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Tsirkin" To: "Duan, Zhenzhong" Cc: Jason Wang , "qemu-devel@nongnu.org" , "Peng, Chao P" , "Liu, Yi L" , =?iso-8859-1?Q?Cl=E9ment?= Mathieu--Drif , Paolo Bonzini , Richard Henderson , Eduardo Habkost , Marcel Apfelbaum Subject: Re: [PATCH v2] intel_iommu: Introduce property "x-stale-tm" to control Transient Mapping (TM) field Message-ID: <20241019202416-mutt-send-email-mst@kernel.org> References: <20241010075354.3582221-1-zhenzhong.duan@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1.25, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, Oct 17, 2024 at 07:57:53AM +0000, Duan, Zhenzhong wrote: > > > >-----Original Message----- > >From: Jason Wang > >Subject: Re: [PATCH v2] intel_iommu: Introduce property "x-stale-tm" to control > >Transient Mapping (TM) field > > > >On Thu, Oct 10, 2024 at 3:57 PM Zhenzhong Duan > >wrote: > >> > >> VT-d spec removed Transient Mapping (TM) field from second-level page-tables > >> and treat the field as Reserved(0) since revision 3.2. > >> > >> Changing the field as reserved(0) will break backward compatibility, so > >> introduce a property "x-stale-tm" to allow user to control the setting. > > > >Nit: I think we probably don't need the x prefix? As we try to > >maintain the compatibility via: > > > >> + { TYPE_INTEL_IOMMU_DEVICE, "x-stale-tm", "on" }, > > > >? > > I'm fine to remove it. But, > The prefix "x-" is used to indicate that a feature is experimental. No, it is used to indicate that the feature is not part of a stable API. > Couldn't we have a property both experimental and compatible? > I see a lot of such properties: > > # grep "x-" /sdb/qemu/hw/i386/pc.c > { "ICH9-LPC", "x-smi-swsmi-timer", "off" }, > { "ICH9-LPC", "x-smi-periodic-timer", "off" }, > { TYPE_INTEL_IOMMU_DEVICE, "x-stale-tm", "on" }, > { TYPE_X86_CPU, "x-amd-topoext-features-only", "false" }, > { TYPE_X86_CPU, "x-l1-cache-per-thread", "false" }, > { "ICH9-LPC", "x-keep-pci-slot-hpc", "false" }, > { TYPE_X86_CPU, "x-vendor-cpuid-only", "off" }, > { "ICH9-LPC", "x-keep-pci-slot-hpc", "true" }, > { "ICH9-LPC", "x-smi-cpu-hotunplug", "off" }, > { "ICH9-LPC", "x-smi-cpu-hotplug", "off" }, > { TYPE_X86_CPU, "x-intel-pt-auto-level", "off" }, > { TYPE_X86_CPU, "x-hv-synic-kvm-only", "on" }, > { TYPE_X86_CPU, "x-migrate-smi-count", "off" }, > { TYPE_X86_CPU, "x-hv-max-vps", "0x40" }, > { "i440FX-pcihost", "x-pci-hole64-fix", "off" }, > { "q35-pcihost", "x-pci-hole64-fix", "off" }, > { "kvmclock", "x-mach-use-reliable-get-clock", "off" }, > { "ICH9-LPC", "x-smi-broadcast", "off" }, > > Thanks > Zhenzhong