x86/asm/entry/64: Simplify optimistic SYSRET

Avoid redundant load of %r11 (it is already loaded a few
instructions before).

Also simplify %rsp restoration, instead of two steps:

         add $0x80, %rsp
         mov 0x18(%rsp), %rsp

we can do a simplified single step to restore user-space RSP:

         mov 0x98(%rsp), %rsp

and get the same result.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
[ Clarified the changelog. ]
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1aef69b346a6db0d99cdfb0f5ba83e8c985e27d7.1424989793.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h
index 337423590b08bc9ebab72db831f89eb7c85a6eb2..f1a962ff7ddfc5a5f30365edbfb02b0bdfb13ef8 100644 (file)
--- a/arch/x86/include/asm/calling.h
+++ b/arch/x86/include/asm/calling.h
@@ -176,6 +176,9 @@ For 32-bit we have the following conventions - kernel is built with
        .macro RESTORE_C_REGS_EXCEPT_RCX
        RESTORE_C_REGS_HELPER 1,0,1,1,1
        .endm
+       .macro RESTORE_C_REGS_EXCEPT_R11
+       RESTORE_C_REGS_HELPER 1,1,0,1,1
+       .endm
        .macro RESTORE_RSI_RDI
        RESTORE_C_REGS_HELPER 0,0,0,0,0
        .endm

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 858e94e86f5e293cb91030fb7f0bef39a4360c31..bc1527889c406a95a1f22845ee31856c74636cec 100644 (file)
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -757,9 +757,9 @@ retint_swapgs:              /* return to user-space */
         */
 irq_return_via_sysret:
        CFI_REMEMBER_STATE
-       RESTORE_C_REGS
-       REMOVE_PT_GPREGS_FROM_STACK 8
-       movq (RSP-RIP)(%rsp),%rsp
+       /* r11 is already restored (see code above) */
+       RESTORE_C_REGS_EXCEPT_R11
+       movq RSP(%rsp),%rsp
        USERGS_SYSRET64
        CFI_RESTORE_STATE