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[34.125.73.210]) by smtp.gmail.com with ESMTPSA id lr31-20020a056a00739f00b006ecfe1c9630sm3368108pfb.92.2024.04.12.13.44.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Apr 2024 13:44:45 -0700 (PDT) Date: Fri, 12 Apr 2024 13:44:41 -0700 From: David Matlack To: James Houghton Cc: Andrew Morton , Paolo Bonzini , Yu Zhao , Marc Zyngier , Oliver Upton , Sean Christopherson , Jonathan Corbet , James Morse , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Shaoqin Huang , Gavin Shan , Ricardo Koller , Raghavendra Rao Ananta , Ryan Roberts , David Rientjes , Axel Rasmussen , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v3 5/7] KVM: x86: Participate in bitmap-based PTE aging Message-ID: References: <20240401232946.1837665-1-jthoughton@google.com> <20240401232946.1837665-6-jthoughton@google.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240401232946.1837665-6-jthoughton@google.com> On 2024-04-01 11:29 PM, James Houghton wrote: > Only handle the TDP MMU case for now. In other cases, if a bitmap was > not provided, fallback to the slowpath that takes mmu_lock, or, if a > bitmap was provided, inform the caller that the bitmap is unreliable. I think this patch will trigger a lockdep assert in kvm_tdp_mmu_age_gfn_range kvm_tdp_mmu_handle_gfn for_each_tdp_mmu_root __for_each_tdp_mmu_root kvm_lockdep_assert_mmu_lock_held ... because it walks tdp_mmu_roots without holding mmu_lock. Yu's patch[1] added a lockless walk to the TDP MMU. We'd need something similar here and also update the comment above tdp_mmu_roots describing how tdp_mmu_roots can be read locklessly. [1] https://lore.kernel.org/kvmarm/ZItX64Bbx5vdjo9M@google.com/