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[86.165.42.133]) by smtp.gmail.com with ESMTPSA id k10sm12367935wrq.38.2021.01.08.03.40.42 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 08 Jan 2021 03:40:43 -0800 (PST) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 08cc096b-710d-425d-83ff-abb1abbdc81c DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:reply-to:to:cc:references:in-reply-to:subject:date:message-id :mime-version:content-transfer-encoding:content-language :thread-index; bh=wx4rRMTQv/GFUHNtO2xLlGDua22QKTl/lDSIyor++LA=; b=aWlGx2B06yejb4y0oE+weA7cYlEIZyr53gpumDyr2yl839ukNiVbtCSeQHyMey/z1y rOkpEkYK8bSXIXr8r4f5ZgX57Xd7mmXaNrEE9P3ydT8jFiqgsnTNtExSZOtuG5M1yL9O HSPnO8Fj5SAQKJRzfj9UrY809rL6jod5Bxm34FEOeJNr/V/KIsXiTtG8TouF3Alo6Y1G uBhx+lopgWs3tIvs3k9UE86Bu/Vak5l5xQvvfyvt6Yh2JgSsb7+MhzmreBVWBnNkqhGu MQsHPfci2YmjwqC/5HjdvFKYvbVrQOUf0jUXEoPfqMBYSvrpGDY5Cg8eZNa6NppnqmFB bU6w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:reply-to:to:cc:references:in-reply-to :subject:date:message-id:mime-version:content-transfer-encoding :content-language:thread-index; bh=wx4rRMTQv/GFUHNtO2xLlGDua22QKTl/lDSIyor++LA=; b=Q04lwVxYrd2lxHZapbYspCaU8g2dXJbZ/fvA/iK7XMn1hue1xao6Dqbz0W/nwARBqr bP9ebuUAd4RSOkYbb6R0UXtj6V+VveWDhgdW80TsQrHJfpuRc5kDSt7SIsDGxOhOICIC SWhDCUmzFIJluZ/rNjOpHJ72wwc5u5906FzYvKCetU5IIEy5GPwWkD8rv6GnY4xx0Dam bXZxljczIAYbeDY2yADP9xHXrbY/Im4ZkV4AD/v+YMKy6IOxVSHZXqlA18Vo9WMRG5fb bAdWPdao2YcrwLKUS/r3lhjZ4nTVAxG2P377ErjClTcQxVIVLsCiTohVPVfLG4E1VPay vGvw== X-Gm-Message-State: AOAM530ye44kcCIQIU9QsNxNa7xhaDfq7EE0HAyZ5RdXSgZ+C7G7SqlN E6gf6EB3HjTdIJDGR6abPuQ= X-Google-Smtp-Source: ABdhPJx55vjcOdSo46YBOQ/P4ScnU9jzo71i0UtpVtocs/VMQHcgvb6zNYpqQEM/tMezUuKfs3xcGA== X-Received: by 2002:adf:80ae:: with SMTP id 43mr3290425wrl.50.1610106043508; Fri, 08 Jan 2021 03:40:43 -0800 (PST) From: Paul Durrant X-Google-Original-From: "Paul Durrant" Reply-To: To: "'Igor Druzhinin'" , Cc: , , , , , , , , References: <1610066796-17266-1-git-send-email-igor.druzhinin@citrix.com> <1610066796-17266-2-git-send-email-igor.druzhinin@citrix.com> <00a001d6e599$a07c8380$e1758a80$@xen.org> <00a101d6e5b2$276b2140$764163c0$@xen.org> In-Reply-To: Subject: RE: [PATCH 2/2] viridian: allow vCPU hotplug for Windows VMs Date: Fri, 8 Jan 2021 11:40:42 -0000 Message-ID: <00a201d6e5b3$18ad0ff0$4a072fd0$@xen.org> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Mailer: Microsoft Outlook 16.0 Content-Language: en-gb Thread-Index: AQIZObzvX1fStk6d0If1Grmzp4ChNQGw5HmOAetIvREB3+9hzAIndkP3AVj957ypUQ1UYA== > -----Original Message----- > From: Igor Druzhinin > Sent: 08 January 2021 11:36 > To: paul@xen.org; xen-devel@lists.xenproject.org > Cc: wl@xen.org; iwj@xenproject.org; anthony.perard@citrix.com; = andrew.cooper3@citrix.com; > george.dunlap@citrix.com; jbeulich@suse.com; julien@xen.org; = sstabellini@kernel.org; > roger.pau@citrix.com > Subject: Re: [PATCH 2/2] viridian: allow vCPU hotplug for Windows VMs >=20 > On 08/01/2021 11:33, Paul Durrant wrote: > >> -----Original Message----- > >> From: Igor Druzhinin > >> Sent: 08 January 2021 11:30 > >> To: paul@xen.org; xen-devel@lists.xenproject.org > >> Cc: wl@xen.org; iwj@xenproject.org; anthony.perard@citrix.com; = andrew.cooper3@citrix.com; > >> george.dunlap@citrix.com; jbeulich@suse.com; julien@xen.org; = sstabellini@kernel.org; > >> roger.pau@citrix.com > >> Subject: Re: [PATCH 2/2] viridian: allow vCPU hotplug for Windows = VMs > >> > >> On 08/01/2021 08:38, Paul Durrant wrote: > >>>> -----Original Message----- > >>>> From: Igor Druzhinin > >>>> Sent: 08 January 2021 00:47 > >>>> To: xen-devel@lists.xenproject.org > >>>> Cc: paul@xen.org; wl@xen.org; iwj@xenproject.org; = anthony.perard@citrix.com; > >>>> andrew.cooper3@citrix.com; george.dunlap@citrix.com; = jbeulich@suse.com; julien@xen.org; > >>>> sstabellini@kernel.org; roger.pau@citrix.com; Igor Druzhinin = > >>>> Subject: [PATCH 2/2] viridian: allow vCPU hotplug for Windows VMs > >>>> > >>>> If Viridian extensions are enabled, Windows wouldn't currently = allow > >>>> a hotplugged vCPU to be brought up dynamically. We need to expose = a special > >>>> bit to let the guest know we allow it. It appears we can just = start exposing > >>>> it without worrying too much about compatibility - see relevant = QEMU > >>>> discussion here: > >>>> > >>>> = https://patchwork.kernel.org/project/qemu-devel/patch/1455364815-19586-1-= git-send-email- > >>>> den@openvz.org/ > >>> > >>> I don't think that discussion really confirmed it was safe... just = that empirically it appeared to > >> be so. I think we should err on > >>> the side of caution and have this behind a feature flag (but I'm = happy for it to default to on). > >> > >> QEMU was having this code since 2016 and nobody complained is good > >> enough for me - but if you insist we need an option - ok, I will = add one. > >> > > > > Given that it has not yet been in a release, perhaps you could just = guard this and the > implementation of leaf 0x40000005 using HVMPV_ex_processor_masks? >=20 > That looks sloppy and confusing to me - let's have a separate option = instead. >=20 Yes, for this I guess it is really a separate thing. Using = HVMPV_ex_processor_masks to control the presence of leaf 0x40000005 = seems reasonable (since it's all about being able to use >64 vcpus). = Perhaps a new HVMPV_cpu_hotplug for this one? Paul > Igor