From 80c883db87d9ffe2d685e91ba07a087b1c246c78 Mon Sep 17 00:00:00 2001 From: Jim Mattson Date: Mon, 23 Oct 2023 17:16:36 -0700 Subject: KVM: x86: Use a switch statement and macros in __feature_translate() Use a switch statement with macro-generated case statements to handle translating feature flags in order to reduce the probability of runtime errors due to copy+paste goofs, to make compile-time errors easier to debug, and to make the code more readable. E.g. the compiler won't directly generate an error for duplicate if statements if (x86_feature == X86_FEATURE_SGX1) return KVM_X86_FEATURE_SGX1; else if (x86_feature == X86_FEATURE_SGX2) return KVM_X86_FEATURE_SGX1; and so instead reverse_cpuid_check() will fail due to the untranslated entry pointing at a Linux-defined leaf, which provides practically no hint as to what is broken arch/x86/kvm/reverse_cpuid.h:108:2: error: call to __compiletime_assert_450 declared with 'error' attribute: BUILD_BUG_ON failed: x86_leaf == CPUID_LNX_4 BUILD_BUG_ON(x86_leaf == CPUID_LNX_4); ^ whereas duplicate case statements very explicitly point at the offending code: arch/x86/kvm/reverse_cpuid.h:125:2: error: duplicate case value '361' KVM_X86_TRANSLATE_FEATURE(SGX2); ^ arch/x86/kvm/reverse_cpuid.h:124:2: error: duplicate case value '360' KVM_X86_TRANSLATE_FEATURE(SGX1); ^ And without macros, the opposite type of copy+paste goof doesn't generate any error at compile-time, e.g. this yields no complaints: case X86_FEATURE_SGX1: return KVM_X86_FEATURE_SGX1; case X86_FEATURE_SGX2: return KVM_X86_FEATURE_SGX1; Note, __feature_translate() is forcibly inlined and the feature is known at compile-time, so the code generation between an if-elif sequence and a switch statement should be identical. Signed-off-by: Jim Mattson Link: https://lore.kernel.org/r/20231024001636.890236-2-jmattson@google.com [sean: use a macro, rewrite changelog] Signed-off-by: Sean Christopherson --- arch/x86/kvm/reverse_cpuid.h | 27 +++++++++++++-------------- 1 file changed, 13 insertions(+), 14 deletions(-) (limited to 'arch/x86/kvm/reverse_cpuid.h') diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h index 17007016d8b5..aadefcaa9561 100644 --- a/arch/x86/kvm/reverse_cpuid.h +++ b/arch/x86/kvm/reverse_cpuid.h @@ -116,20 +116,19 @@ static __always_inline void reverse_cpuid_check(unsigned int x86_leaf) */ static __always_inline u32 __feature_translate(int x86_feature) { - if (x86_feature == X86_FEATURE_SGX1) - return KVM_X86_FEATURE_SGX1; - else if (x86_feature == X86_FEATURE_SGX2) - return KVM_X86_FEATURE_SGX2; - else if (x86_feature == X86_FEATURE_SGX_EDECCSSA) - return KVM_X86_FEATURE_SGX_EDECCSSA; - else if (x86_feature == X86_FEATURE_CONSTANT_TSC) - return KVM_X86_FEATURE_CONSTANT_TSC; - else if (x86_feature == X86_FEATURE_PERFMON_V2) - return KVM_X86_FEATURE_PERFMON_V2; - else if (x86_feature == X86_FEATURE_RRSBA_CTRL) - return KVM_X86_FEATURE_RRSBA_CTRL; - - return x86_feature; +#define KVM_X86_TRANSLATE_FEATURE(f) \ + case X86_FEATURE_##f: return KVM_X86_FEATURE_##f + + switch (x86_feature) { + KVM_X86_TRANSLATE_FEATURE(SGX1); + KVM_X86_TRANSLATE_FEATURE(SGX2); + KVM_X86_TRANSLATE_FEATURE(SGX_EDECCSSA); + KVM_X86_TRANSLATE_FEATURE(CONSTANT_TSC); + KVM_X86_TRANSLATE_FEATURE(PERFMON_V2); + KVM_X86_TRANSLATE_FEATURE(RRSBA_CTRL); + default: + return x86_feature; + } } static __always_inline u32 __feature_leaf(int x86_feature) -- cgit v1.2.3