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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 Subject: Re: [PATCH v2] virtio-iommu: Use qemu_real_host_page_mask as default page_size_mask Message-ID: <20240213060544-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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6d4b5766-f8e2-4889-827d-01d3509239f7@redhat.com> Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.774, 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_H4=0.001, RCVD_IN_MSPIKE_WL=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 11:32:13AM +0100, Eric Auger wrote: > Hi Michael, > > On 2/13/24 10:43, Michael S. Tsirkin wrote: > > On Wed, Jan 17, 2024 at 02:20:39PM +0100, Eric Auger wrote: > >> We used to set default page_size_mask to qemu_target_page_mask() but > >> with VFIO assignment it makes more sense to use the actual host page mask > >> instead. > >> > >> So from now on qemu_real_host_page_mask() will be used as a default. > >> To be able to migrate older code, we increase the vmstat version_id > >> to 3 and if an older incoming v2 stream is detected we set the previous > >> default value. > >> > >> The new default is well adapted to configs where host and guest have > >> the same page size. This allows to fix hotplugging VFIO devices on a > >> 64kB guest and a 64kB host. This test case has been failing before > >> and even crashing qemu with hw_error("vfio: DMA mapping failed, > >> unable to continue") in VFIO common). Indeed the hot-attached VFIO > >> device would call memory_region_iommu_set_page_size_mask with 64kB > >> mask whereas after the granule was frozen to 4kB on machine init done. > >> Now this works. However the new default will prevent 4kB guest on > >> 64kB host because the granule will be set to 64kB which would be > >> larger than the guest page size. In that situation, the virtio-iommu > >> driver fails on viommu_domain_finalise() with > >> "granule 0x10000 larger than system page size 0x1000". > >> > >> The current limitation of global granule in the virtio-iommu > >> should be removed and turned into per domain granule. But > >> until we get this upgraded, this new default is probably > >> better because I don't think anyone is currently interested in > >> running a 4kB page size guest with virtio-iommu on a 64kB host. > >> However supporting 64kB guest on 64kB host with virtio-iommu and > >> VFIO looks a more important feature. > >> > >> Signed-off-by: Eric Auger > >> Tested-by: Jean-Philippe Brucker > >> Reviewed-by: Jean-Philippe Brucker > > What about migration compatibility? In particular, cross-version one? > > Don't we need compat machinery for this? > See below > > > >> --- > >> > >> v1 -> v2: > >> - fixed 2 typos in the commit msg and added Jean's R-b and T-b > >> --- > >> hw/virtio/virtio-iommu.c | 7 +++++-- > >> 1 file changed, 5 insertions(+), 2 deletions(-) > >> > >> diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c > >> index 8a4bd933c6..ec2ba11d1d 100644 > >> --- a/hw/virtio/virtio-iommu.c > >> +++ b/hw/virtio/virtio-iommu.c > >> @@ -1313,7 +1313,7 @@ static void virtio_iommu_device_realize(DeviceState *dev, Error **errp) > >> * in vfio realize > >> */ > >> s->config.bypass = s->boot_bypass; > >> - s->config.page_size_mask = qemu_target_page_mask(); > >> + s->config.page_size_mask = qemu_real_host_page_mask(); > >> s->config.input_range.end = UINT64_MAX; > >> s->config.domain_range.end = UINT32_MAX; > >> s->config.probe_size = VIOMMU_PROBE_SIZE; > >> @@ -1491,13 +1491,16 @@ static int iommu_post_load(void *opaque, int version_id) > >> * still correct. > >> */ > >> virtio_iommu_switch_address_space_all(s); > >> + if (version_id <= 2) { > >> + s->config.page_size_mask = qemu_target_page_mask(); > I tested migration from v2 -> v3 and the above code is overriding the > new default by the older one. > > Do you have an other concern? > > Thanks > > Eric > >> + } > >> return 0; > >> } > >> > >> static const VMStateDescription vmstate_virtio_iommu_device = { > >> .name = "virtio-iommu-device", > >> .minimum_version_id = 2, > >> - .version_id = 2, > >> + .version_id = 3, > >> .post_load = iommu_post_load, > >> .fields = (const VMStateField[]) { > >> VMSTATE_GTREE_DIRECT_KEY_V(domains, VirtIOIOMMU, 2, Oh I missed the version change. But then migration to older version is completely broken isn't it? Old qemu can not handle version_id 3 at all. Generally, compat machinery is nicer than the old version hacks. > >> -- > >> 2.41.0