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Tsirkin" Subject: Re: [PATCH] virtio: skip guest index check on device load Message-ID: <20201028110038.GE221115@stefanha-x1.localdomain> References: <20201026151328.77611-1-felipe@nutanix.com> <20201027113049.GH79063@stefanha-x1.localdomain> <20201027082337-mutt-send-email-mst@kernel.org> <12146644-5D22-4CAC-9B4F-F16E84ED56AE@nutanix.com> <20201027085447-mutt-send-email-mst@kernel.org> <20201027090420-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: <20201027090420-mutt-send-email-mst@kernel.org> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="T6xhMxlHU34Bk0ad" Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/28 01:50:00 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_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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Jason Wang , "qemu-devel@nongnu.org" , Markus Armbruster , Felipe Franciosi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --T6xhMxlHU34Bk0ad Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Oct 27, 2020 at 09:04:46AM -0400, Michael S. Tsirkin wrote: > It's not a waste of time, it's just a lot of work > within guests. Luckily it does no harm to set the NEEDS_RESET bit even if the guest doesn't handle it. If the guest driver is unaware it may continue to submit requests to the device for a while. The device emulation code stops accepting new requests though. This means the device will become unresponsive until reset, which is not ideal but okay in the case where the device was put into an invalid state. I agree that supporting NEEDS_RESET transparently inside guests is difficult. The driver needs to reset and resume the device without reporting errors to applications. In some cases drivers may not have enough state in order to do that. It's also tricky to test all code paths. I guess this is why no one has done it: drivers shouldn't enter the NEEDS_RESET state anyway and handling it is complex. Stefan --T6xhMxlHU34Bk0ad Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAl+ZT1YACgkQnKSrs4Gr c8gbEQgAmoJQySu64D/fTL5kZD2xLV7vb6nBQoD8jVlprtIF6747LQn82me/93dK JcgR3TaWHDQI4HPxQQjyNYxhsnAiCxnqJCLJUoHXUS1nWgMr2uKHg6AcyoiS/52k FryIYtd54dmMTshNga7JeGI4UGLKPJMStki3o9s5F0IG/VNUlVE5HitDkGQQ02hD NSsCNktKj5NN5HyhB5KmGRRSMbhWkQa0UyGj41ToYoSip2ioy4B5gyzfYvDNscAI 4n4e1UZXp478JgmzsKlZWh8yUhgXOphT9PdghUz72vkF03hW6LOTcaMGIs1NT06i yy9uphiM+213Zk0Bw/sPs7QDo5ijIg== =MDNJ -----END PGP SIGNATURE----- --T6xhMxlHU34Bk0ad--