Re: [PATCH 20/24] KVM: x86/mmu: Do not prefetch sptes on gfns backed by memory attributes

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Skipping SPTE prefetch for pages with memory attributes leaks the `struct page` reference.
--

--- Patch [20]: [PATCH 20/24] KVM: x86/mmu: Do not prefetch sptes on gfns backed by memory attributes ---
commit f42ac0f993cf93f62265ecaa532948b8790213ce
Author: Nicolas Saenz Julienne <nsaenz@amazon.com>

KVM: x86/mmu: Do not prefetch sptes on gfns backed by memory attributes
    
This commit modifies KVM's MMU prefetching to check for memory attributes on
each GFN. If memory protections are applied to a GFN, the code skips
prefetching the SPTE for that page.

> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 59c2a04f5648c..8e85f672a08d5 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3156,6 +3156,9 @@ static bool kvm_mmu_prefetch_sptes(struct kvm_vcpu *vcpu, gfn_t gfn, u64 *sptep,
>  		return false;
>  
>  	for (i = 0; i < nr_pages; i++, gfn++, sptep++) {
> +		if (kvm_get_memory_attributes(vcpu->kvm, gfn))
> +			continue;
> +

[Severity: High]
Does this leak the struct page reference?

Earlier in kvm_mmu_prefetch_sptes(), kvm_prefetch_pages() populates the
pages[] array, which elevates the reference count for each page. By using
continue here, the loop skips over the required cleanup call at the bottom
of the loop:

    kvm_release_page_dirty(pages[i]);

Should this code release the page before continuing to the next iteration?

>  		mmu_set_spte(vcpu, slot, sptep, access, gfn,
>  			     page_to_pfn(pages[i]), NULL);
>

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260716181456.402786-1-pbonzini@redhat.com?part=20