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[109.66.7.121]) by smtp.gmail.com with ESMTPSA id n6sm30959889wrs.81.2020.04.29.00.38.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Apr 2020 00:38:15 -0700 (PDT) Date: Wed, 29 Apr 2020 03:38:13 -0400 From: "Michael S. Tsirkin" To: Ani Sinha Subject: Re: [PATCH V2] Add a new PIIX option to control PCI hot unplugging of devices on non-root buses Message-ID: <20200429033657-mutt-send-email-mst@kernel.org> References: <20200428121837-mutt-send-email-mst@kernel.org> <20200428164428-mutt-send-email-mst@kernel.org> <20200429011228-mutt-send-email-mst@kernel.org> <544B4749-9A1C-44BB-BD89-C37A7E8D86F4@nutanix.com> <20200429025200-mutt-send-email-mst@kernel.org> <20200429025535-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=mst@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/04/29 01:18:10 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: Eduardo Habkost , "qemu-devel@nongnu.org" , Aleksandar Markovic , Paolo Bonzini , Ani Sinha , Igor Mammedov , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Aurelien Jarno , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Apr 29, 2020 at 07:02:56AM +0000, Ani Sinha wrote: >=20 >=20 > > On Apr 29, 2020, at 12:27 PM, Michael S. Tsirkin wrote= : > >=20 > > On Wed, Apr 29, 2020 at 06:54:52AM +0000, Ani Sinha wrote: > >>=20 > >>=20 > >>> On Apr 29, 2020, at 12:22 PM, Michael S. Tsirkin wro= te: > >>>=20 > >>> On Wed, Apr 29, 2020 at 06:11:20AM +0000, Ani Sinha wrote: > >>>>=20 > >>>>=20 > >>>>> On Apr 29, 2020, at 10:58 AM, Michael S. Tsirkin w= rote: > >>>>>=20 > >>>>> o if there's a need to disable > >>>>> just one of these, commit log needs to do a better job documenting = the > >>>>> usecase. > >>>>=20 > >>>> The use case is simple. With this feature admins will be able to do = what they were forced to do from Windows driver level but now at the bus le= vel. Hence,=20 > >>>> (a) They need not have access to the guest VM to change or update wi= ndows driver registry settings. They can enable the same setting from admin= management console without any access to VM. > >>>> (b) It is more robust. No need to mess with driver settings. Incorre= ct settings can brick guest OS. Also no guest specific knowhow required. > >>>> (c) It is more scalable since a single cluster wide setting can be u= sed for all VM power ons and the management plane can take care of the rest= automatically. No need to access individual VMs to enforce this. > >>>> (d) I am told that the driver level solution does not persist across= a reboot.=20 > >>>>=20 > >>>> Ani > >>>=20 > >>> Looks like disabling both plug and unplug would also address these ne= eds. > >>=20 > >> No the driver level solution does not prevent hot plugging of devices = but blocks just hot unplugging. The solution I am proposing tries to do the= same but from the bus/hypervisor level. > >=20 > > Why does the driver level solution need to prevent just hot unplugging? >=20 > Because it not fair to prevent end users from hot plugging new devices wh= en it is the (accidental?) hot unplugging of existing devices which causes = issues. Accidental? So maybe what you need is actually something else then - avoid *removing* the device when it's powered down. > >=20 > >=20 > >>=20 > >>> --=20 > >>> MST