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[47.54.130.67]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8f7c7cd2becsm194526285a.29.2026.04.28.06.36.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Apr 2026 06:36:42 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1wHicD-0000000Aii6-3yTF; Tue, 28 Apr 2026 10:36:41 -0300 Date: Tue, 28 Apr 2026 10:36:41 -0300 From: Jason Gunthorpe To: fangyu.yu@linux.alibaba.com Cc: joro@8bytes.org, will@kernel.org, robin.murphy@arm.com, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, tjeznach@rivosinc.com, kevin.tian@intel.com, baolu.lu@linux.intel.com, vasant.hegde@amd.com, anup@brainfault.org, atish.patra@linux.dev, skhawaja@google.com, guoren@kernel.org, kvm@vger.kernel.org, iommu@lists.linux.dev, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 07/11] iommupt: Don't preset D when RISC-V IOMMU dirty tracking on Message-ID: <20260428133641.GF849557@ziepe.ca> References: <20260428131359.34872-1-fangyu.yu@linux.alibaba.com> <20260428131359.34872-8-fangyu.yu@linux.alibaba.com> Precedence: bulk X-Mailing-List: linux-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: <20260428131359.34872-8-fangyu.yu@linux.alibaba.com> On Tue, Apr 28, 2026 at 09:13:55PM +0800, fangyu.yu@linux.alibaba.com wrote: > From: Fangyu Yu > > When mapping writable pages, the RISC-V format code currently > pre-sets the PTE D bit unconditionally. > > If hardware dirty tracking is active (DC.tc.GADE set), the IOMMU > sets D autonomously on the first write. Pre-setting D makes every > new mapping appear dirty immediately and breaks dirty tracking. > > Introduce PT_FEAT_RISCV_DIRTY_TRACKING_ACTIVE and, when set, leave > D cleared for new writable mappings so hardware can capture the > first write. Keep pre-setting D when dirty tracking is inactive. > > Only meaningful for second-stage (iohgatp) page tables. You shouldn't need anything like this, the D bit is managed by the iommufd core appropriately. It *should* start out pre-set as that is faster when not tacking. Only once dirty tracking is started does D get cleared. User space is supposed to assume that everything is dirty prior to its first D clear. Jason