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| author | Peter Zijlstra <peterz@infradead.org> | 2021-03-12 14:32:54 +0300 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2021-03-15 18:24:59 +0300 |
| commit | a89dfde3dc3c2dbf56910af75e2d8b11ec5308f6 (patch) | |
| tree | 1f5d63a4ea45af7d513ce044362993174ad52694 /arch/x86/include/asm/jump_label.h | |
| parent | 59eca2fa1934de42d8aa44d3bef655c92ea69703 (diff) | |
| download | linux-a89dfde3dc3c2dbf56910af75e2d8b11ec5308f6.tar.xz | |
x86: Remove dynamic NOP selection
This ensures that a NOP is a NOP and not a random other instruction that
is also a NOP. It allows simplification of dynamic code patching that
wants to verify existing code before writing new instructions (ftrace,
jump_label, static_call, etc..).
Differentiating on NOPs is not a feature.
This pessimises 32bit (DONTCARE) and 32bit on 64bit CPUs (CARELESS).
32bit is not a performance target.
Everything x86_64 since AMD K10 (2007) and Intel IvyBridge (2012) is
fine with using NOPL (as opposed to prefix NOP). And per FEATURE_NOPL
being required for x86_64, all x86_64 CPUs can use NOPL. So stop
caring about NOPs, simplify things and get on with life.
[ The problem seems to be that some uarchs can only decode NOPL on a
single front-end port while others have severe decode penalties for
excessive prefixes. All modern uarchs can handle both, except Atom,
which has prefix penalties. ]
[ Also, much doubt you can actually measure any of this on normal
workloads. ]
After this, FEATURE_NOPL is unused except for required-features for
x86_64. FEATURE_K8 is only used for PTI.
[ bp: Kernel build measurements showed ~0.3s slowdown on Sandybridge
which is hardly a slowdown. Get rid of X86_FEATURE_K7, while at it. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Alexei Starovoitov <alexei.starovoitov@gmail.com> # bpf
Acked-by: Linus Torvalds <torvalds@linuxfoundation.org>
Link: https://lkml.kernel.org/r/20210312115749.065275711@infradead.org
Diffstat (limited to 'arch/x86/include/asm/jump_label.h')
| -rw-r--r-- | arch/x86/include/asm/jump_label.h | 12 |
1 files changed, 3 insertions, 9 deletions
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h index 06c3cc22a058..5ce342b91ff3 100644 --- a/arch/x86/include/asm/jump_label.h +++ b/arch/x86/include/asm/jump_label.h @@ -6,12 +6,6 @@ #define JUMP_LABEL_NOP_SIZE 5 -#ifdef CONFIG_X86_64 -# define STATIC_KEY_INIT_NOP P6_NOP5_ATOMIC -#else -# define STATIC_KEY_INIT_NOP GENERIC_NOP5_ATOMIC -#endif - #include <asm/asm.h> #include <asm/nops.h> @@ -23,7 +17,7 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool branch) { asm_volatile_goto("1:" - ".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t" + ".byte " __stringify(BYTES_NOP5) "\n\t" ".pushsection __jump_table, \"aw\" \n\t" _ASM_ALIGN "\n\t" ".long 1b - ., %l[l_yes] - . \n\t" @@ -63,7 +57,7 @@ l_yes: .long \target - .Lstatic_jump_after_\@ .Lstatic_jump_after_\@: .else - .byte STATIC_KEY_INIT_NOP + .byte BYTES_NOP5 .endif .pushsection __jump_table, "aw" _ASM_ALIGN @@ -75,7 +69,7 @@ l_yes: .macro STATIC_JUMP_IF_FALSE target, key, def .Lstatic_jump_\@: .if \def - .byte STATIC_KEY_INIT_NOP + .byte BYTES_NOP5 .else /* Equivalent to "jmp.d32 \target" */ .byte 0xe9 |