[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v3 07/15] x86/alternative: support "not feature" and ALTERNATIVE_TERNARY
On Thu, Dec 17, 2020 at 10:31:25AM +0100, Juergen Gross wrote: > Instead of only supporting to modify instructions when a specific > feature is set, support doing so for the case a feature is not set. > > As today a feature is specified using a 16 bit quantity and the highest > feature number in use is around 600, using a negated feature number for > specifying the inverted case seems to be appropriate. > > ALTERNATIVE "default_instr", "patched_instr", ~FEATURE_NR > > will start with "default_instr" and patch that with "patched_instr" in > case FEATURE_NR is not set. > > Using that add ALTERNATIVE_TERNARY: > > ALTERNATIVE_TERNARY "default_instr", FEATURE_NR, > "feature_on_instr", "feature_off_instr" > > which will start with "default_instr" and at patch time will, depending > on FEATURE_NR being set or not, patch that with either > "feature_on_instr" or "feature_off_instr". How about an even simpler one (only build-tested): --- diff --git a/arch/x86/include/asm/alternative-asm.h b/arch/x86/include/asm/alternative-asm.h index 464034db299f..d52b423d3cab 100644 --- a/arch/x86/include/asm/alternative-asm.h +++ b/arch/x86/include/asm/alternative-asm.h @@ -109,6 +109,9 @@ .popsection .endm +#define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr1, newinstr2) \ + ALTERNATIVE_2 oldinstr, newinstr1, feature, newinstr2, X86_FEATURE_TERNARY + #endif /* __ASSEMBLY__ */ #endif /* _ASM_X86_ALTERNATIVE_ASM_H */ diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h index 13adca37c99a..f170cbe89539 100644 --- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -175,6 +175,9 @@ static inline int alternatives_text_reserved(void *start, void *end) ALTINSTR_REPLACEMENT(newinstr2, feature2, 2) \ ".popsection\n" +#define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr1, newinstr2) \ + ALTERNATIVE_2(oldinstr, newinstr1, feature, newinstr2, X86_FEATURE_TERNARY) + #define ALTERNATIVE_3(oldinsn, newinsn1, feat1, newinsn2, feat2, newinsn3, feat3) \ OLDINSTR_3(oldinsn, 1, 2, 3) \ ".pushsection .altinstructions,\"a\"\n" \ @@ -206,6 +209,9 @@ static inline int alternatives_text_reserved(void *start, void *end) #define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \ asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory") +#define alternative_ternary(oldinstr, feature, newinstr1, newinstr2) \ + asm_inline volatile(ALTERNATIVE_TERNARY(oldinstr, feature, newinstr1, newinstr2) ::: "memory") + /* * Alternative inline assembly with input. * diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index 84b887825f12..cc634db0b91f 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -108,7 +108,7 @@ #define X86_FEATURE_EXTD_APICID ( 3*32+26) /* Extended APICID (8 bits) */ #define X86_FEATURE_AMD_DCM ( 3*32+27) /* AMD multi-node processor */ #define X86_FEATURE_APERFMPERF ( 3*32+28) /* P-State hardware coordination feedback capability (APERF/MPERF MSRs) */ -/* free ( 3*32+29) */ +#define X86_FEATURE_TERNARY ( 3*32+29) /* "" Synthetic bit for ALTERNATIVE_TERNARY() */ #define X86_FEATURE_NONSTOP_TSC_S3 ( 3*32+30) /* TSC doesn't stop in S3 state */ #define X86_FEATURE_TSC_KNOWN_FREQ ( 3*32+31) /* TSC has known frequency */ diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 8d778e46725d..2cb29d4d8dd9 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -393,7 +393,7 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, replacement = (u8 *)&a->repl_offset + a->repl_offset; BUG_ON(a->instrlen > sizeof(insn_buff)); BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32); - if (!boot_cpu_has(a->cpuid)) { + if (!boot_cpu_has(a->cpuid) && (a->cpuid != X86_FEATURE_TERNARY)) { if (a->padlen > 1) optimize_nops(a, instr); -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
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