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Thu, 12 Feb 2026 06:42:59 -0800 (PST) X-Received: by 2002:a05:600c:848d:b0:471:114e:5894 with SMTP id 5b1f17b1804b1-483657166aemr44927195e9.25.1770907379248; Thu, 12 Feb 2026 06:42:59 -0800 (PST) From: Paolo Bonzini To: qemu-devel@nongnu.org Cc: Zhao Liu , Igor Mammedov Subject: [PULL 07/41] docs/specs/acpi_cpu_hotplug: Remove legacy cpu hotplug descriptions Date: Thu, 12 Feb 2026 15:42:09 +0100 Message-ID: <20260212144244.22579-8-pbonzini@redhat.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260212144244.22579-1-pbonzini@redhat.com> References: <20260212144244.22579-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.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, DKIMWL_WL_HIGH=-0.001, 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_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-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: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1770908072867158500 Content-Type: text/plain; charset="utf-8" From: Zhao Liu Legacy cpu hotplug has been removed totally and machines start with modern cpu hotplug interface directly. Therefore, update the documentation to describe current QEMU cpu hotplug logic. Reviewed-by: Igor Mammedov Signed-off-by: Zhao Liu Link: https://lore.kernel.org/r/20260108033051.777361-7-zhao1.liu@intel.com Signed-off-by: Paolo Bonzini --- docs/specs/acpi_cpu_hotplug.rst | 28 +++------------------------- 1 file changed, 3 insertions(+), 25 deletions(-) diff --git a/docs/specs/acpi_cpu_hotplug.rst b/docs/specs/acpi_cpu_hotplug.= rst index 351057c9676..f4967810004 100644 --- a/docs/specs/acpi_cpu_hotplug.rst +++ b/docs/specs/acpi_cpu_hotplug.rst @@ -8,22 +8,6 @@ ACPI BIOS GPE.2 handler is dedicated for notifying OS abou= t CPU hot-add and hot-remove events. =20 =20 -Legacy ACPI CPU hotplug interface registers -------------------------------------------- - -CPU present bitmap for: - -- ICH9-LPC (IO port 0x0cd8-0xcf7, 1-byte access) -- PIIX-PM (IO port 0xaf00-0xaf1f, 1-byte access) -- One bit per CPU. Bit position reflects corresponding CPU APIC ID. Read-o= nly. -- The first DWORD in bitmap is used in write mode to switch from legacy - to modern CPU hotplug interface, write 0 into it to do switch. - -QEMU sets corresponding CPU bit on hot-add event and issues SCI -with GPE.2 event set. CPU present map is read by ACPI BIOS GPE.2 handler -to notify OS about CPU hot-add events. CPU hot-remove isn't supported. - - Modern ACPI CPU hotplug interface registers ------------------------------------------- =20 @@ -189,20 +173,14 @@ Typical usecases (x86) Detecting and enabling modern CPU hotplug interface ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ =20 -QEMU starts with legacy CPU hotplug interface enabled. Detecting and -switching to modern interface is based on the 2 legacy CPU hotplug feature= s: +QEMU starts with modern CPU hotplug interface enabled. Use following steps= to +detect modern CPU hotplug interface: =20 -#. Writes into CPU bitmap are ignored. -#. CPU bitmap always has bit #0 set, corresponding to boot CPU. - -Use following steps to detect and enable modern CPU hotplug interface: - -#. Store 0x0 to the 'CPU selector' register, attempting to switch to moder= n mode #. Store 0x0 to the 'CPU selector' register, to ensure valid selector value #. Store 0x0 to the 'Command field' register #. Read the 'Command data 2' register. If read value is 0x0, the modern interface is enabled. - Otherwise legacy or no CPU hotplug interface available + Otherwise no CPU hotplug interface available =20 Get a cpu with pending event ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ --=20 2.52.0