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Tsirkin" Subject: Re: [PATCH V2] Add a new PIIX option to control PCI hot unplugging of devices on non-root buses Thread-Topic: [PATCH V2] Add a new PIIX option to control PCI hot unplugging of devices on non-root buses Thread-Index: AQHWHUYvMyDNYIpa20C9378Nh0w8t6iOszWAgAAA+QCAAANNgIAABV8AgABEbYCAAEbYAIAASz+AgAAMEQCAAAuhAIAAAIgAgAAAq4CAAAGWAA== Date: Wed, 29 Apr 2020 07:02:56 +0000 Message-ID: References: <20200428120426-mutt-send-email-mst@kernel.org> <67e481a5-de04-4e01-b9ec-70932194d69f@Spark> <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> In-Reply-To: <20200429025535-mutt-send-email-mst@kernel.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: redhat.com; dkim=none (message not signed) header.d=none;redhat.com; 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charset="iso-8859-1" Content-ID: <99414B97D1967841B3370C88C95E0903@namprd02.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: nutanix.com X-MS-Exchange-CrossTenant-Network-Message-Id: 8bd5fc06-d8c2-4ee5-a962-08d7ec0b5883 X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Apr 2020 07:02:56.8954 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: bb047546-786f-4de1-bd75-24e5b6f79043 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: hYuOu2bHE3IH+2kX/rh+njzdMqZyXw6G4+hmJbe85UpD7mX9kHYjJY7ofC6oMrNEdN0HgDLbxoKC5f5fIh6dHg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR02MB5967 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.676 definitions=2020-04-29_02:2020-04-28, 2020-04-29 signatures=0 X-Proofpoint-Spam-Reason: safe Received-SPF: pass client-ip=148.163.155.12; envelope-from=ani.sinha@nutanix.com; helo=mx0b-002c1b01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/04/29 02:11:36 X-ACL-Warn: Detected OS = Linux 3.x [generic] X-Received-From: 148.163.155.12 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 , =?iso-8859-1?Q?Philippe_Mathieu-Daud=E9?= , Aurelien Jarno , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" > 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 wrote= : >>>=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 wro= te: >>>>>=20 >>>>> o if there's a need to disable >>>>> just one of these, commit log needs to do a better job documenting th= e >>>>> usecase. >>>>=20 >>>> The use case is simple. With this feature admins will be able to do wh= at they were forced to do from Windows driver level but now at the bus leve= l. Hence,=20 >>>> (a) They need not have access to the guest VM to change or update wind= ows driver registry settings. They can enable the same setting from admin m= anagement console without any access to VM. >>>> (b) It is more robust. No need to mess with driver settings. Incorrect= settings can brick guest OS. Also no guest specific knowhow required. >>>> (c) It is more scalable since a single cluster wide setting can be use= d for all VM power ons and the management plane can take care of the rest a= utomatically. 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 need= s. >>=20 >> No the driver level solution does not prevent hot plugging of devices bu= t blocks just hot unplugging. The solution I am proposing tries to do the s= ame but from the bus/hypervisor level. >=20 > Why does the driver level solution need to prevent just hot unplugging? Because it not fair to prevent end users from hot plugging new devices when= it is the (accidental?) hot unplugging of existing devices which causes is= sues. =20 >=20 >=20 >>=20 >>> --=20 >>> MST