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From:   Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
To:     linux-pm@vger.kernel.org, loongarch@lists.linux.dev,
        linux-acpi@vger.kernel.org, linux-arch@vger.kernel.org,
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Cc:     Salil Mehta <salil.mehta@huawei.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        jianyong.wu@arm.com, justin.he@arm.com,
        James Morse <james.morse@arm.com>
Subject: [PATCH RFC v3 10/21] ACPI: Check _STA present bit before making CPUs
 not present
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Sender: Russell King <rmk@armlinux.org.uk>
Date:   Wed, 13 Dec 2023 12:50:02 +0000
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From: James Morse <james.morse@arm.com>

When called acpi_processor_post_eject() unconditionally make a CPU
not-present and unregisters it.

To add support for AML events where the CPU has become disabled, but
remains present, the _STA method should be checked before calling
acpi_processor_remove().

Rename acpi_processor_post_eject() acpi_processor_remove_possible(), and
check the _STA before calling.

Adding the function prototype for arch_unregister_cpu() allows the
preprocessor guards to be removed.

After this change CPUs will remain registered and visible to
user-space as offline if buggy firmware triggers an eject-request,
but doesn't clear the corresponding _STA bits after _EJ0 has been
called.

Signed-off-by: James Morse <james.morse@arm.com>
Tested-by: Miguel Luis <miguel.luis@oracle.com>
Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
Tested-by: Jianyong Wu <jianyong.wu@arm.com>
---
Changes since RFC v3:
 * Move IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU) into separate patch.
Outstanding comments:
 https://lore.kernel.org/r/20230914153110.00003e38@Huawei.com
 https://lore.kernel.org/r/518859b1-64a9-d723-963c-56c7f6fc2da1@redhat.com
  This contains a repeat of the IS_ENABLED() issue which we don't think
  is a problem - but there is another issue mentioned in that comment.
---
 drivers/acpi/acpi_processor.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index 01c460881662..19fceb3ec4e2 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -458,16 +458,13 @@ static int acpi_processor_add(struct acpi_device *device,
 }
 
 /* Removal */
-static void acpi_processor_post_eject(struct acpi_device *device)
+static void acpi_processor_make_not_present(struct acpi_device *device)
 {
 	struct acpi_processor *pr;
 
 	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU))
 		return;
 
-	if (!device || !acpi_driver_data(device))
-		return;
-
 	pr = acpi_driver_data(device);
 	if (pr->id >= nr_cpu_ids)
 		goto out;
@@ -504,6 +501,29 @@ static void acpi_processor_post_eject(struct acpi_device *device)
 	kfree(pr);
 }
 
+static void acpi_processor_post_eject(struct acpi_device *device)
+{
+	struct acpi_processor *pr;
+	unsigned long long sta;
+	acpi_status status;
+
+	if (!device)
+		return;
+
+	pr = acpi_driver_data(device);
+	if (!pr || pr->id >= nr_cpu_ids || invalid_phys_cpuid(pr->phys_id))
+		return;
+
+	status = acpi_evaluate_integer(pr->handle, "_STA", NULL, &sta);
+	if (ACPI_FAILURE(status))
+		return;
+
+	if (cpu_present(pr->id) && !(sta & ACPI_STA_DEVICE_PRESENT)) {
+		acpi_processor_make_not_present(device);
+		return;
+	}
+}
+
 #ifdef CONFIG_ARCH_MIGHT_HAVE_ACPI_PDC
 bool __init processor_physically_present(acpi_handle handle)
 {
-- 
2.30.2