From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 95973CD13D2 for ; Mon, 18 Sep 2023 11:50:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240421AbjIRLtz (ORCPT ); Mon, 18 Sep 2023 07:49:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47636 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241769AbjIRLtv (ORCPT ); Mon, 18 Sep 2023 07:49:51 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 94EA5E3; Mon, 18 Sep 2023 04:49:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=+Zla40yBeTjqO403RnbEECOA9lbJYqdXZE9AJUrnj7o=; b=E5Favm2RX6bIdAAyvY5mnOC94f /lLpilx1IR1CeLuPXaj9UyA2MUPtkPyfCZuRLSg70Trits2uAfmNJJVbVcrNxtUgwXHSmab23eUbX fhlNuwPK+TZKgOxjf3ANzUDTLLMlee2zHVYZ3QwbyWudB7yPKDV0s2exhRSywojM1xy5VuuyAOtnz claZx1R1Ydc/nVALP7mK7+yUp2GPGSVDTxAw7pNJAVjRYGCnbrHJ/co4nrijgFkd+foMcMIOQ/kMW z6+hb6PRq4sFTdGJ5a2WufWGmtp4s95FwH9amsfpCT7+jygGnC7rzUxxKnrujnwCOd1Gs8EWn345N YfE6WiMw==; Received: from [2001:8b0:10b:5:cea0:d147:7c2e:9e61] (helo=u3832b3a9db3152.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1qiCl5-00AorF-5E; Mon, 18 Sep 2023 11:49:43 +0000 Message-ID: <51027eb7552cac992f4c856ea2344f7d35c0185d.camel@infradead.org> Subject: Re: [PATCH v2 08/12] KVM: xen: automatically use the vcpu_info embedded in shared_info From: David Woodhouse To: Paul Durrant , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Paul Durrant , Sean Christopherson , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , x86@kernel.org Date: Mon, 18 Sep 2023 12:49:42 +0100 In-Reply-To: <20230918112148.28855-9-paul@xen.org> References: <20230918112148.28855-1-paul@xen.org> <20230918112148.28855-9-paul@xen.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-NvTxCzm21jgrjqvdo3RP" User-Agent: Evolution 3.44.4-0ubuntu2 MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-NvTxCzm21jgrjqvdo3RP Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2023-09-18 at 11:21 +0000, Paul Durrant wrote: > - This is because KVM may > -=C2=A0 not be aware of the Xen CPU id which is used as the index into th= e > -=C2=A0 vcpu_info[] array, so may know the correct default location. Hm, that *was* true at the time of writing, but we did end up teaching KVM about the Xen vcpu_id so that we can handle timers. (We required userspace to provide the APIC ID for all the other event channel stuff, but timer hypercalls come straight from the guest). But I think the *only* thing we use vcpu->arch.xen.vcpu_id for right now is acceleration of the timer hypercalls that are restricted to the vCPU that they're called from, e.g.: case VCPUOP_set_singleshot_timer: if (vcpu->arch.xen.vcpu_id !=3D vcpu_id) { *r =3D -EINVAL; So it's never mattered much before now if the Xen vcpu_id changes at runtime. Maybe you now want to invalidate the vcpu_info pfncache for a vCPU if its Xen vcpu_id changes? Or just *forbid* such a change after the shinfo page has been set up? 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