Commit 29722cd4 authored by Denys Vlasenko's avatar Denys Vlasenko Committed by Ingo Molnar

x86/asm/entry/64: Save R11 into pt_regs->flags on SYSCALL64 fastpath

Before this patch, R11 was saved in pt_regs->r11.

Which looks natural, but requires messy shuffling to/from iret
frame whenever ptrace or e.g. sys_iopl() wants to modify flags -
because that's how this register is used by SYSCALL/SYSRET.

This patch saves R11 in pt_regs->flags, and uses that value for
the SYSRET64 instruction. Shuffling is eliminated.

FIXUP/RESTORE_TOP_OF_STACK are simplified.

stub_iopl is no longer needed: pt_regs->flags needs no fixing up.

Testing shows that syscall fast path is ~54.3 ns before
and after the patch (on 2.7 GHz Sandy Bridge CPU).
Signed-off-by: default avatarDenys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
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: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1425926364-9526-2-git-send-email-dvlasenk@redhat.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 3e1aa7cb
...@@ -95,9 +95,11 @@ For 32-bit we have the following conventions - kernel is built with ...@@ -95,9 +95,11 @@ For 32-bit we have the following conventions - kernel is built with
CFI_ADJUST_CFA_OFFSET 15*8+\addskip CFI_ADJUST_CFA_OFFSET 15*8+\addskip
.endm .endm
.macro SAVE_C_REGS_HELPER offset=0 rax=1 rcx=1 r8plus=1 .macro SAVE_C_REGS_HELPER offset=0 rax=1 rcx=1 r8910=1 r11=1
.if \r8plus .if \r11
movq_cfi r11, 6*8+\offset movq_cfi r11, 6*8+\offset
.endif
.if \r8910
movq_cfi r10, 7*8+\offset movq_cfi r10, 7*8+\offset
movq_cfi r9, 8*8+\offset movq_cfi r9, 8*8+\offset
movq_cfi r8, 9*8+\offset movq_cfi r8, 9*8+\offset
...@@ -113,16 +115,19 @@ For 32-bit we have the following conventions - kernel is built with ...@@ -113,16 +115,19 @@ For 32-bit we have the following conventions - kernel is built with
movq_cfi rdi, 14*8+\offset movq_cfi rdi, 14*8+\offset
.endm .endm
.macro SAVE_C_REGS offset=0 .macro SAVE_C_REGS offset=0
SAVE_C_REGS_HELPER \offset, 1, 1, 1 SAVE_C_REGS_HELPER \offset, 1, 1, 1, 1
.endm .endm
.macro SAVE_C_REGS_EXCEPT_RAX_RCX offset=0 .macro SAVE_C_REGS_EXCEPT_RAX_RCX offset=0
SAVE_C_REGS_HELPER \offset, 0, 0, 1 SAVE_C_REGS_HELPER \offset, 0, 0, 1, 1
.endm .endm
.macro SAVE_C_REGS_EXCEPT_R891011 .macro SAVE_C_REGS_EXCEPT_R891011
SAVE_C_REGS_HELPER 0, 1, 1, 0 SAVE_C_REGS_HELPER 0, 1, 1, 0, 0
.endm .endm
.macro SAVE_C_REGS_EXCEPT_RCX_R891011 .macro SAVE_C_REGS_EXCEPT_RCX_R891011
SAVE_C_REGS_HELPER 0, 1, 0, 0 SAVE_C_REGS_HELPER 0, 1, 0, 0, 0
.endm
.macro SAVE_C_REGS_EXCEPT_RAX_RCX_R11
SAVE_C_REGS_HELPER 0, 0, 0, 1, 0
.endm .endm
.macro SAVE_EXTRA_REGS offset=0 .macro SAVE_EXTRA_REGS offset=0
...@@ -179,6 +184,9 @@ For 32-bit we have the following conventions - kernel is built with ...@@ -179,6 +184,9 @@ For 32-bit we have the following conventions - kernel is built with
.macro RESTORE_C_REGS_EXCEPT_R11 .macro RESTORE_C_REGS_EXCEPT_R11
RESTORE_C_REGS_HELPER 1,1,0,1,1 RESTORE_C_REGS_HELPER 1,1,0,1,1
.endm .endm
.macro RESTORE_C_REGS_EXCEPT_RCX_R11
RESTORE_C_REGS_HELPER 1,0,0,1,1
.endm
.macro RESTORE_RSI_RDI .macro RESTORE_RSI_RDI
RESTORE_C_REGS_HELPER 0,0,0,0,0 RESTORE_C_REGS_HELPER 0,0,0,0,0
.endm .endm
......
...@@ -121,14 +121,12 @@ ENDPROC(native_usergs_sysret64) ...@@ -121,14 +121,12 @@ ENDPROC(native_usergs_sysret64)
#endif #endif
/* /*
* C code is not supposed to know about undefined top of stack. Every time * C code is not supposed to know that the iret frame is not populated.
* a C function with an pt_regs argument is called from the SYSCALL based * Every time a C function with an pt_regs argument is called from
* fast path FIXUP_TOP_OF_STACK is needed. * the SYSCALL based fast path FIXUP_TOP_OF_STACK is needed.
* RESTORE_TOP_OF_STACK syncs the syscall state after any possible ptregs * RESTORE_TOP_OF_STACK syncs the syscall state after any possible ptregs
* manipulation. * manipulation.
*/ */
/* %rsp:at FRAMEEND */
.macro FIXUP_TOP_OF_STACK tmp offset=0 .macro FIXUP_TOP_OF_STACK tmp offset=0
movq PER_CPU_VAR(old_rsp),\tmp movq PER_CPU_VAR(old_rsp),\tmp
movq \tmp,RSP+\offset(%rsp) movq \tmp,RSP+\offset(%rsp)
...@@ -136,15 +134,13 @@ ENDPROC(native_usergs_sysret64) ...@@ -136,15 +134,13 @@ ENDPROC(native_usergs_sysret64)
movq $__USER_CS,CS+\offset(%rsp) movq $__USER_CS,CS+\offset(%rsp)
movq RIP+\offset(%rsp),\tmp /* get rip */ movq RIP+\offset(%rsp),\tmp /* get rip */
movq \tmp,RCX+\offset(%rsp) /* copy it to rcx as sysret would do */ movq \tmp,RCX+\offset(%rsp) /* copy it to rcx as sysret would do */
movq R11+\offset(%rsp),\tmp /* get eflags */ movq EFLAGS+\offset(%rsp),\tmp /* ditto for rflags->r11 */
movq \tmp,EFLAGS+\offset(%rsp) movq \tmp,R11+\offset(%rsp)
.endm .endm
.macro RESTORE_TOP_OF_STACK tmp offset=0 .macro RESTORE_TOP_OF_STACK tmp offset=0
movq RSP+\offset(%rsp),\tmp movq RSP+\offset(%rsp),\tmp
movq \tmp,PER_CPU_VAR(old_rsp) movq \tmp,PER_CPU_VAR(old_rsp)
movq EFLAGS+\offset(%rsp),\tmp
movq \tmp,R11+\offset(%rsp)
.endm .endm
/* /*
...@@ -257,9 +253,10 @@ GLOBAL(system_call_after_swapgs) ...@@ -257,9 +253,10 @@ GLOBAL(system_call_after_swapgs)
*/ */
ENABLE_INTERRUPTS(CLBR_NONE) ENABLE_INTERRUPTS(CLBR_NONE)
ALLOC_PT_GPREGS_ON_STACK 8 /* +8: space for orig_ax */ ALLOC_PT_GPREGS_ON_STACK 8 /* +8: space for orig_ax */
SAVE_C_REGS_EXCEPT_RAX_RCX SAVE_C_REGS_EXCEPT_RAX_RCX_R11
movq $-ENOSYS,RAX(%rsp) movq $-ENOSYS,RAX(%rsp)
movq_cfi rax,ORIG_RAX movq_cfi rax,ORIG_RAX
movq %r11,EFLAGS(%rsp)
movq %rcx,RIP(%rsp) movq %rcx,RIP(%rsp)
CFI_REL_OFFSET rip,RIP CFI_REL_OFFSET rip,RIP
testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags+THREAD_INFO(%rsp,RIP) testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags+THREAD_INFO(%rsp,RIP)
...@@ -277,7 +274,7 @@ system_call_fastpath: ...@@ -277,7 +274,7 @@ system_call_fastpath:
movq %rax,RAX(%rsp) movq %rax,RAX(%rsp)
/* /*
* Syscall return path ending with SYSRET (fast path) * Syscall return path ending with SYSRET (fast path)
* Has incomplete stack frame and undefined top of stack. * Has incompletely filled pt_regs, iret frame is also incomplete.
*/ */
ret_from_sys_call: ret_from_sys_call:
testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP) testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP)
...@@ -291,9 +288,10 @@ ret_from_sys_call: ...@@ -291,9 +288,10 @@ ret_from_sys_call:
* sysretq will re-enable interrupts: * sysretq will re-enable interrupts:
*/ */
TRACE_IRQS_ON TRACE_IRQS_ON
RESTORE_C_REGS_EXCEPT_RCX RESTORE_C_REGS_EXCEPT_RCX_R11
movq RIP(%rsp),%rcx movq RIP(%rsp),%rcx
CFI_REGISTER rip,rcx CFI_REGISTER rip,rcx
movq EFLAGS(%rsp),%r11
/*CFI_REGISTER rflags,r11*/ /*CFI_REGISTER rflags,r11*/
movq PER_CPU_VAR(old_rsp), %rsp movq PER_CPU_VAR(old_rsp), %rsp
/* /*
......
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