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Tsirkin" To: Paolo Bonzini Cc: Ani Sinha , Sergio Lopez , Richard Henderson , Eduardo Habkost , Marcel Apfelbaum , Zhao Liu , imammedo@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH v2] microvm: do not use the lastest cpu version Message-ID: <20250318093227-mutt-send-email-mst@kernel.org> References: <20250220065326.312596-1-anisinha@redhat.com> <004396c0-8370-4015-b746-3c800f45984f@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <004396c0-8370-4015-b746-3c800f45984f@redhat.com> Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.332, 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_H2=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Mar 18, 2025 at 12:01:44PM +0100, Paolo Bonzini wrote: > On 2/20/25 07:53, Ani Sinha wrote: > > commit 0788a56bd1ae3 ("i386: Make unversioned CPU models be aliases") > > introduced 'default_cpu_version' for PCMachineClass. This created three > > categories of CPU models: > > - Most unversioned CPU models would use version 1 by default. > > - For machines 4.0.1 and older that do not support cpu model aliases, a > > special default_cpu_version value of CPU_VERSION_LEGACY is used. > > - It was thought that future machines would use the latest value of cpu > > versions corresponding to default_cpu_version value of > > CPU_VERSION_LATEST [1]. > > > > All pc machines still use the default cpu version of 1 for > > unversioned cpu models. CPU_VERSION_LATEST is a moving target and > > changes with time. > > Personally I believe this is a problem and I'd rather use CPU_VERSION_LATEST > for the unversioned pc and q35 models, just like microvm does. I don't object. > Unversioned models change the hardware properties and there's no reason for > CPU properties to be treated differently. Unversioned models are exactly > for when you are okay with a moving target. > > And independent of this, microvm could start having versioned variants, so > that pc and q35 work the same way. > > Paolo >