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Tsirkin" To: David Hildenbrand Cc: qemu-devel@nongnu.org, Stefan Hajnoczi , "Dr . David Alan Gilbert" , Tiwei Bie Subject: Re: [PATCH v1 1/2] vhost: Defer filtering memory sections until building the vhost memory structure Message-ID: <20230216070037-mutt-send-email-mst@kernel.org> References: <20230216114752.198627-1-david@redhat.com> <20230216114752.198627-2-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230216114752.198627-2-david@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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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=-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, Feb 16, 2023 at 12:47:51PM +0100, David Hildenbrand wrote: > Having multiple devices, some filtering memslots and some not filtering > memslots, messes up the "used_memslot" accounting. If we'd have a device > the filters out less memory sections after a device that filters out more, > we'd be in trouble, because our memslot checks stop working reliably. > For example, hotplugging a device that filters out less memslots might end > up passing the checks based on max vs. used memslots, but can run out of > memslots when getting notified about all memory sections. > > Further, it will be helpful in memory device context in the near future > to know that a RAM memory region section will consume a memslot, and be > accounted for in the used vs. free memslots, such that we can implement > reservation of memslots for memory devices properly. Whether a device > filters this out and would theoretically still have a free memslot is > then hidden internally, making overall vhost memslot accounting easier. > > Let's filter the memslots when creating the vhost memory array, > accounting all RAM && !ROM memory regions as "used_memslots" even if > vhost_user isn't interested in anonymous RAM regions, because it needs > an fd. > > When a device actually filters out regions (which should happen rarely > in practice), we might detect a layout change although only filtered > regions changed. We won't bother about optimizing that for now. That caused trouble in the past when using VGA because it is playing with mappings in weird ways. I think we have to optimize it, sorry. > Note: we cannot simply filter out the region and count them as > "filtered" to add them to used, because filtered regions could get > merged and result in a smaller effective number of memslots. Further, > we won't touch the hmp/qmp virtio introspection output. > > Fixes: 988a27754bbb ("vhost: allow backends to filter memory sections") > Cc: Tiwei Bie > Signed-off-by: David Hildenbrand I didn't review this yet but maybe you can answer: will this create more slots for the backend? Because some backends are limited in # of slots and breaking them is not a good idea. Thanks! > --- > hw/virtio/vhost.c | 79 +++++++++++++++++++++++++++++++++-------------- > 1 file changed, 55 insertions(+), 24 deletions(-) > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > index eb8c4c378c..b7fb960fa9 100644 > --- a/hw/virtio/vhost.c > +++ b/hw/virtio/vhost.c > @@ -219,8 +219,13 @@ static void vhost_log_sync_range(struct vhost_dev *dev, > int i; > /* FIXME: this is N^2 in number of sections */ > for (i = 0; i < dev->n_mem_sections; ++i) { > - MemoryRegionSection *section = &dev->mem_sections[i]; > - vhost_sync_dirty_bitmap(dev, section, first, last); > + MemoryRegionSection *mrs = &dev->mem_sections[i]; > + > + if (dev->vhost_ops->vhost_backend_mem_section_filter && > + !dev->vhost_ops->vhost_backend_mem_section_filter(dev, mrs)) { > + continue; > + } > + vhost_sync_dirty_bitmap(dev, mrs, first, last); > } > } > > @@ -503,12 +508,6 @@ static bool vhost_section(struct vhost_dev *dev, MemoryRegionSection *section) > return false; > } > > - if (dev->vhost_ops->vhost_backend_mem_section_filter && > - !dev->vhost_ops->vhost_backend_mem_section_filter(dev, section)) { > - trace_vhost_reject_section(mr->name, 2); > - return false; > - } > - > trace_vhost_section(mr->name); > return true; > } else { > @@ -525,6 +524,43 @@ static void vhost_begin(MemoryListener *listener) > dev->n_tmp_sections = 0; > } > > +static void vhost_realloc_vhost_memory(struct vhost_dev *dev, > + unsigned int nregions) > +{ > + const size_t size = offsetof(struct vhost_memory, regions) + > + nregions * sizeof dev->mem->regions[0]; > + > + dev->mem = g_realloc(dev->mem, size); > + dev->mem->nregions = nregions; > +} > + > +static void vhost_rebuild_vhost_memory(struct vhost_dev *dev) > +{ > + unsigned int nregions = 0; > + int i; > + > + vhost_realloc_vhost_memory(dev, dev->n_mem_sections); > + for (i = 0; i < dev->n_mem_sections; i++) { > + struct MemoryRegionSection *mrs = dev->mem_sections + i; > + struct vhost_memory_region *cur_vmr; > + > + if (dev->vhost_ops->vhost_backend_mem_section_filter && > + !dev->vhost_ops->vhost_backend_mem_section_filter(dev, mrs)) { > + continue; > + } > + cur_vmr = dev->mem->regions + nregions; > + nregions++; > + > + cur_vmr->guest_phys_addr = mrs->offset_within_address_space; > + cur_vmr->memory_size = int128_get64(mrs->size); > + cur_vmr->userspace_addr = > + (uintptr_t)memory_region_get_ram_ptr(mrs->mr) + > + mrs->offset_within_region; > + cur_vmr->flags_padding = 0; > + } > + vhost_realloc_vhost_memory(dev, nregions); > +} > + > static void vhost_commit(MemoryListener *listener) > { > struct vhost_dev *dev = container_of(listener, struct vhost_dev, > @@ -532,7 +568,6 @@ static void vhost_commit(MemoryListener *listener) > MemoryRegionSection *old_sections; > int n_old_sections; > uint64_t log_size; > - size_t regions_size; > int r; > int i; > bool changed = false; > @@ -564,23 +599,19 @@ static void vhost_commit(MemoryListener *listener) > goto out; > } > > - /* Rebuild the regions list from the new sections list */ > - regions_size = offsetof(struct vhost_memory, regions) + > - dev->n_mem_sections * sizeof dev->mem->regions[0]; > - dev->mem = g_realloc(dev->mem, regions_size); > - dev->mem->nregions = dev->n_mem_sections; > + /* > + * Globally track the used memslots *without* device specific > + * filtering. This way, we always know how many memslots are required > + * when devices with differing filtering requirements get mixed, and > + * all RAM memory regions of memory devices will consume memslots. > + */ > used_memslots = dev->mem->nregions; > - for (i = 0; i < dev->n_mem_sections; i++) { > - struct vhost_memory_region *cur_vmr = dev->mem->regions + i; > - struct MemoryRegionSection *mrs = dev->mem_sections + i; > > - cur_vmr->guest_phys_addr = mrs->offset_within_address_space; > - cur_vmr->memory_size = int128_get64(mrs->size); > - cur_vmr->userspace_addr = > - (uintptr_t)memory_region_get_ram_ptr(mrs->mr) + > - mrs->offset_within_region; > - cur_vmr->flags_padding = 0; > - } > + /* > + * Rebuild the regions list from the new sections list, filtering out all > + * sections that this device is not interested in. > + */ > + vhost_rebuild_vhost_memory(dev); > > if (!dev->started) { > goto out; > -- > 2.39.1