Re: [PATCH v2 6/6] kvm: return -EFAULT for writes to !VM_WRITE IO mappings

[sashiko-bot@kernel.org]

> KVM's behavior when the guest writes to a non-writable VMA is inconsistent.
> For regular, page-backed mappings it returns KVM_PFN_ERR_FAULT and thus
> returns -EFAULT to userspace (which is ABI, and relied upon by tests);
> for VM_IO/VM_PFNMAP mappings instead it returns KVM_PFN_ERR_RO_FAULT
> and thus exits to userspace with KVM_EXIT_MMIO.
> 
> This behavior for VM_{IO,PFNMAP} was added by commit bd2fae8da794 ("KVM:
> do not assume PTE is writable after follow_pfn"), and even if it has been
> in place for five years it is unlikely that it is relied upon by userspace,
> since it is inconsistent with KVM itself.  Change hva_to_pfn() to return
> KVM_PFN_ERR_FAULT for all non-writable VMAs, and restrict KVM_EXIT_MMIO
> to the case of an explicitly read-only memslot.
> 
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260804120529.1730187-1-pbonzini@redhat.com?part=6