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From: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>
To: linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev
Cc: Suzuki K Poulose <Suzuki.Poulose@arm.com>,
	Steven Price <steven.price@arm.com>,
	Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	Joey Gouly <joey.gouly@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	"Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>
Subject: [PATCH v2 2/7] KVM: arm64: MTE: Update code comments
Date: Fri, 10 Jan 2025 16:30:18 +0530	[thread overview]
Message-ID: <20250110110023.2963795-3-aneesh.kumar@kernel.org> (raw)
In-Reply-To: <20250110110023.2963795-1-aneesh.kumar@kernel.org>

commit d77e59a8fccd ("arm64: mte: Lock a page for MTE tag
initialisation") updated the locking such the kernel now allows
VM_SHARED mapping with MTE. Update the code comment to reflect this.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 arch/arm64/kvm/mmu.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index c9d46ad57e52..eb8220a409e1 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1391,11 +1391,11 @@ static int get_vma_page_shift(struct vm_area_struct *vma, unsigned long hva)
  * able to see the page's tags and therefore they must be initialised first. If
  * PG_mte_tagged is set, tags have already been initialised.
  *
- * The race in the test/set of the PG_mte_tagged flag is handled by:
- * - preventing VM_SHARED mappings in a memslot with MTE preventing two VMs
- *   racing to santise the same page
- * - mmap_lock protects between a VM faulting a page in and the VMM performing
- *   an mprotect() to add VM_MTE
+ * The race in the test/set of the PG_mte_tagged flag is handled by using
+ * PG_mte_lock and PG_mte_tagged together. if PG_mte_lock is found unset, we can
+ * go ahead and clear the page tags. if PG_mte_lock is found set, then the page
+ * tags are already cleared or there is a parallel tag clearing is going on. We
+ * wait for the parallel tag clear to finish by waiting on PG_mte_tagged bit.
  */
 static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
 			      unsigned long size)
-- 
2.43.0



  parent reply	other threads:[~2025-01-10 11:04 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-01-10 11:00 [PATCH v2 0/7] Add support for NoTagAccess memory attribute Aneesh Kumar K.V (Arm)
2025-01-10 11:00 ` [PATCH v2 1/7] arm64: Update the values to binary from hex Aneesh Kumar K.V (Arm)
2025-01-10 13:11   ` Catalin Marinas
2025-01-10 11:00 ` Aneesh Kumar K.V (Arm) [this message]
2025-01-10 13:11   ` [PATCH v2 2/7] KVM: arm64: MTE: Update code comments Catalin Marinas
2025-01-10 11:00 ` [PATCH v2 3/7] arm64: cpufeature: add Allocation Tag Access Permission (MTE_PERM) feature Aneesh Kumar K.V (Arm)
2025-01-10 13:15   ` Catalin Marinas
2025-01-10 11:00 ` [PATCH v2 4/7] KVM: arm64: MTE: Add KVM_CAP_ARM_MTE_PERM Aneesh Kumar K.V (Arm)
2025-01-10 11:00 ` [PATCH v2 5/7] KVM: arm64: MTE: Use stage-2 NoTagAccess memory attribute if supported Aneesh Kumar K.V (Arm)
2025-01-10 18:20   ` Catalin Marinas
2025-01-11 13:19     ` Aneesh Kumar K.V
2025-01-13 19:09       ` Catalin Marinas
2025-01-13 20:47         ` Peter Collingbourne
2025-01-14  9:55           ` Suzuki K Poulose
2025-01-15 13:15           ` Catalin Marinas
2025-01-28 10:31             ` Aneesh Kumar K.V
2025-01-29 14:38               ` Catalin Marinas
2025-01-10 11:00 ` [PATCH v2 6/7] KVM: arm64: MTE: Nested guest support Aneesh Kumar K.V (Arm)
2025-01-10 11:00 ` [PATCH v2 7/7] KVM: arm64: Split some of the kvm_pgtable_prot bits into separate defines Aneesh Kumar K.V (Arm)

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