTS_PER_PAGE - 1);

        TOPA_ENTRY(last, -1)->base = topa->phys >> TOPA_SHIFT;
        TOPA_ENTRY(last, -1)->end = 1;
}

/**
 * topa_table_full() - check if a ToPA table is filled up
 * @topa:       ToPA table.
 */
static bool topa_table_full(struct topa *topa)
{
        /* single-entry ToPA is a special case */
        if (!pt_cap_get(PT_CAP_topa_multiple_entries))
                return !!topa->last;

        return topa->last == TENTS_PER_PAGE - 1;
}

/**
 * topa_insert_pages() - create a list of ToPA tables
 * @buf:        PT buffer being initialized.
 * @gfp:        Allocation flags.
 *
 * This initializes a list of ToPA tables with entries from
 * the data_pages provided by rb_alloc_aux().
 *
 * Return:      0 on success or error code.
 */
static int topa_insert_pages(struct pt_buffer *buf, gfp_t gfp)
{
        struct topa *topa = buf->last;
        int order = 0;
        struct page *p;

        p = virt_to_page(buf->data_pages[buf->nr_pages]);
        if (PagePrivate(p))
                order = page_private(p);

        if (topa_table_full(topa)) {
                topa = topa_alloc(buf->cpu, gfp);
                if (!topa)
                        return -ENOMEM;

                topa_insert_table(buf, topa);
        }

        TOPA_ENTRY(topa, -1)->base = page_to_phys(p) >> TOPA_SHIFT;
        TOPA_ENTRY(topa, -1)->size = order;
        if (!buf->snapshot && !pt_cap_get(PT_CAP_topa_multiple_entries)) {
                TOPA_ENTRY(topa, -1)->intr = 1;
                TOPA_ENTRY(topa, -1)->stop = 1;
        }

        topa->last++;
        topa->size += sizes(order);

        buf->nr_pages += 1ul << order;

        return 0;
}

/**
 * pt_topa_dump() - print ToPA tables and their entries
 * @buf:        PT buffer.
 */
static void pt_topa_dump(struct pt_buffer *buf)
{
        struct topa *topa;

        list_for_each_entry(topa, &buf->tables, list) {
                int i;

                pr_debug("# table @%p (%016Lx), off %llx size %zx\n", topa->table,
                         topa->phys, topa->offset, topa->size);
                for (i = 0; i < TENTS_PER_PAGE; i++) {
                        pr_debug("# entry @%p (%lx sz %u %c%c%c) raw=%16llx\n",
                                 &topa->table[i],
                                 (unsigned long)topa->table[i].base << TOPA_SHIFT,
                                 sizes(topa->table[i].size),
                                 topa->table[i].end ?  'E' : ' ',
                                 topa->table[i].intr ? 'I' : ' ',
                                 topa->table[i].stop ? 'S' : ' ',
                                 *(u64 *)&topa->table[i]);
                        if ((pt_cap_get(PT_CAP_topa_multiple_entries) &&
                             topa->table[i].stop) ||
                            topa->table[i].end)
                                break;
                }
        }
}

/**
 * pt_buffer_advance() - advance to the next output region
 * @buf:        PT buffer.
 *
 * Advance the current pointers in the buffer to the next ToPA entry.
 */
static void pt_buffer_advance(struct pt_buffer *buf)
{
        buf->output_off = 0;
        buf->cur_idx++;

        if (buf->cur_idx == buf->cur->last) {
                if (buf->cur == buf->last)
                        buf->cur = buf->first;
                else
                        buf->cur = list_entry(buf->cur->list.next, struct topa,
                                              list);
                buf->cur_idx = 0;
        }
}

/**
 * pt_update_head() - calculate current offsets and sizes
 * @pt:         Per-cpu pt context.
 *
 * Update buffer's current write pointer position and data size.
 */
static void pt_update_head(struct pt *pt)
{
        struct pt_buffer *buf = perf_get_aux(&pt->handle);
        u64 topa_idx, base, old;

        /* offset of the first region in this table from the beginning of buf */
        base = buf->cur->offset + buf->output_off;

        /* offset of the current output region within this table */
        for (topa_idx = 0; topa_idx < buf->cur_idx; topa_idx++)
                base += sizes(buf->cur->table[topa_idx].size);

        if (buf->snapshot) {
                local_set(&buf->data_size, base);
        } else {
                old = (local64_xchg(&buf->head, base) &
                       ((buf->nr_pages << PAGE_SHIFT) - 1));
                if (base < old)
                        base += buf->nr_pages << PAGE_SHIFT;

                local_add(base - old, &buf->data_size);
        }
}

/**
 * pt_buffer_region() - obtain current output region's address
 * @buf:        PT buffer.
 */
static void *pt_buffer_region(struct pt_buffer *buf)
{
        return phys_to_virt(buf->cur->table[buf->cur_idx].base << TOPA_SHIFT);
}

/**
 * pt_buffer_region_size() - obtain current output region's size
 * @buf:        PT buffer.
 */
static size_t pt_buffer_region_size(struct pt_buffer *buf)
{
        return sizes(buf->cur->table[buf->cur_idx].size);
}

/**
 * pt_handle_status() - take care of possible status conditions
 * @pt:         Per-cpu pt context.
 */
static void pt_handle_status(struct pt *pt)
{
        struct pt_buffer *buf = perf_get_aux(&pt->handle);
        int advance = 0;
        u64 status;

        rdmsrl(MSR_IA32_RTIT_STATUS, status);

        if (status & RTIT_STATUS_ERROR) {
                pr_err_ratelimited("ToPA ERROR encountered, trying to recover\n");
                pt_topa_dump(buf);
                status &= ~RTIT_STATUS_ERROR;
        }

        if (status & RTIT_STATUS_STOPPED) {
                status &= ~RTIT_STATUS_STOPPED;

                /*
                 * On systems that only do single-entry ToPA, hitting STOP
                 * means we are already losing data; need to let the decoder
                 * know.
                 */
                if (!pt_cap_get(PT_CAP_topa_multiple_entries) ||
                    buf->output_off == sizes(TOPA_ENTRY(buf->cur, buf->cur_idx)->size)) {
                        local_inc(&buf->lost);
                        advance++;
                }
        }

        /*
         * Also on single-entry ToPA implementations, interrupt will come
         * before the output reaches its output region's boundary.
         */
        if (!pt_cap_get(PT_CAP_topa_multiple_entries) && !buf->snapshot &&
            pt_buffer_region_size(buf) - buf->output_off <= TOPA_PMI_MARGIN) {
                void *head = pt_buffer_region(buf);

                /* everything within this margin needs to be zeroed out */
                memset(head + buf->output_off, 0,
                       pt_buffer_region_size(buf) -
                       buf->output_off);
                advance++;
        }

        if (advance)
                pt_buffer_advance(buf);

        wrmsrl(MSR_IA32_RTIT_STATUS, status);
}

/**
 * pt_read_offset() - translate registers into buffer pointers
 * @buf:        PT buffer.
 *
 * Set buffer's output pointers from MSR values.
 */
static void pt_read_offset(struct pt_buffer *buf)
{
        u64 offset, base_topa;

        rdmsrl(MSR_IA32_RTIT_OUTPUT_BASE, base_topa);
        buf->cur = phys_to_virt(base_topa);

        rdmsrl(MSR_IA32_RTIT_OUTPUT_MASK, offset);
        /* offset within current output region */
        buf->output_off = offset >> 32;
        /* index of current output region within this table */
        buf->cur_idx = (offset & 0xffffff80) >> 7;
}

/**
 * pt_topa_next_entry() - obtain index of the first page in the next ToPA entry
 * @buf:        PT buffer.
 * @pg:         Page offset in the buffer.
 *
 * When advancing to the next output region (ToPA entry), given a page offset
 * into the buffer, we need to find the offset of the first page in the next
 * region.
 */
static unsigned int pt_topa_next_entry(struct pt_buffer *buf, unsigned int pg)
{
        struct topa_entry *te = buf->topa_index[pg];

        /* one region */
        if (buf->first == buf->last && buf->first->last == 1)
                return pg;

        do {
                pg++;
                pg &= buf->nr_pages - 1;
        } while (buf->topa_index[pg] == te);

        return pg;
}

/**
 * pt_buffer_reset_markers() - place interrupt and stop bits in the buffer
 * @buf:        PT buffer.
 * @handle:     Current output handle.
 *
 * Place INT and STOP marks to prevent overwriting old data that the consumer
 * hasn't yet collected and waking up the consumer after a certain fraction of
 * the buffer has filled up. Only needed and sensible for non-snapshot counters.
 *
 * This obviously relies on buf::head to figure out buffer markers, so it has
 * to be called after pt_buffer_reset_offsets() and before the hardware tracing
 * is enabled.
 */
static int pt_buffer_reset_markers(struct pt_buffer *buf,
                                   struct perf_output_handle *handle)

{
        unsigned long head = local64_read(&buf->head);
        unsigned long idx, npages, wakeup;

        /* can't stop in the middle of an output region */
        if (buf->output_off + handle->size + 1 <
            sizes(TOPA_ENTRY(buf->cur, buf->cur_idx)->size))
                return -EINVAL;


        /* single entry ToPA is handled by marking all regions STOP=1 INT=1 */
        if (!pt_cap_get(PT_CAP_topa_multiple_entries))
                return 0;

        /* clear STOP and INT from current entry */
        buf->topa_index[buf->stop_pos]->stop = 0;
        buf->topa_index[buf->intr_pos]->intr = 0;

        /* how many pages till the STOP marker */
        npages = handle->size >> PAGE_SHIFT;

        /* if it's on a page boundary, fill up one more page */
        if (!offset_in_page(head + handle->size + 1))
                npages++;

        idx = (head >> PAGE_SHIFT) + npages;
        idx &= buf->nr_pages - 1;
        buf->stop_pos = idx;

        wakeup = handle->wakeup >> PAGE_SHIFT;

        /* in the worst case, wake up the consumer one page before hard stop */
        idx = (head >> PAGE_SHIFT) + npages - 1;
        if (idx > wakeup)
                idx = wakeup;

        idx &= buf->nr_pages - 1;
        buf->intr_pos = idx;

        buf->topa_index[buf->stop_pos]->stop = 1;
        buf->topa_index[buf->intr_pos]->intr = 1;

        return 0;
}

/**
 * pt_buffer_setup_topa_index() - build topa_index[] table of regions
 * @buf:        PT buffer.
 *
 * topa_index[] references output regions indexed by offset into the
 * buffer for purposes of quick reverse lookup.
 */
static void pt_buffer_setup_topa_index(struct pt_buffer *buf)
{
        struct topa *cur = buf->first, *prev = buf->last;
        struct topa_entry *te_cur = TOPA_ENTRY(cur, 0),
                *te_prev = TOPA_ENTRY(prev, prev->last - 1);
        int pg = 0, idx = 0;

        while (pg < buf->nr_pages) {
                int tidx;

                /* pages within one topa entry */
                for (tidx = 0; tidx < 1 << te_cur->size; tidx++, pg++)
                        buf->topa_index[pg] = te_prev;

                te_prev = te_cur;

                if (idx == cur->last - 1) {
                        /* advance to next topa table */
                        idx = 0;
                        cur = list_entry(cur->list.next, struct topa, list);
                } else {
                        idx++;
                }
                te_cur = TOPA_ENTRY(cur, idx);
        }

}

/**
 * pt_buffer_reset_offsets() - adjust buffer's write pointers from aux_head
 * @buf:        PT buffer.
 * @head:       Write pointer (aux_head) from AUX buffer.
 *
 * Find the ToPA table and entry corresponding to given @head and set buffer's
 * "current" pointers accordingly. This is done after we have obtained the
 * current aux_head position from a successful call to perf_aux_output_begin()
 * to make sure the hardware is writing to the right place.
 *
 * This function modifies buf::{cur,cur_idx,output_off} that will be programmed
 * into PT msrs when the tracing is enabled and buf::head and buf::data_size,
 * which are used to determine INT and STOP markers' locations by a subsequent
 * call to pt_buffer_reset_markers().
 */
static void pt_buffer_reset_offsets(struct pt_buffer *buf, unsigned long head)
{
        int pg;

        if (buf->snapshot)
                head &= (buf->nr_pages << PAGE_SHIFT) - 1;

        pg = (head >> PAGE_SHIFT) & (buf->nr_pages - 1);
        pg = pt_topa_next_entry(buf, pg);

        buf->cur = (struct topa *)((unsigned long)buf->topa_index[pg] & PAGE_MASK);
        buf->cur_idx = ((unsigned long)buf->topa_index[pg] -
                        (unsigned long)buf->cur) / sizeof(struct topa_entry);
        buf->output_off = head & (sizes(buf->cur->table[buf->cur_idx].size) - 1);

        local64_set(&buf->head, head);
        local_set(&buf->data_size, 0);
}

/**
 * pt_buffer_fini_topa() - deallocate ToPA structure of a buffer
 * @buf:        PT buffer.
 */
static void pt_buffer_fini_topa(struct pt_buffer *buf)
{
        struct topa *topa, *iter;

        list_for_each_entry_safe(topa, iter, &buf->tables, list) {
                /*
                 * right now, this is in free_aux() path only, so
                 * no need to unlink this table from the list
                 */
                topa_free(topa);
        }
}

/**
 * pt_buffer_init_topa() - initialize ToPA table for pt buffer
 * @buf:        PT buffer.
 * @size:       Total size of all regions within this ToPA.
 * @gfp:        Allocation flags.
 */
static int pt_buffer_init_topa(struct pt_buffer *buf, unsigned long nr_pages,
                               gfp_t gfp)
{
        struct topa *topa;
        int err;

        topa = topa_alloc(buf->cpu, gfp);
        if (!topa)
                return -ENOMEM;

        topa_insert_table(buf, topa);

        while (buf->nr_pages < nr_pages) {
                err = topa_insert_pages(buf, gfp);
                if (err) {
                        pt_buffer_fini_topa(buf);
                        return -ENOMEM;
                }
        }

        pt_buffer_setup_topa_index(buf);

        /* link last table to the first one, unless we're double buffering */
        if (pt_cap_get(PT_CAP_topa_multiple_entries)) {
                TOPA_ENTRY(buf->last, -1)->base = buf->first->phys >> TOPA_SHIFT;
                TOPA_ENTRY(buf->last, -1)->end = 1;
        }

        pt_topa_dump(buf);
        return 0;
}

/**
 * pt_buffer_setup_aux() - set up topa tables for a PT buffer
 * @cpu:        Cpu on which to allocate, -1 means current.
 * @pages:      Array of pointers to buffer pages passed from perf core.
 * @nr_pages:   Number of pages in the buffer.
 * @snapshot:   If this is a snapshot/overwrite counter.
 *
 * This is a pmu::setup_aux callback that sets up ToPA tables and all the
 * bookkeeping for an AUX buffer.
 *
 * Return:      Our private PT buffer structure.
 */
static void *
pt_buffer_setup_aux(int cpu, void **pages, int nr_pages, bool snapshot)
{
        struct pt_buffer *buf;
        int node, ret;

        if (!nr_pages)
                return NULL;

        if (cpu == -1)
                cpu = raw_smp_processor_id();
        node = cpu_to_node(cpu);

        buf = kzalloc_node(offsetof(struct pt_buffer, topa_index[nr_pages]),
                           GFP_KERNEL, node);
        if (!buf)
                return NULL;

        buf->cpu = cpu;
        buf->snapshot = snapshot;
        buf->data_pages = pages;

        INIT_LIST_HEAD(&buf->tables);

        ret = pt_buffer_init_topa(buf, nr_pages, GFP_KERNEL);
        if (ret) {
                kfree(buf);
                return NULL;
        }

        return buf;
}

/**
 * pt_buffer_free_aux() - perf AUX deallocation path callback
 * @data:       PT buffer.
 */
static void pt_buffer_free_aux(void *data)
{
        struct pt_buffer *buf = data;

        pt_buffer_fini_topa(buf);
        kfree(buf);
}

/**
 * pt_buffer_is_full() - check if the buffer is full
 * @buf:        PT buffer.
 * @pt:         Per-cpu pt handle.
 *
 * If the user hasn't read data from the output region that aux_head
 * points to, the buffer is considered full: the user needs to read at
 * least this region and update aux_tail to point past it.
 */
static bool pt_buffer_is_full(struct pt_buffer *buf, struct pt *pt)
{
        if (buf->snapshot)
                return false;

        if (local_read(&buf->data_size) >= pt->handle.size)
                return true;

        return false;
}

/**
 * intel_pt_interrupt() - PT PMI handler
 */
void intel_pt_interrupt(void)
{
        struct pt *pt = this_cpu_ptr(&pt_ctx);
        struct pt_buffer *buf;
        struct perf_event *event = pt->handle.event;

        /*
         * There may be a dangling PT bit in the interrupt status register
         * after PT has been disabled by pt_event_stop(). Make sure we don't
         * do anything (particularly, re-enable) for this event here.
         */
        if (!ACCESS_ONCE(pt->handle_nmi))
                return;

        pt_config_start(false);

        if (!event)
                return;

        buf = perf_get_aux(&pt->handle);
        if (!buf)
                return;

        pt_read_offset(buf);

        pt_handle_status(pt);

        pt_update_head(pt);

        perf_aux_output_end(&pt->handle, local_xchg(&buf->data_size, 0),
                            local_xchg(&buf->lost, 0));

        if (!event->hw.state) {
                int ret;

                buf = perf_aux_output_begin(&pt->handle, event);
                if (!buf) {
                        event->hw.state = PERF_HES_STOPPED;
                        return;
                }

                pt_buffer_reset_offsets(buf, pt->handle.head);
                /* snapshot counters don't use PMI, so it's safe */
                ret = pt_buffer_reset_markers(buf, &pt->handle);
                if (ret) {
                        perf_aux_output_end(&pt->handle, 0, true);
                        return;
                }

                pt_config_buffer(buf->cur->table, buf->cur_idx,
                                 buf->output_off);
                pt_config(event);
        }
}

/*
 * PMU callbacks
 */

static void pt_event_start(struct perf_event *event, int mode)
{
        struct pt *pt = this_cpu_ptr(&pt_ctx);
        struct pt_buffer *buf = perf_get_aux(&pt->handle);

        if (!buf || pt_buffer_is_full(buf, pt)) {
                event->hw.state = PERF_HES_STOPPED;
                return;
        }

        ACCESS_ONCE(pt->handle_nmi) = 1;
        event->hw.state = 0;

        pt_config_buffer(buf->cur->table, buf->cur_idx,
                         buf->output_off);
        pt_config(event);
}

static void pt_event_stop(struct perf_event *event, int mode)
{
        struct pt *pt = this_cpu_ptr(&pt_ctx);

        /*
         * Protect against the PMI racing with disabling wrmsr,
         * see comment in intel_pt_interrupt().
         */
        ACCESS_ONCE(pt->handle_nmi) = 0;
        pt_config_start(false);

        if (event->hw.state == PERF_HES_STOPPED)
                return;

        event->hw.state = PERF_HES_STOPPED;

        if (mode & PERF_EF_UPDATE) {
                struct pt_buffer *buf = perf_get_aux(&pt->handle);

                if (!buf)
                        return;

                if (WARN_ON_ONCE(pt->handle.event != event))
                        return;

                pt_read_offset(buf);

                pt_handle_status(pt);

                pt_update_head(pt);
        }
}

static void pt_event_del(struct perf_event *event, int mode)
{
        struct pt *pt = this_cpu_ptr(&pt_ctx);
        struct pt_buffer *buf;

        pt_event_stop(event, PERF_EF_UPDATE);

        buf = perf_get_aux(&pt->handle);

        if (buf) {
                if (buf->snapshot)
                        pt->handle.head =
                                local_xchg(&buf->data_size,
                                           buf->nr_pages << PAGE_SHIFT);
                perf_aux_output_end(&pt->handle, local_xchg(&buf->data_size, 0),
                                    local_xchg(&buf->lost, 0));
        }
}

static int pt_event_add(struct perf_event *event, int mode)
{
        struct pt_buffer *buf;
        struct pt *pt = this_cpu_ptr(&pt_ctx);
        struct hw_perf_event *hwc = &event->hw;
        int ret = -EBUSY;

        if (pt->handle.event)
                goto fail;

        buf = perf_aux_output_begin(&pt->handle, event);
        ret = -EINVAL;
        if (!buf)
                goto fail_stop;

        pt_buffer_reset_offsets(buf, pt->handle.head);
        if (!buf->snapshot) {
                ret = pt_buffer_reset_markers(buf, &pt->handle);
                if (ret)
                        goto fail_end_stop;
        }

        if (mode & PERF_EF_START) {
                pt_event_start(event, 0);
                ret = -EBUSY;
                if (hwc->state == PERF_HES_STOPPED)
                        goto fail_end_stop;
        } else {
                hwc->state = PERF_HES_STOPPED;
        }

        return 0;

fail_end_stop:
        perf_aux_output_end(&pt->handle, 0, true);
fail_stop:
        hwc->state = PERF_HES_STOPPED;
fail:
        return ret;
}

static void pt_event_read(struct perf_event *event)
{
}

static void pt_event_destroy(struct perf_event *event)
{
        x86_del_exclusive(x86_lbr_exclusive_pt);
}

static int pt_event_init(struct perf_event *event)
{
        if (event->attr.type != pt_pmu.pmu.type)
                return -ENOENT;

        if (!pt_event_valid(event))
                return -EINVAL;

        if (x86_add_exclusive(x86_lbr_exclusive_pt))
                return -EBUSY;

        event->destroy = pt_event_destroy;

        return 0;
}

static __init int pt_init(void)
{
        int ret, cpu, prior_warn = 0;

        BUILD_BUG_ON(sizeof(struct topa) > PAGE_SIZE);

        if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_INTEL_PT))
                return -ENODEV;

        get_online_cpus();
        for_each_online_cpu(cpu) {
                u64 ctl;

                ret = rdmsrl_safe_on_cpu(cpu, MSR_IA32_RTIT_CTL, &ctl);
                if (!ret && (ctl & RTIT_CTL_TRACEEN))
                        prior_warn++;
        }
        put_online_cpus();

        if (prior_warn) {
                x86_add_exclusive(x86_lbr_exclusive_pt);
                pr_warn("PT is enabled at boot time, doing nothing\n");

                return -EBUSY;
        }

        ret = pt_pmu_hw_init();
        if (ret)
                return ret;

        if (!pt_cap_get(PT_CAP_topa_output)) {
                pr_warn("ToPA output is not supported on this CPU\n");
                return -ENODEV;
        }

        if (!pt_cap_get(PT_CAP_topa_multiple_entries))
                pt_pmu.pmu.capabilities =
                        PERF_PMU_CAP_AUX_NO_SG | PERF_PMU_CAP_AUX_SW_DOUBLEBUF;

        pt_pmu.pmu.capabilities |= PERF_PMU_CAP_EXCLUSIVE | PERF_PMU_CAP_ITRACE;
        pt_pmu.pmu.attr_groups  = pt_attr_groups;
        pt_pmu.pmu.task_ctx_nr  = perf_sw_context;
        pt_pmu.pmu.event_init   = pt_event_init;
        pt_pmu.pmu.add          = pt_event_add;
        pt_pmu.pmu.del          = pt_event_del;
        pt_pmu.pmu.start        = pt_event_start;
        pt_pmu.pmu.stop         = pt_event_stop;
        pt_pmu.pmu.read         = pt_event_read;
        pt_pmu.pmu.setup_aux    = pt_buffer_setup_aux;
        pt_pmu.pmu.free_aux     = pt_buffer_free_aux;
        ret = perf_pmu_register(&pt_pmu.pmu, "intel_pt", -1);

        return ret;
}
arch_initcall(pt_init);