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Wed, 8 Jul 2020 16:03:17 +0000 (UTC) Date: Wed, 8 Jul 2020 12:03:16 -0400 From: Eduardo Habkost To: Peter Maydell Subject: Re: [PATCH] cpu: Add starts_halted() method Message-ID: <20200708160316.GA7276@habkost.net> References: <20200707204333.261506-1-bauerman@linux.ibm.com> <20200707214917.GX7276@habkost.net> <87y2nu3nxq.fsf@morokweng.localdomain> <20200708100038.GG18595@umbus.fritz.box> <20200708152540.GZ7276@habkost.net> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=ehabkost@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=ehabkost@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/07 17:25:09 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Laurent Vivier , Thomas Huth , Alex =?iso-8859-1?Q?Benn=E9e?= , QEMU Developers , qemu-ppc , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Thiago Jung Bauermann , David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 08, 2020 at 04:32:51PM +0100, Peter Maydell wrote: > On Wed, 8 Jul 2020 at 16:25, Eduardo Habkost wrote: > > On Wed, Jul 08, 2020 at 02:14:03PM +0100, Peter Maydell wrote: > > > The original bug as described in the commit message sounds > > > to me like something we should look to fix in the implementation > > > of async_run_on_cpu() -- it shouldn't cause a CPU that's halfway > > > through reset to do a KVM_RUN or otherwise run guest code, > > > whether that CPU is going to start powered-up or powered-down. > > > > What "halfway through reset" means, exactly? Isn't halted==1 > > enough to indicate the CPU is in that state? > > I mean "while we're in the middle of the CPU method that's > called by cpu_reset()". "halted==1" says "the CPU is halted"; > that's not the same thing. KVM_RUN happening > as a side effect in the middle of that code is a bug > whether the CPU happens to be intended to be put into the > halted state or not. If the CPU is intended to be created > not-halted then KVM_RUN can happen after cpu reset > completes, but not before. Wait, I thought we already had mechanisms to prevent that from happening. Otherwise, it would never be safe for cpu_reset() to touch the CPU registers. -- Eduardo