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x86_64, entry: Use split-phase syscall_trace_enter for 64-bit syscalls

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On KVM on my box, this reduces the overhead from an always-accept
seccomp filter from ~130ns to ~17ns.  Most of that comes from
avoiding IRET on every syscall when seccomp is enabled.

In extremely approximate hacked-up benchmarking, just bypassing IRET
saves about 80ns, so there's another 43ns of savings here from
simplifying the seccomp path.

The diffstat is also rather nice :)

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/a3dbd267ee990110478d349f78cccfdac5497a84.1409954077.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Andy Lutomirski 2014-09-05 15:13:56 -07:00 committed by H. Peter Anvin
parent 54eea9957f
commit 1dcf74f6ed
1 changed files with 15 additions and 23 deletions
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38
arch/x86/kernel/entry_64.S
View file

@ -477,22 +477,6 @@ sysret_signal:
jmp int_check_syscall_exit_work
#ifdef CONFIG_AUDITSYSCALL
/*
* Fast path for syscall audit without full syscall trace.
* We just call __audit_syscall_entry() directly, and then
* jump back to the normal fast path.
*/
auditsys:
movq %r10,%r9 /* 6th arg: 4th syscall arg */
movq %rdx,%r8 /* 5th arg: 3rd syscall arg */
movq %rsi,%rcx /* 4th arg: 2nd syscall arg */
movq %rdi,%rdx /* 3rd arg: 1st syscall arg */
movq %rax,%rsi /* 2nd arg: syscall number */
movl $AUDIT_ARCH_X86_64,%edi /* 1st arg: audit arch */
call __audit_syscall_entry
LOAD_ARGS 0 /* reload call-clobbered registers */
jmp system_call_fastpath
/*
* Return fast path for syscall audit. Call __audit_syscall_exit()
* directly and then jump back to the fast path with TIF_SYSCALL_AUDIT
@ -510,17 +494,25 @@ sysret_audit:
/* Do syscall tracing */
tracesys:
#ifdef CONFIG_AUDITSYSCALL
testl $(_TIF_WORK_SYSCALL_ENTRY & ~_TIF_SYSCALL_AUDIT),TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)
jz auditsys
#endif
leaq -REST_SKIP(%rsp), %rdi
movq $AUDIT_ARCH_X86_64, %rsi
call syscall_trace_enter_phase1
test %rax, %rax
jnz tracesys_phase2 /* if needed, run the slow path */
LOAD_ARGS 0 /* else restore clobbered regs */
jmp system_call_fastpath /* and return to the fast path */
tracesys_phase2:
SAVE_REST
FIXUP_TOP_OF_STACK %rdi
movq %rsp,%rdi
call syscall_trace_enter
movq %rsp, %rdi
movq $AUDIT_ARCH_X86_64, %rsi
movq %rax,%rdx
call syscall_trace_enter_phase2
/*
* Reload arg registers from stack in case ptrace changed them.
* We don't reload %rax because syscall_trace_enter() returned
* We don't reload %rax because syscall_trace_entry_phase2() returned
* the value it wants us to use in the table lookup.
*/
LOAD_ARGS ARGOFFSET, 1