Re: [PATCH v2 4/4] KVM: selftests: Check VMPTRLD with active eVMCS

[Sean Christopherson <seanjc@google.com>]

On Tue, Aug 18, 2026, Sean Christopherson wrote:
> On Tue, Aug 18, 2026, sashiko-bot@kernel.org wrote:
> > > +	asm volatile(KVM_ASM_SAFE("vmptrld %[pa]")
> > > +		     "\n\tsetna %[failed]"
> > 
> > [Severity: Medium]
> > Will this setna instruction incorrectly evaluate CPU flags?
> > 
> > The KVM_ASM_SAFE macro executes xor %%r9, %%r9 on its success path, which
> > unconditionally clears the Carry Flag (CF=0) and sets the Zero Flag (ZF=1).
> 
> Shame on me, I should know better after dealing with ba5ca5e5e6a1 ("x86/retpoline:
> Don't clobber RFLAGS during srso_safe_ret()").
> 
> Untested, but I think the fix is simply:
> 
> diff --git tools/testing/selftests/kvm/include/x86/processor.h tools/testing/selftests/kvm/include/x86/processor.h
> index 6e6f70035508..119715ffe93f 100644
> --- tools/testing/selftests/kvm/include/x86/processor.h
> +++ tools/testing/selftests/kvm/include/x86/processor.h
> @@ -1318,7 +1318,7 @@ gva_t vm_alloc_stack(struct kvm_vm *vm, int nr_pages);
>         "lea 1f(%%rip), %%r10\n\t"                              \
>         "lea 2f(%%rip), %%r11\n\t"                              \
>         fep "1: " insn "\n\t"                                   \
> -       "xor %%r9, %%r9\n\t"                                    \
> +       "mov $0, %%r9\n\t"                                      \
>         "2:\n\t"                                                \
>         "mov  %%r9b, %[vector]\n\t"                             \
>         "mov  %%r10, %[error_code]\n\t"

Vitaly, I'll send a v3 of this series with a rather large pile of additional
selftests changes.  As often seems to be the case, my desire validate a simple
fix has snowballed...