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AJvYcCUKAXA+VvoVM50UPYA+P1EfCBNWt+2lGsx88aT1P/cwENEA+vX8RBejysPYSeBj72XieOBU64j2LA==@kvack.org X-Gm-Message-State: AOJu0YxBkWOGHsCadtJetyPmjxfwSLyE5lULezz6XE1USachkUTzMz4c UYiM4U/ocGWFXBLOnKTxnou15Sd8BUil+X7olyJPdTjz3m/Glq9Wh/M7HHnVOQoBYGQZxBcvLQo KV33AxtR+mL9BCElYtuEYrt1QN5QRLxqxgpjf X-Google-Smtp-Source: AGHT+IFii9QgwJ7X6I4kq0clALv2ZlfTWM+Ez0PZcdvnVsO0zqwYPfgk8ziwPN23MIImR0+NDVcsRZ7OngewarYkwr4= X-Received: by 2002:a05:690c:368f:b0:6db:e03f:7c39 with SMTP id 00721157ae682-6e21d833401mr46817427b3.16.1727315743978; Wed, 25 Sep 2024 18:55:43 -0700 (PDT) MIME-Version: 1.0 References: <20240926013506.860253-1-jthoughton@google.com> <20240926013506.860253-5-jthoughton@google.com> In-Reply-To: <20240926013506.860253-5-jthoughton@google.com> From: James Houghton Date: Wed, 25 Sep 2024 18:55:07 -0700 Message-ID: Subject: Re: [PATCH v7 04/18] KVM: x86/mmu: Relax locking for kvm_test_age_gfn and kvm_age_gfn To: Sean Christopherson , Paolo Bonzini Cc: Andrew Morton , David Matlack , David Rientjes , Jason Gunthorpe , Jonathan Corbet , Marc Zyngier , Oliver Upton , Wei Xu , Yu Zhao , Axel Rasmussen , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 29483180006 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: ac1u3w9iwhfhqpjguqotaitx3kfrfnxj X-HE-Tag: 1727315744-740061 X-HE-Meta: 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 gVE/ygiN rKh0zNaEi1aoiNkswcGnl6twQ8boA3lw0A4WeGwFCjO7d/E5Ss3iux6xVPD+QhrcNHzzvLgPUuZ9ZuXaQG5h0SgSD9pk1oniqTt3Zc65pt2Awn3gilNyEzZhP/EIClCTgrAOj1Qp5MSWwQZ8cbIhurWeyCuzIcx10CUJLbBlAieTvytzRgyRo5uelL2Q8+Tgy8vIXjJU+bxIUQdD4ajAvLOzJg9rXbseBY2s8GDXyfDC7A3OAnuLt7vT4HBSPR914aknd8gs8ZudOTdtUXq1fQlyCVdBP2AkUc0r4 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000210, 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 Wed, Sep 25, 2024 at 6:35=E2=80=AFPM James Houghton wrote: > > Walk the TDP MMU in an RCU read-side critical section without holding > mmu_lock when harvesting and potentially updating age information on > sptes. This requires a way to do RCU-safe walking of the tdp_mmu_roots; > do this with a new macro. The PTE modifications are now done atomically, > and kvm_tdp_mmu_spte_need_atomic_write() has been updated to account for > the fact that kvm_age_gfn can now lockless update the accessed bit and > the W/R/X bits). > > If the cmpxchg for marking the spte for access tracking fails, leave it > as is and treat it as if it were young, as if the spte is being actively > modified, it is most likely young. > > Harvesting age information from the shadow MMU is still done while > holding the MMU write lock. > > Suggested-by: Yu Zhao > Signed-off-by: James Houghton Oh no! I have left off David Matlack's Reviewed-bys[1, 2] from this patch and from patch 2[3], and I failed to apply his comment suggestion on this patch like I said I would. Sorry David, I have fixed up my tree now. [1]: https://lore.kernel.org/linux-mm/ZqJ_xANKf3bNcaHM@google.com/ [2]: https://lore.kernel.org/linux-mm/ZqKUefN3HgBQQkuA@google.com/ [3]: https://lore.kernel.org/kvm/20240926013506.860253-3-jthoughton@google.= com/