On Wed, Jul 31, 2024, Alex Bennée wrote: > Sean Christopherson <seanjc@xxxxxxxxxx> writes: > > > Put the page reference acquired by gfn_to_pfn_prot() if > > kvm_vm_ioctl_mte_copy_tags() runs into ZONE_DEVICE memory. KVM's less- > > than-stellar heuristics for dealing with pfn-mapped memory means that KVM > > can get a page reference to ZONE_DEVICE memory. > > > > Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest") > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > > --- > > arch/arm64/kvm/guest.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c > > index 11098eb7eb44..e1f0ff08836a 100644 > > --- a/arch/arm64/kvm/guest.c > > +++ b/arch/arm64/kvm/guest.c > > @@ -1059,6 +1059,7 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, > > page = pfn_to_online_page(pfn); > > if (!page) { > > /* Reject ZONE_DEVICE memory */ > > + kvm_release_pfn_clean(pfn); > > I guess this gets renamed later in the series. > > However my main comment is does lack of page always mean a ZONE_DEVICE? Nope. > Looking at pfn_to_online_page() I see a bunch of other checks first. Why > isn't it that functions responsibility to clean up after itself if its > returning NULLs? pfn_to_online_page() is more strict than gfn_to_pfn_prot(). At least in theory, gfn_to_pfn_prot() could return a pfn that has an associated "struct page", with a reference held to said page. But for that same pfn, pfn_to_online_page() could return NULL, in which case KVM needs to put the reference it acquired via gfn_to_pfn_prot().