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KVM: x86: Use a switch statement and macros in __feature_translate()
commit 80c883db87
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>
This commit is contained in:
parent
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commit
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1 changed files with 9 additions and 7 deletions
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@ -97,14 +97,16 @@ static __always_inline void reverse_cpuid_check(unsigned int x86_leaf)
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*/
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static __always_inline u32 __feature_translate(int x86_feature)
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{
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if (x86_feature == X86_FEATURE_SGX1)
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return KVM_X86_FEATURE_SGX1;
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else if (x86_feature == X86_FEATURE_SGX2)
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return KVM_X86_FEATURE_SGX2;
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else if (x86_feature == X86_FEATURE_RRSBA_CTRL)
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return KVM_X86_FEATURE_RRSBA_CTRL;
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#define KVM_X86_TRANSLATE_FEATURE(f) \
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case X86_FEATURE_##f: return KVM_X86_FEATURE_##f
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return x86_feature;
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switch (x86_feature) {
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KVM_X86_TRANSLATE_FEATURE(SGX1);
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KVM_X86_TRANSLATE_FEATURE(SGX2);
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KVM_X86_TRANSLATE_FEATURE(RRSBA_CTRL);
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default:
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return x86_feature;
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}
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}
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static __always_inline u32 __feature_leaf(int x86_feature)
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