5.15-stable review patch. If anyone has any objections, please let me know.
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From: Jim Mattson jmattson@google.com
commit 80c883db87d9ffe2d685e91ba07a087b1c246c78 upstream.
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 jmattson@google.com Link: https://lore.kernel.org/r/20231024001636.890236-2-jmattson@google.com [sean: use a macro, rewrite changelog] Signed-off-by: Sean Christopherson seanjc@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/reverse_cpuid.h | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-)
--- a/arch/x86/kvm/reverse_cpuid.h +++ b/arch/x86/kvm/reverse_cpuid.h @@ -97,14 +97,16 @@ static __always_inline void reverse_cpui */ 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_RRSBA_CTRL) - return KVM_X86_FEATURE_RRSBA_CTRL; +#define KVM_X86_TRANSLATE_FEATURE(f) \ + case X86_FEATURE_##f: return KVM_X86_FEATURE_##f
- return x86_feature; + switch (x86_feature) { + KVM_X86_TRANSLATE_FEATURE(SGX1); + KVM_X86_TRANSLATE_FEATURE(SGX2); + KVM_X86_TRANSLATE_FEATURE(RRSBA_CTRL); + default: + return x86_feature; + } }
static __always_inline u32 __feature_leaf(int x86_feature)