diff options
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/nops.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/nops.h')
-rw-r--r-- | arch/x86/include/asm/nops.h | 176 |
1 files changed, 55 insertions, 121 deletions
diff --git a/arch/x86/include/asm/nops.h b/arch/x86/include/asm/nops.h index 12f12b5cf2ca..c1e5e818ba16 100644 --- a/arch/x86/include/asm/nops.h +++ b/arch/x86/include/asm/nops.h @@ -4,89 +4,58 @@ /* * Define nops for use with alternative() and for tracing. - * - * *_NOP5_ATOMIC must be a single instruction. */ -#define NOP_DS_PREFIX 0x3e +#ifndef CONFIG_64BIT -/* generic versions from gas - 1: nop - the following instructions are NOT nops in 64-bit mode, - for 64-bit mode use K8 or P6 nops instead - 2: movl %esi,%esi - 3: leal 0x00(%esi),%esi - 4: leal 0x00(,%esi,1),%esi - 6: leal 0x00000000(%esi),%esi - 7: leal 0x00000000(,%esi,1),%esi -*/ -#define GENERIC_NOP1 0x90 -#define GENERIC_NOP2 0x89,0xf6 -#define GENERIC_NOP3 0x8d,0x76,0x00 -#define GENERIC_NOP4 0x8d,0x74,0x26,0x00 -#define GENERIC_NOP5 GENERIC_NOP1,GENERIC_NOP4 -#define GENERIC_NOP6 0x8d,0xb6,0x00,0x00,0x00,0x00 -#define GENERIC_NOP7 0x8d,0xb4,0x26,0x00,0x00,0x00,0x00 -#define GENERIC_NOP8 GENERIC_NOP1,GENERIC_NOP7 -#define GENERIC_NOP5_ATOMIC NOP_DS_PREFIX,GENERIC_NOP4 +/* + * Generic 32bit nops from GAS: + * + * 1: nop + * 2: movl %esi,%esi + * 3: leal 0x0(%esi),%esi + * 4: leal 0x0(%esi,%eiz,1),%esi + * 5: leal %ds:0x0(%esi,%eiz,1),%esi + * 6: leal 0x0(%esi),%esi + * 7: leal 0x0(%esi,%eiz,1),%esi + * 8: leal %ds:0x0(%esi,%eiz,1),%esi + * + * Except 5 and 8, which are DS prefixed 4 and 7 resp, where GAS would emit 2 + * nop instructions. + */ +#define BYTES_NOP1 0x90 +#define BYTES_NOP2 0x89,0xf6 +#define BYTES_NOP3 0x8d,0x76,0x00 +#define BYTES_NOP4 0x8d,0x74,0x26,0x00 +#define BYTES_NOP5 0x3e,BYTES_NOP4 +#define BYTES_NOP6 0x8d,0xb6,0x00,0x00,0x00,0x00 +#define BYTES_NOP7 0x8d,0xb4,0x26,0x00,0x00,0x00,0x00 +#define BYTES_NOP8 0x3e,BYTES_NOP7 -/* Opteron 64bit nops - 1: nop - 2: osp nop - 3: osp osp nop - 4: osp osp osp nop -*/ -#define K8_NOP1 GENERIC_NOP1 -#define K8_NOP2 0x66,K8_NOP1 -#define K8_NOP3 0x66,K8_NOP2 -#define K8_NOP4 0x66,K8_NOP3 -#define K8_NOP5 K8_NOP3,K8_NOP2 -#define K8_NOP6 K8_NOP3,K8_NOP3 -#define K8_NOP7 K8_NOP4,K8_NOP3 -#define K8_NOP8 K8_NOP4,K8_NOP4 -#define K8_NOP5_ATOMIC 0x66,K8_NOP4 +#else -/* K7 nops - uses eax dependencies (arbitrary choice) - 1: nop - 2: movl %eax,%eax - 3: leal (,%eax,1),%eax - 4: leal 0x00(,%eax,1),%eax - 6: leal 0x00000000(%eax),%eax - 7: leal 0x00000000(,%eax,1),%eax -*/ -#define K7_NOP1 GENERIC_NOP1 -#define K7_NOP2 0x8b,0xc0 -#define K7_NOP3 0x8d,0x04,0x20 -#define K7_NOP4 0x8d,0x44,0x20,0x00 -#define K7_NOP5 K7_NOP4,K7_NOP1 -#define K7_NOP6 0x8d,0x80,0,0,0,0 -#define K7_NOP7 0x8D,0x04,0x05,0,0,0,0 -#define K7_NOP8 K7_NOP7,K7_NOP1 -#define K7_NOP5_ATOMIC NOP_DS_PREFIX,K7_NOP4 +/* + * Generic 64bit nops from GAS: + * + * 1: nop + * 2: osp nop + * 3: nopl (%eax) + * 4: nopl 0x00(%eax) + * 5: nopl 0x00(%eax,%eax,1) + * 6: osp nopl 0x00(%eax,%eax,1) + * 7: nopl 0x00000000(%eax) + * 8: nopl 0x00000000(%eax,%eax,1) + */ +#define BYTES_NOP1 0x90 +#define BYTES_NOP2 0x66,BYTES_NOP1 +#define BYTES_NOP3 0x0f,0x1f,0x00 +#define BYTES_NOP4 0x0f,0x1f,0x40,0x00 +#define BYTES_NOP5 0x0f,0x1f,0x44,0x00,0x00 +#define BYTES_NOP6 0x66,BYTES_NOP5 +#define BYTES_NOP7 0x0f,0x1f,0x80,0x00,0x00,0x00,0x00 +#define BYTES_NOP8 0x0f,0x1f,0x84,0x00,0x00,0x00,0x00,0x00 -/* P6 nops - uses eax dependencies (Intel-recommended choice) - 1: nop - 2: osp nop - 3: nopl (%eax) - 4: nopl 0x00(%eax) - 5: nopl 0x00(%eax,%eax,1) - 6: osp nopl 0x00(%eax,%eax,1) - 7: nopl 0x00000000(%eax) - 8: nopl 0x00000000(%eax,%eax,1) - Note: All the above are assumed to be a single instruction. - There is kernel code that depends on this. -*/ -#define P6_NOP1 GENERIC_NOP1 -#define P6_NOP2 0x66,0x90 -#define P6_NOP3 0x0f,0x1f,0x00 -#define P6_NOP4 0x0f,0x1f,0x40,0 -#define P6_NOP5 0x0f,0x1f,0x44,0x00,0 -#define P6_NOP6 0x66,0x0f,0x1f,0x44,0x00,0 -#define P6_NOP7 0x0f,0x1f,0x80,0,0,0,0 -#define P6_NOP8 0x0f,0x1f,0x84,0x00,0,0,0,0 -#define P6_NOP5_ATOMIC P6_NOP5 +#endif /* CONFIG_64BIT */ #ifdef __ASSEMBLY__ #define _ASM_MK_NOP(x) .byte x @@ -94,54 +63,19 @@ #define _ASM_MK_NOP(x) ".byte " __stringify(x) "\n" #endif -#if defined(CONFIG_MK7) -#define ASM_NOP1 _ASM_MK_NOP(K7_NOP1) -#define ASM_NOP2 _ASM_MK_NOP(K7_NOP2) -#define ASM_NOP3 _ASM_MK_NOP(K7_NOP3) -#define ASM_NOP4 _ASM_MK_NOP(K7_NOP4) -#define ASM_NOP5 _ASM_MK_NOP(K7_NOP5) -#define ASM_NOP6 _ASM_MK_NOP(K7_NOP6) -#define ASM_NOP7 _ASM_MK_NOP(K7_NOP7) -#define ASM_NOP8 _ASM_MK_NOP(K7_NOP8) -#define ASM_NOP5_ATOMIC _ASM_MK_NOP(K7_NOP5_ATOMIC) -#elif defined(CONFIG_X86_P6_NOP) -#define ASM_NOP1 _ASM_MK_NOP(P6_NOP1) -#define ASM_NOP2 _ASM_MK_NOP(P6_NOP2) -#define ASM_NOP3 _ASM_MK_NOP(P6_NOP3) -#define ASM_NOP4 _ASM_MK_NOP(P6_NOP4) -#define ASM_NOP5 _ASM_MK_NOP(P6_NOP5) -#define ASM_NOP6 _ASM_MK_NOP(P6_NOP6) -#define ASM_NOP7 _ASM_MK_NOP(P6_NOP7) -#define ASM_NOP8 _ASM_MK_NOP(P6_NOP8) -#define ASM_NOP5_ATOMIC _ASM_MK_NOP(P6_NOP5_ATOMIC) -#elif defined(CONFIG_X86_64) -#define ASM_NOP1 _ASM_MK_NOP(K8_NOP1) -#define ASM_NOP2 _ASM_MK_NOP(K8_NOP2) -#define ASM_NOP3 _ASM_MK_NOP(K8_NOP3) -#define ASM_NOP4 _ASM_MK_NOP(K8_NOP4) -#define ASM_NOP5 _ASM_MK_NOP(K8_NOP5) -#define ASM_NOP6 _ASM_MK_NOP(K8_NOP6) -#define ASM_NOP7 _ASM_MK_NOP(K8_NOP7) -#define ASM_NOP8 _ASM_MK_NOP(K8_NOP8) -#define ASM_NOP5_ATOMIC _ASM_MK_NOP(K8_NOP5_ATOMIC) -#else -#define ASM_NOP1 _ASM_MK_NOP(GENERIC_NOP1) -#define ASM_NOP2 _ASM_MK_NOP(GENERIC_NOP2) -#define ASM_NOP3 _ASM_MK_NOP(GENERIC_NOP3) -#define ASM_NOP4 _ASM_MK_NOP(GENERIC_NOP4) -#define ASM_NOP5 _ASM_MK_NOP(GENERIC_NOP5) -#define ASM_NOP6 _ASM_MK_NOP(GENERIC_NOP6) -#define ASM_NOP7 _ASM_MK_NOP(GENERIC_NOP7) -#define ASM_NOP8 _ASM_MK_NOP(GENERIC_NOP8) -#define ASM_NOP5_ATOMIC _ASM_MK_NOP(GENERIC_NOP5_ATOMIC) -#endif +#define ASM_NOP1 _ASM_MK_NOP(BYTES_NOP1) +#define ASM_NOP2 _ASM_MK_NOP(BYTES_NOP2) +#define ASM_NOP3 _ASM_MK_NOP(BYTES_NOP3) +#define ASM_NOP4 _ASM_MK_NOP(BYTES_NOP4) +#define ASM_NOP5 _ASM_MK_NOP(BYTES_NOP5) +#define ASM_NOP6 _ASM_MK_NOP(BYTES_NOP6) +#define ASM_NOP7 _ASM_MK_NOP(BYTES_NOP7) +#define ASM_NOP8 _ASM_MK_NOP(BYTES_NOP8) #define ASM_NOP_MAX 8 -#define NOP_ATOMIC5 (ASM_NOP_MAX+1) /* Entry for the 5-byte atomic NOP */ #ifndef __ASSEMBLY__ -extern const unsigned char * const *ideal_nops; -extern void arch_init_ideal_nops(void); +extern const unsigned char * const x86_nops[]; #endif #endif /* _ASM_X86_NOPS_H */ |