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AJvYcCWXHsFUkge3p3ogBhlMkW1IN9JEkPAJgv7FBcBlw423vthexP0haAst4hzBaIfsqMqiH3YUTn8jBfAKIdUtvG5pJh8= X-Gm-Message-State: AOJu0YwXgNGKuqEerkuzTtzlPMaV6ovl3KiO7X6+d/wqmBRH6CVd5WsH 8Qdky+6UAV4wP6wja3ZlBsWdEEv8Tfe2wS1AhvbF4TUT5QSvODtDO0dOmu94BFGVJWSTSId9NPT r6xGZCAu+6LZQrSx9aKdMOUD02OdvIq3/eSyO X-Google-Smtp-Source: AGHT+IH9sSY76fFvumrBUCB5IOWf40dprm49al51d9C63r/bzJh0mJ4NGK5So9vqJF4lfC7MlLaL31EdoOvAUHGh1YY= X-Received: by 2002:ac8:7357:0:b0:437:c52f:cd6a with SMTP id q23-20020ac87357000000b00437c52fcd6amr69580qtp.8.1713560123419; Fri, 19 Apr 2024 13:55:23 -0700 (PDT) MIME-Version: 1.0 References: <20240401232946.1837665-1-jthoughton@google.com> <20240401232946.1837665-6-jthoughton@google.com> In-Reply-To: From: James Houghton Date: Fri, 19 Apr 2024 13:54:47 -0700 Message-ID: Subject: Re: [PATCH v3 5/7] KVM: x86: Participate in bitmap-based PTE aging To: David Matlack 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 6BB2F140018 X-Stat-Signature: ofk1gufnic3knwrxraqpoaewpa1hnctt X-HE-Tag: 1713560124-907383 X-HE-Meta: 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 0Vg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Apr 12, 2024 at 1:44=E2=80=AFPM David Matlack = wrote: > > 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. Indeed, thanks. I'll make sure to build with CONFIG_LOCKDEP for the future versions and check for errors. > > 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. I'll add the macro / function to do the lockless walk of tdp_mmu_roots and explain why it is safe. Thanks for pointing out this big mistake. > [1] https://lore.kernel.org/kvmarm/ZItX64Bbx5vdjo9M@google.com/