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Tsirkin" To: Alex =?iso-8859-1?Q?Benn=E9e?= Subject: Re: [RFC PATCH] hw/virtio/vhost: re-factor vhost-section and allow DIRTY_MEMORY_CODE Message-ID: <20200604071504-mutt-send-email-mst@kernel.org> References: <20200604111323.7458-1-alex.bennee@linaro.org> MIME-Version: 1.0 In-Reply-To: <20200604111323.7458-1-alex.bennee@linaro.org> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=mst@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/04 01:31:23 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, Stefan Hajnoczi , "Dr . David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jun 04, 2020 at 12:13:23PM +0100, Alex Bennée wrote: > The purpose of vhost_section is to identify RAM regions that need to > be made available to a vhost client. However when running under TCG > all RAM sections have DIRTY_MEMORY_CODE set which leads to problems > down the line. The original comment implies VGA regions are a problem > but doesn't explain why vhost has a problem with it. > > Re-factor the code so: > > - steps are clearer to follow > - reason for rejection is recorded in the trace point > - we allow DIRTY_MEMORY_CODE when TCG is enabled > > Signed-off-by: Alex Bennée > Cc: Michael S. Tsirkin > Cc: Dr. David Alan Gilbert > Cc: Stefan Hajnoczi > --- > hw/virtio/vhost.c | 46 ++++++++++++++++++++++++++++++++-------------- > 1 file changed, 32 insertions(+), 14 deletions(-) > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > index aff98a0ede5..f81fc87e74c 100644 > --- a/hw/virtio/vhost.c > +++ b/hw/virtio/vhost.c > @@ -27,6 +27,7 @@ > #include "migration/blocker.h" > #include "migration/qemu-file-types.h" > #include "sysemu/dma.h" > +#include "sysemu/tcg.h" > #include "trace.h" > > /* enabled until disconnected backend stabilizes */ > @@ -403,26 +404,43 @@ static int vhost_verify_ring_mappings(struct vhost_dev *dev, > return r; > } > > +/* > + * vhost_section: identify sections needed for vhost access > + * > + * We only care about RAM sections here (where virtqueue can live). If > + * we find one we still allow the backend to potentially filter it out > + * of our list. > + */ > static bool vhost_section(struct vhost_dev *dev, MemoryRegionSection *section) > { > - bool result; > - bool log_dirty = memory_region_get_dirty_log_mask(section->mr) & > - ~(1 << DIRTY_MEMORY_MIGRATION); > - result = memory_region_is_ram(section->mr) && > - !memory_region_is_rom(section->mr); > - > - /* Vhost doesn't handle any block which is doing dirty-tracking other > - * than migration; this typically fires on VGA areas. > - */ > - result &= !log_dirty; > + enum { OK = 0, NOT_RAM, DIRTY, FILTERED } result = NOT_RAM; I'm not sure what does this enum buy us as compared to bool. Also why force OK to 0? And I prefer an explicit "else result = NOT_RAM" below instead of initializing it here. > + > + if (memory_region_is_ram(section->mr) && !memory_region_is_rom(section->mr)) { > + uint8_t dirty_mask = memory_region_get_dirty_log_mask(section->mr); > + uint8_t handled_dirty; > > - if (result && dev->vhost_ops->vhost_backend_mem_section_filter) { > - result &= > - dev->vhost_ops->vhost_backend_mem_section_filter(dev, section); > + /* > + * Vhost doesn't handle any block which is doing dirty-tracking other > + * than migration; this typically fires on VGA areas. However > + * for TCG we also do dirty code page tracking which shouldn't > + * get in the way. > + */ > + handled_dirty = (1 << DIRTY_MEMORY_MIGRATION); > + if (tcg_enabled()) { > + handled_dirty |= (1 << DIRTY_MEMORY_CODE); > + } So DIRTY_MEMORY_CODE is only set by TCG right? Thus I'm guessing we can just allow this unconditionally. > + if (dirty_mask & ~handled_dirty) { > + result = DIRTY; > + } else if (dev->vhost_ops->vhost_backend_mem_section_filter && > + !dev->vhost_ops->vhost_backend_mem_section_filter(dev, section)) { > + result = FILTERED; > + } else { > + result = OK; > + } > } > > trace_vhost_section(section->mr->name, result); > - return result; > + return result == OK; > } > > static void vhost_begin(MemoryListener *listener) > -- > 2.20.1