Re: [PATCH 43/60] kvm: x86: Move CPUID state to struct kvm_vcpu_arch_common

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Sharing `cpuid_entries` and `cpuid_dynamic_bits_dirty` across planes causes dynamic CPUID bits to reflect the architectural state of the wrong plane, leading to cross-plane state corruption.
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commit 696f84e84e21cbabab51dbf9bde76487e123b217
Author: Joerg Roedel <joerg.roedel@amd.com>

The CPUID state is shared across all planes, so move it to struct
kvm_vcpu_arch_common.

This commit moves cpuid state tracking from the per-plane kvm_vcpu_arch
to the shared kvm_vcpu_arch_common structure.

> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index e69156b54cff..6d948d63306c 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
[ ... ]
> @@ -2089,10 +2094,11 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
>  	       u32 *ecx, u32 *edx, bool exact_only)
>  {
>  	u32 orig_function = *eax, function = *eax, index = *ecx;
> +	struct kvm_vcpu_common *common = vcpu->common;
>  	struct kvm_cpuid_entry2 *entry;
>  	bool exact, used_max_basic = false;
>  
> -	if (vcpu->arch.cpuid_dynamic_bits_dirty)
> +	if (common->arch.cpuid_dynamic_bits_dirty)
>  		kvm_update_cpuid_runtime(vcpu);
>  
>  	entry = kvm_find_cpuid_entry_index(vcpu, function, index);

[Severity: High]
Will this cause planes to observe dynamic cpuid bits from other planes?

Since cpuid_entries and cpuid_dynamic_bits_dirty are now shared across all
planes in vcpu->common->arch, kvm_update_cpuid_runtime() will modify the
shared array using per-plane state like vcpu->arch.cr4 and vcpu->arch.xcr0.

When kvm_update_cpuid_runtime() completes, it clears the shared dirty flag.
If a different plane later calls kvm_cpuid(), won't it see the dirty flag
as cleared and bypass its own update? This seems like it would return the
other plane's cached dynamic bits and xstate sizes.

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Sashiko AI review · https://sashiko.dev/#/patchset/20260608144252.351443-1-joro@8bytes.org?part=43