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Tue, 09 Feb 2021 11:23:14 -0800 (PST) Received: from localhost ([2601:647:4600:11e1:d2fd:ba5d:619c:c25d]) by smtp.gmail.com with ESMTPSA id q196sm11303492pfc.162.2021.02.09.11.23.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Feb 2021 11:23:14 -0800 (PST) From: Isaku Yamahata X-Google-Original-From: Isaku Yamahata Date: Tue, 9 Feb 2021 11:23:05 -0800 To: Igor Mammedov Subject: Re: [PATCH v2 3/9] acpi/core: always set SCI_EN when SMM isn't supported Message-ID: <20210209192305.GA28049@private.email.ne.jp> References: <20210209160514.0e015448@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210209160514.0e015448@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Received-SPF: pass client-ip=2607:f8b0:4864:20::431; envelope-from=yamahata.qemudev@gmail.com; helo=mail-pf1-x431.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Isaku Yamahata , philmd@redhat.com, qemu-devel@nongnu.org, isaku.yamahata@gmail.com, mst@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Feb 09, 2021 at 04:05:14PM +0100, Igor Mammedov wrote: > On Mon, 8 Feb 2021 13:57:22 -0800 > isaku.yamahata@gmail.com wrote: > > > From: Isaku Yamahata > > > > If SMM is not supported, ACPI fixed hardware doesn't support > > legacy-mode. ACPI-only platform. Where SCI_EN in PM1_CNT register is > > always set. > > The bit tells OS legacy mode(SCI_EN cleared) or ACPI mode(SCI_EN set). > > does it break some specific software? With the next patch (setting fadt.smi_cmd = 0 when smm isn't supported), guest Linux tries to switch to ACPI mode, finds smi_cmd = 0, and then fails to initialize acpi subsystem. will update the commit message in next respin. > > ACPI spec 4.8.10.1 PM1 Event Grouping > > PM1 Eanble Registers > > > For ACPI-only platforms (where SCI_EN is always set) > > > > Signed-off-by: Isaku Yamahata > it changes guest ABI for old machine types but it seems to me that > it's harmless (in typical use-cases backward and forward migrated > guest should work fine). > > The only thing that is broken is transitioning to legacy mode > when guest was started on old QEMU and then migrated to the new one > where disable op will be NOP and qemu always stays in ACPI mode > (so guest will hang while it waits for transition to happen). The patch affects guests only when SMM isn't supported. Concretely - user explicitly specified to disable smm by -machine smm=off or - underlying kvm doesn't have KVM_CAP_X86_SMM (smm=auto: default) Please refer to x86_machine_is_smm_enabled(). Also Libvirt checks if guest bios requires SMI and enables smm even when user disabling SMM. qemuFirmwareEnableFeatures() If smm is disabled and legacy-mode is enabled without this patch, SMI won't be injected to guest anyway. Thus guest breaks already. > Can you test this scenario with various guest OSes (old/new/MS Windows) > to check if it won't break them. Unless -machine smm=off is explicitly passed, this patch won't break guests. And such case is rare as I described above. My motivation for this patch series is preparation for TDX which disallows SMM mode and SMI injection. > if we are to be conservative, we need to disable this compliance fix > on old machine types. I'm fine with adding one more knob to be on safe side. -machine smm=off is such knob, though. Thanks, -- Isaku Yamahata