On 07/08/2024 15:15, Catalin Marinas wrote:

On Fri, Jul 26, 2024 at 04:51:10PM -0700, Sean Christopherson wrote:

quoted

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@google.com>
---
 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);
 			ret = -EFAULT;
 			goto out;
 		}

This patch makes sense irrespective of whether the above pfn is a
ZONE_DEVICE or not. gfn_to_pfn_prot() increased the page refcount via
GUP, so it must be released before bailing out of this loop.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Yep, as Catalin says, this is an 'obviously' correct fix - the reference
needs releasing before bailing out. The comment there is perhaps
misleading - it's not just ZONE_DEVICE memory that will be rejected, but
this is the case that was in my mind when I wrote it. Although clearly I
wasn't thinking hard enough when writing the code in the first place... ;)

Reviewed-by: Steven Price <steven.price@arm.com>

Thanks,

Steve