Re: [PATCH v6 6/9] KVM: guest_memfd: Only "prepare" folios for private pages

[Xiaoyao Li]

On 7/24/2026 5:08 AM, Sean Christopherson wrote:
> From: Ackerley Tng <ackerleytng@xxxxxxxxxx>
>
> When getting a guest_memfd pfn, prepare the folio, i.e. convert its pages
> to private, if and only if the page is actually private.  The misnamed
> prepare() hook exists specifically to allow x86's SNP to assign pages to
> the owning VM in the RMP when mapping private memory into a guest.
>
> Guarding the call will allow renaming the prepare() hook to better reflect
> its role, without creating a semantic mess, and will become a hard
> requirement once in-place conversion is supported, i.e. when CoCo VMs
> support SHARED guest_memfd pages.
>
> For all intents, no functional change intended (the sole arch hook is a nop
> for SHARED memory).
>
> Suggested-by: Michael Roth <michael.roth@xxxxxxx>
> Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>
> [sean: rewrite changelog to fit the context]
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>

The rewritten the changelog read better and clearer!

Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>

> ---
>   virt/kvm/guest_memfd.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index e9d61410e5fb..f64cd87ec8b0 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -814,7 +814,8 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
>   		folio_mark_uptodate(folio);
>   	}
>   
> -	r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio);
> +	if (kvm_gmem_is_private_mem(file_inode(file), index))
> +		r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio);
>   
>   	folio_unlock(folio);
>