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SubjectRe: [PATCH 06/61] KVM: x86: Move CPUID 0xD.1 handling out of the index>0 loop
Date
Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Mov the sub-leaf 1 handling for CPUID 0xD out of the index>0 loop so
> that the loop only handles index>2. Sub-leafs 2+ have identical
> semantics, whereas sub-leaf 1 is effectively a feature sub-leaf.
>
> Moving sub-leaf 1 out of the loop does duplicate a bit of code, but
> the nent/maxnent code will be consolidated in a future patch, and
> duplicating the clear of ECX/EDX is arguably a good thing as the reasons
> for clearing said registers are completely different.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/cpuid.c | 37 ++++++++++++++++++++++---------------
> 1 file changed, 22 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index e5cf1e0cf84a..fc8540596386 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -653,26 +653,33 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
> if (!supported)
> break;
>
> - for (idx = 1, i = 1; idx < 64; ++idx) {
> + if (*nent >= maxnent)
> + goto out;
> +
> + do_host_cpuid(&entry[1], function, 1);
> + ++*nent;
> +
> + entry[1].eax &= kvm_cpuid_D_1_eax_x86_features;
> + cpuid_mask(&entry[1].eax, CPUID_D_1_EAX);
> + if (entry[1].eax & (F(XSAVES)|F(XSAVEC)))
> + entry[1].ebx = xstate_required_size(supported, true);
> + else
> + entry[1].ebx = 0;
> + /* Saving XSS controlled state via XSAVES isn't supported. */
> + entry[1].ecx = 0;
> + entry[1].edx = 0;
> +
> + for (idx = 2, i = 2; idx < 64; ++idx) {
> u64 mask = ((u64)1 << idx);
> +
> if (*nent >= maxnent)
> goto out;
>
> do_host_cpuid(&entry[i], function, idx);
> - if (idx == 1) {
> - entry[i].eax &= kvm_cpuid_D_1_eax_x86_features;
> - cpuid_mask(&entry[i].eax, CPUID_D_1_EAX);
> - entry[i].ebx = 0;
> - if (entry[i].eax & (F(XSAVES)|F(XSAVEC)))
> - entry[i].ebx =
> - xstate_required_size(supported,
> - true);
> - } else {
> - if (entry[i].eax == 0 || !(supported & mask))
> - continue;
> - if (WARN_ON_ONCE(entry[i].ecx & 1))
> - continue;
> - }
> + if (entry[i].eax == 0 || !(supported & mask))
> + continue;
> + if (WARN_ON_ONCE(entry[i].ecx & 1))
> + continue;
> entry[i].ecx = 0;
> entry[i].edx = 0;
> ++*nent;

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

--
Vitaly

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