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Thu, 10 Sep 2020 02:39:03 -0400 X-MC-Unique: -LsA0AtMOamTxiuSwHlPFw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7147F1091061; Thu, 10 Sep 2020 06:39:01 +0000 (UTC) Received: from kamzik.brq.redhat.com (unknown [10.40.192.124]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B7CCB5C1CF; Thu, 10 Sep 2020 06:38:57 +0000 (UTC) Date: Thu, 10 Sep 2020 08:38:54 +0200 From: Andrew Jones To: Peter Maydell Subject: Re: [PATCH v2 2/2] arm64: kvm: Introduce MTE VCPU feature Message-ID: <20200910063854.vwhtn3lc5tei72fh@kamzik.brq.redhat.com> References: <20200904160018.29481-1-steven.price@arm.com> <20200904160018.29481-3-steven.price@arm.com> <20200909154804.mide6szbzgdy7jju@kamzik.brq.redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200910_023905_517763_4219989A X-CRM114-Status: GOOD ( 21.73 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Juan Quintela , Catalin Marinas , Richard Henderson , QEMU Developers , lkml - Kernel Mailing List , "Dr. David Alan Gilbert" , Marc Zyngier , Thomas Gleixner , Steven Price , Will Deacon , kvmarm@lists.cs.columbia.edu, arm-mail-list , Dave Martin Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Sep 09, 2020 at 04:53:02PM +0100, Peter Maydell wrote: > On Wed, 9 Sep 2020 at 16:48, Andrew Jones wrote: > > We either need a KVM cap or a new CPU feature probing interface to avoid > > making userspace try features one at a time. It's too bad that VCPU_INIT > > doesn't clear all offending features from the feature set when returning > > EINVAL, because then userspace could create a scratch VCPU with everything > > it supports in order to see what KVM also supports in one go. > > You could add one if you wanted -- add a new feature bit > TELL_ME_WHAT_YOU_HAVE. If the kernel sees that then on filure > it clears out feature bits it doesn't support and also clears > TELL_ME_WHAT_YOU_HAVE. If QEMU sees EINVAL and TELL_ME_WHAT_YOU_HAVE > is still set, then it knows it's dealing with an old kernel > and has to do one-at-a-time probing. If it sees EINVAL but not > TELL_ME_WHAT_YOU_HAVE then it knows it has a new kernel and > has just got all the info. > That's a great proposal. I'll try to find time to send the patches. Thanks, drew _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel