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Fri, 05 Jun 2026 16:18:31 +0000 Date: Fri, 05 Jun 2026 17:18:30 +0100 Message-ID: <86wlwdt0yx.wl-maz@kernel.org> From: Marc Zyngier To: Ard Biesheuvel Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, Ard Biesheuvel , Kevin Brodsky , Mark Brown , stable@vger.kernel.org Subject: Re: [PATCH v2 4/5] KVM: arm64: Omit tag sync on stage-2 mappings of the zero page In-Reply-To: <20260604151151.150377-11-ardb+git@google.com> References: <20260604151151.150377-7-ardb+git@google.com> <20260604151151.150377-11-ardb+git@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: ardb+git@google.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, ardb@kernel.org, kevin.brodsky@arm.com, broonie@kernel.org, stable@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, 04 Jun 2026 16:11:56 +0100, Ard Biesheuvel wrote: > > From: Ard Biesheuvel > > Commit > > f620d66af316 ("arm64: mte: Do not flag the zero page as PG_mte_tagged") > > removed the PG_mte_tagged flag from the zero page, but missed a KVM code > path that may set this flag on the zero page when it is used in a > stage-2 CoW mapping of anonymous memory. > > So disregard the zero page explicitly in sanitise_mte_tags(). > > Fixes: f620d66af316 ("arm64: mte: Do not flag the zero page as PG_mte_tagged") > Cc: # 5.10.x > Suggested-by: Catalin Marinas > Signed-off-by: Ard Biesheuvel > --- > arch/arm64/kvm/mmu.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index d089c107d9b7..445d6cf035c9 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1479,6 +1479,11 @@ static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn, > if (!kvm_has_mte(kvm)) > return; > > + if (is_zero_pfn(pfn)) { > + WARN_ON_ONCE(nr_pages != 1); > + return; > + } > + > if (folio_test_hugetlb(folio)) { > /* Hugetlb has MTE flags set on head page only */ > if (folio_try_hugetlb_mte_tagging(folio)) { Reviewed-by: Marc Zyngier M. -- Without deviation from the norm, progress is not possible.