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Thu, 10 Sep 2020 07:49:51 -0400 X-MC-Unique: SgqgcIBnNWOnuR5o4e7goA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6A6E9802B6C; Thu, 10 Sep 2020 11:49:49 +0000 (UTC) Received: from kamzik.brq.redhat.com (unknown [10.40.192.124]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EC8FF1A923; Thu, 10 Sep 2020 11:49:45 +0000 (UTC) Date: Thu, 10 Sep 2020 13:49:43 +0200 From: Andrew Jones To: Steven Price Subject: Re: [PATCH v2 2/2] arm64: kvm: Introduce MTE VCPU feature Message-ID: <20200910114943.cedbzlqfcgxg7jqs@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> <3a7e18af-84bd-cee3-d68f-e08f225fc166@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <3a7e18af-84bd-cee3-d68f-e08f225fc166@arm.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200910_074956_110052_E66FF916 X-CRM114-Status: GOOD ( 17.15 ) 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-devel@nongnu.org, "Dr. David Alan Gilbert" , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, Marc Zyngier , Thomas Gleixner , Will Deacon , Dave Martin , linux-kernel@vger.kernel.org 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 Thu, Sep 10, 2020 at 10:21:07AM +0100, Steven Price 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. > > If Peter's TELL_ME_WHAT_YOU_HAVE idea works out then perhaps we don't need > the cap? Or would it still be useful? > We wouldn't need it, but we don't _need_ it now either. It's not very convenient to probe vcpu features with scratch vcpus, especially if we must probe one at a time, but it works. The TELL_ME_WHAT_YOU_HAVE idea will only fix the one at a time issue, but still require a vcpu fd. If this feature becomes a VM feature then a cap or VM level API would help reduce the userspace probing work. Thanks, drew _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel