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[86.165.42.133]) by smtp.gmail.com with ESMTPSA id b9sm13731353wmd.32.2021.01.08.03.33.57 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 08 Jan 2021 03:33:58 -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: 104bf7db-5748-49e8-9b3c-4aeda9ebd49a 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=T5VnWk3JtgIl1kDrDNlFwgNbBbmI3MBD3aA0me1f7G8=; b=VxFD9XjT/nFpWlB71pwCYgqYDxRD5mz/rzUANHeYDqTwRSR7AnLmM7lfcJJ/mPTxkP NwEEDLoXcOVurr6kvHmDA6Y3UCUc3sJccbNEqayYR/1dGaMrxCqA3rE/bsUjboRatJIk 8/C5Ri8VZezTOIx3+VJZrpMYEldA2rquE18OrTibEOWGVba21aOVdcfq8vTc9ovB1HVv UzAUfHBMQ8O03cATTJH5apMxU/ezraixC3MB3ecG6lklGHioA2JY32ohDCHx2x3xc7SG +1JHzCCWRJptLIv0W1Xfi60XsNKxuEwJebLjk2fIj+UohNDrplQoMjj0az1x7AzmMCXS XZfA== 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=T5VnWk3JtgIl1kDrDNlFwgNbBbmI3MBD3aA0me1f7G8=; b=jnqSNF5p6wZ0FFtuiVgPg/ow1vUP7/TIqgXVeYTj26SxVFVQ1az7chy09by8ajjgGJ E0tIdsqTPDnyHYDfNK2dPm+nYH8L0H/45Xj5q7RjPEQ8/c9RBQttt/PnVeQHfRf3vCd7 cf2Yb/r0h0SR/21aCeH/s943Hj6R56J+6gIPvEtdBJXClpRTO4xMBXcxqI8v0VZFr5a2 MQikbpAU1/IxQY4aKRPjilXpkI63HOcog+YRgSgKBwixfxJ+IPZkyzjfUjgeyvuKytiJ sqRFuAkqI5miBAQ/3LTZoq274xalqoNYikGj5oSLa/dgUP7ncH4FUjacEJJK4gFv3Yq1 W02A== X-Gm-Message-State: AOAM530mbNHvx/MIjbGy1ge2yl3kFGsc/XwGx/eNTCCLoOhjs9drbcd4 IA/rlc0c/QUgCoBX3LVjvnU= X-Google-Smtp-Source: ABdhPJwPkGIoDY1b2ylqW8onMzNWaLOJXxgRq5yxxOd+NGY6MAJZGsjubmSC+jcwYcDc13Dyd3sOBw== X-Received: by 2002:adf:9467:: with SMTP id 94mr3298742wrq.235.1610105638775; Fri, 08 Jan 2021 03:33:58 -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> In-Reply-To: Subject: RE: [PATCH 2/2] viridian: allow vCPU hotplug for Windows VMs Date: Fri, 8 Jan 2021 11:33:57 -0000 Message-ID: <00a101d6e5b2$276b2140$764163c0$@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+9hzKltDykg > -----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 >=20 > 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). >=20 > 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. >=20 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? Paul > Igor