WARN if the save state size for a valid XCR0-managed sub-leaf is zero, which would indicate a KVM or CPU bug. Add a comment to explain why KVM WARNs so the reader doesn't have to tease out the relevant bits from Intel's SDM and KVM's XCR0/XSS code. Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> --- arch/x86/kvm/cpuid.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index fd9b29aa7abc..424dde41cb5d 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -677,10 +677,17 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function, goto out; do_host_cpuid(&entry[i], function, idx); - if (entry[i].eax == 0) - continue; - if (WARN_ON_ONCE(entry[i].ecx & 1)) + + /* + * The @supported check above should have filtered out + * invalid sub-leafs as well as sub-leafs managed by + * IA32_XSS MSR. Only XCR0-managed sub-leafs should + * reach this point, and they should have a non-zero + * save state size. + */ + if (WARN_ON_ONCE(!entry[i].eax || (entry[i].ecx & 1))) continue; + entry[i].ecx = 0; entry[i].edx = 0; ++*nent; -- 2.24.1
