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Tsirkin" To: Eric Auger Cc: eric.auger.pro@gmail.com, qemu-devel@nongnu.org, qemu-arm@nongnu.org, jean-philippe@linaro.org, alex.williamson@redhat.com, clg@redhat.com, peter.maydell@linaro.org, Peter Xu Subject: Re: [PATCH v2] virtio-iommu: Use qemu_real_host_page_mask as default page_size_mask Message-ID: <20240213064017-mutt-send-email-mst@kernel.org> References: <20240117132039.332273-1-eric.auger@redhat.com> <20240213044312-mutt-send-email-mst@kernel.org> <6d4b5766-f8e2-4889-827d-01d3509239f7@redhat.com> <20240213060731-mutt-send-email-mst@kernel.org> <417ea71e-fb45-4e1d-b8e5-9d54d93dba3b@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <417ea71e-fb45-4e1d-b8e5-9d54d93dba3b@redhat.com> 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: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.504, 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=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 Tue, Feb 13, 2024 at 12:24:22PM +0100, Eric Auger wrote: > Hi Michael, > On 2/13/24 12:09, Michael S. Tsirkin wrote: > > On Tue, Feb 13, 2024 at 11:32:13AM +0100, Eric Auger wrote: > >> Do you have an other concern? > > I also worry a bit about migrating between hosts with different > > page sizes. Not with kvm I am guessing but with tcg it does work I think? > I have never tried but is it a valid use case? Adding Peter in CC. > > Is this just for vfio and vdpa? Can we limit this to these setups > > maybe? > I am afraid we know the actual use case too later. If the VFIO device is > hotplugged we have started working with 4kB granule. > > The other way is to introduce a min_granule option as done for aw-bits. > But it is heavier. > > Thanks > > Eric > > Let's say, if you are changing the default then we definitely want a way to get the cmpatible behaviour for tcg. So the compat machinery should be user-accessible too and documented. -- MST