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Fri, 20 Aug 2021 12:46:16 +0000 (UTC) Received: from fuller.cnet (ovpn-112-5.gru2.redhat.com [10.97.112.5]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 602BD69CBC; Fri, 20 Aug 2021 12:46:16 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id AEDE0418AE12; Fri, 20 Aug 2021 09:46:11 -0300 (-03) Date: Fri, 20 Aug 2021 09:46:11 -0300 From: Marcelo Tosatti To: Oliver Upton Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, Paolo Bonzini , Sean Christopherson , Marc Zyngier , Peter Shier , Jim Mattson , David Matlack , Ricardo Koller , Jing Zhang , Raghavendra Rao Anata , James Morse , Alexandru Elisei , Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, Andrew Jones , Will Deacon , Catalin Marinas Subject: Re: [PATCH v7 3/6] KVM: x86: Report host tsc and realtime values in KVM_GET_CLOCK Message-ID: <20210820124611.GA77176@fuller.cnet> References: <20210816001130.3059564-1-oupton@google.com> <20210816001130.3059564-4-oupton@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210816001130.3059564-4-oupton@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210820_054622_479400_9D401F5C X-CRM114-Status: GOOD ( 14.69 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 Mon, Aug 16, 2021 at 12:11:27AM +0000, Oliver Upton wrote: > Handling the migration of TSCs correctly is difficult, in part because > Linux does not provide userspace with the ability to retrieve a (TSC, > realtime) clock pair for a single instant in time. In lieu of a more > convenient facility, KVM can report similar information in the kvm_clock > structure. > > Provide userspace with a host TSC & realtime pair iff the realtime clock > is based on the TSC. If userspace provides KVM_SET_CLOCK with a valid > realtime value, advance the KVM clock by the amount of elapsed time. Do > not step the KVM clock backwards, though, as it is a monotonic > oscillator. > > Suggested-by: Paolo Bonzini > Signed-off-by: Oliver Upton This is a good idea. Userspace could check if host and destination clocks are up to a certain difference and not use the feature if not appropriate. Is there a qemu patch for it? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel