linux-kernel - [PATCH] KVM: arm64: Release mmap_lock when using VM

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Message-Id: <20211005122031.809857-1-qperret@google.com>
Date:   Tue,  5 Oct 2021 13:20:31 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Steven Price <steven.price@....com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Cc:     kernel-team@...roid.com, Quentin Perret <qperret@...gle.com>
Subject: [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 <qperret@...gle.com>
---
 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