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[159.2.73.22]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8ac84c464a4sm24186486d6.28.2026.04.10.07.13.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Apr 2026 07:13:56 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1wBCcN-0000000EKCb-2LBT; Fri, 10 Apr 2026 11:13:55 -0300 Date: Fri, 10 Apr 2026 11:13:55 -0300 From: Jason Gunthorpe To: Samiullah Khawaja Cc: Pranjal Shrivastava , Ankit Soni , David Woodhouse , Lu Baolu , Joerg Roedel , Will Deacon , Robin Murphy , Kevin Tian , Alex Williamson , Shuah Khan , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Saeed Mahameed , Adithya Jayachandran , Parav Pandit , Leon Romanovsky , William Tu , Pratyush Yadav , Pasha Tatashin , David Matlack , Andrew Morton , Chris Li , Vipin Sharma , YiFei Zhu Subject: Re: [PATCH 04/14] iommu/pages: Add APIs to preserve/unpreserve/restore iommu pages Message-ID: <20260410141355.GU2551565@ziepe.ca> References: <20260203220948.2176157-1-skhawaja@google.com> <20260203220948.2176157-5-skhawaja@google.com> Precedence: bulk X-Mailing-List: kvm@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: On Fri, Mar 20, 2026 at 06:12:28PM +0000, Samiullah Khawaja wrote: > > > > > +void iommu_restore_page(u64 phys) > > > > > +{ > > > > > + struct ioptdesc *iopt; > > > > > + struct folio *folio; > > > > > + unsigned long pgcnt; > > > > > + unsigned int order; > > > > > + > > > > > + folio = kho_restore_folio(phys); > > > > > + BUG_ON(!folio); > > > > > + > > > > > + iopt = folio_ioptdesc(folio); > > > > > > > > iopt->incoherent = false; should be here? > > > > > > > > > > Yes this should be set here. I will update this. > > > > I'm wondering if we are silently losing state here. What if the > > preserved page was actually incoherent in the previous kernel? > > I understand we likely need to initialize it to false here because we > > don't have a dev pointer for DMA sync operations at this low level (though > > x86 uses clflush). > > > > But when is it set back to "incoherent" again? I don't see that > > happening during the driver re-attach phase? > > This can be done during restore_domain as the domain has a reference to > the dev when it is recreated. I will updated the walker and add this in > the next revision. The only reason for this tracking is for DMA API debugging. It might be better to just remove the DMA API from this path and use a direct cache flush. Then you don't really need to care, the successor kernel never writes to this memory so it can just free it in a normal way. Otherwise you have to remap it on restore so you can unmap it on free. Jason