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Wed, 1 Apr 2020 17:40:03 +0000 From: Nadav Amit To: Wanpeng Li CC: Paolo Bonzini , LKML , kvm , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel Subject: Re: [PATCH v2 2/2] KVM: LAPIC: Don't need to clear IPI delivery status in x2apic mode Thread-Topic: [PATCH v2 2/2] KVM: LAPIC: Don't need to clear IPI delivery status in x2apic mode Thread-Index: AQHWB/FWdzgWY4YnU0q2HQ5H9CdmBahkiUOA Date: Wed, 1 Apr 2020 17:40:03 +0000 Message-ID: References: <1585700362-11892-1-git-send-email-wanpengli@tencent.com> <1585700362-11892-2-git-send-email-wanpengli@tencent.com> <6de1a454-60fc-2bda-841d-f9ceb606d4c6@redhat.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: spf=none (sender IP is ) smtp.mailfrom=namit@vmware.com; x-originating-ip: [2601:647:4700:9b2:4568:145a:b450:27e3] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: e7dcce41-d5e0-4363-5d60-08d7d663b5f6 x-ms-traffictypediagnostic: BYAPR05MB4997: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:8882; 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charset="us-ascii" Content-ID: <9F187A50EFA04A4B8361CED49AD3EAD8@namprd05.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: vmware.com X-MS-Exchange-CrossTenant-Network-Message-Id: e7dcce41-d5e0-4363-5d60-08d7d663b5f6 X-MS-Exchange-CrossTenant-originalarrivaltime: 01 Apr 2020 17:40:03.7953 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b39138ca-3cee-4b4a-a4d6-cd83d9dd62f0 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: aNIyci8QvJj1KaMJpM+0AARB5myi0o2U1v6s1gYpFH8YV3o5q2Hc6SFJajNdvEEmfPqcx+qJ/RlaJputQla/gg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR05MB4997 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Mar 31, 2020, at 11:46 PM, Wanpeng Li wrote: >=20 > Cc more people, > On Wed, 1 Apr 2020 at 08:35, Paolo Bonzini wrote: >> On 01/04/20 02:19, Wanpeng Li wrote: >>> - /* No delay here, so we always clear the pending bit */ >>> - val &=3D ~(1 << 12); >>> + /* Immediately clear Delivery Status in xAPIC mode */ >>> + if (!apic_x2apic_mode(apic)) >>> + val &=3D ~(1 << 12); >>=20 >> This adds a conditional, and the old behavior was valid according to the >> SDM: "software should not assume the value returned by reading the ICR >> is the last written value". >=20 > Nadav, Sean, what do you think? I do not know. But if you write a KVM unit-test, I can run it on bare-metal and give you feedback about how it behaves.