[PATCH v3 6/7] KVM: arm64: permit all VM_MTE_ALLOWED mappings with MTE enabled

From: Peter Collingbourne <pcc@google.com>
To: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu
Cc: kvm@vger.kernel.org, Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Steven Price <steven.price@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Peter Collingbourne <pcc@google.com>,
	Evgenii Stepanov <eugenis@google.com>
Subject: [PATCH v3 6/7] KVM: arm64: permit all VM_MTE_ALLOWED mappings with MTE enabled
Date: Wed, 10 Aug 2022 12:30:32 -0700	[thread overview]
Message-ID: <20220810193033.1090251-7-pcc@google.com> (raw)
In-Reply-To: <20220810193033.1090251-1-pcc@google.com>

Certain VMMs such as crosvm have features (e.g. sandboxing) that depend
on being able to map guest memory as MAP_SHARED. The current restriction
on sharing MAP_SHARED pages with the guest is preventing the use of
those features with MTE. Now that the races between tasks concurrently
clearing tags on the same page have been fixed, remove this restriction.

Signed-off-by: Peter Collingbourne <pcc@google.com>
---
 arch/arm64/kvm/mmu.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index d54be80e31dd..fc65dc20655d 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1075,14 +1075,6 @@ static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
 
 static bool kvm_vma_mte_allowed(struct vm_area_struct *vma)
 {
-	/*
-	 * VM_SHARED mappings are not allowed with MTE to avoid races
-	 * when updating the PG_mte_tagged page flag, see
-	 * sanitise_mte_tags for more details.
-	 */
-	if (vma->vm_flags & VM_SHARED)
-		return false;
-
 	return vma->vm_flags & VM_MTE_ALLOWED;
 }
 
-- 
2.37.1.559.g78731f0fdb-goog

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