From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 52752CA4A for ; Thu, 16 Nov 2023 14:25:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from lhrpeml500003.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4SWMC54dvMz6GDCc; Thu, 16 Nov 2023 22:01:21 +0800 (CST) Received: from lhrpeml500001.china.huawei.com (7.191.163.213) by lhrpeml500003.china.huawei.com (7.191.162.67) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.31; Thu, 16 Nov 2023 14:06:03 +0000 Received: from lhrpeml500001.china.huawei.com ([7.191.163.213]) by lhrpeml500001.china.huawei.com ([7.191.163.213]) with mapi id 15.01.2507.031; Thu, 16 Nov 2023 14:06:03 +0000 From: Salil Mehta To: Cornelia Huck , Jianyong Wu , "maz@kernel.org" , "james.morse@arm.com" , "will@kernel.org" CC: "rmk@armlinux.org.uk" , "suzuki.poulose@arm.com" , "oliver.upton@linux.dev" , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "justin.he@arm.com" , "jianyong.wu@arm.com" Subject: RE: [PATCH] arm64/kvm: Introduce feature extension for SMCCC filter Thread-Topic: [PATCH] arm64/kvm: Introduce feature extension for SMCCC filter Thread-Index: AQHaGIJSPxqmEiVqkkOrXIqhoEeoZ7B86xkAgAAOImA= Date: Thu, 16 Nov 2023 14:06:03 +0000 Message-ID: <2ea495b04a7d484aa570059298e20862@huawei.com> References: <20231116114152.912344-1-jianyong.wu@arm.com> <877cmhq1zp.fsf@redhat.com> In-Reply-To: <877cmhq1zp.fsf@redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.48.150.188] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CFilter-Loop: Reflected > From: Cornelia Huck > Sent: Thursday, November 16, 2023 1:09 PM > To: Jianyong Wu ; maz@kernel.org; james.morse@arm.co= m; > will@kernel.org >=20 > On Thu, Nov 16 2023, Jianyong Wu wrote: >=20 > > 821d935c87b introduces support for userspace SMCCC filtering, but lack > > of a way to tell userspace if we have this feature. Add a corresponding > > feature extension can resolve this issue. > > > > For example, the incoming feature Vcpu Hotplug needs the SMCCC filter. > > As there is no way to check this feature, VMM will run into error when > > it calls this feature on an old kernel. It's bad for backward compatibl= e. >=20 > Can't you simply query via KVM_HAS_DEVICE_ATTR whether the SMCCC > filtering controls exist? Agreed. In fact, this is what I had earlier intended to do but deferred thi= s change. As of now, RFC V2 of vCPU Hotplug series does not have this check y= et while installing the SMCCC filters in KVM Host. Thanks > > Signed-off-by: Jianyong Wu > > --- > > Documentation/virt/kvm/api.rst | 3 ++- > > arch/arm64/kvm/arm.c | 1 + > > include/uapi/linux/kvm.h | 1 + > > 3 files changed, 4 insertions(+), 1 deletion(-) > >