[PATCH] KVM: arm64: Release mmap_lock when using VM_SHARED with MTE

VM_SHARED mappings are currently forbidden in a memslot with MTE to
prevent two VMs racing to sanitise the same page. However, this check
is performed while holding current->mm's mmap_lock, but fails to release
it. Fix this by releasing the lock when needed.

Fixes: ea7fc1bb1cd1 ("KVM: arm64: Introduce MTE VM feature")
Signed-off-by: Quentin Perret <redacted>
---
 arch/arm64/kvm/mmu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 1a94a7ca48f2..69bd1732a299 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c

@@ -1529,8 +1529,10 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 		 * when updating the PG_mte_tagged page flag, see
 		 * sanitise_mte_tags for more details.
 		 */
-		if (kvm_has_mte(kvm) && vma->vm_flags & VM_SHARED)
-			return -EINVAL;
+		if (kvm_has_mte(kvm) && vma->vm_flags & VM_SHARED) {
+			ret = -EINVAL;
+			break;
+		}
 
 		if (vma->vm_flags & VM_PFNMAP) {
 			/* IO region dirty page logging not allowed */

-- 
2.33.0.800.g4c38ced690-goog


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On Tue, 5 Oct 2021 13:20:31 +0100, Quentin Perret wrote:

VM_SHARED mappings are currently forbidden in a memslot with MTE to
prevent two VMs racing to sanitise the same page. However, this check
is performed while holding current->mm's mmap_lock, but fails to release
it. Fix this by releasing the lock when needed.

Applied to fixes, thanks!

[1/1] KVM: arm64: Release mmap_lock when using VM_SHARED with MTE
      commit: 6e6a8ef088e1222cb1250942f51ad9c1ab219ab2

Cheers,

	M.
-- 
Without deviation from the norm, progress is not possible.



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