On Wed, 2022-11-23 at 00:20 +0000, David Woodhouse wrote:
> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
>
> In the case where a GPC is refreshed to a different location within the
> same page, we didn't bother to update it. Mostly we don't need to, but
> since the ->khva field also includes the offset within the page, that
> does have to be updated.
>
> Fixes: 982ed0de4753 ("KVM: Reinstate gfn_to_pfn_cache with invalidation support")
Hm, wait. That commit wasn't actually broken because at that point the
page offset was included in the uhva too, so the uhva *did* change and
we'd (gratuitously) take the slower path through hva_to_pfn_retry()
when the GPA moved within the same page.
So I think this should actually be:
Fixes: 3ba2c95ea180 ("KVM: Do not incorporate page offset into gfn=>pfn cache user address")
Which means it's only relevant back to v6.0 stable, not all the way
back to v5.17.
> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> Reviewed-by: Paul Durrant <paul@xxxxxxx>
> Cc: stable@xxxxxxxxxx
>
> ---
> virt/kvm/pfncache.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
> index bd4a46aee384..5f83321bfd2a 100644
> --- a/virt/kvm/pfncache.c
> +++ b/virt/kvm/pfncache.c
> @@ -297,7 +297,12 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
> if (!gpc->valid || old_uhva != gpc->uhva) {
> ret = hva_to_pfn_retry(kvm, gpc);
> } else {
> - /* If the HVA→PFN mapping was already valid, don't unmap it. */
> + /*
> + * If the HVA→PFN mapping was already valid, don't unmap it.
> + * But do update gpc->khva because the offset within the page
> + * may have changed.
> + */
> + gpc->khva = old_khva + page_offset;
> old_pfn = KVM_PFN_ERR_FAULT;
> old_khva = NULL;
> ret = 0;
>
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