[PATCH 2/3] acpi/processor: sanitize _PDC buffer bits when running as Xen dom0

[Roger Pau Monne <roger.pau@citrix.com>]

The Processor _PDC buffer bits notify ACPI of the OS capabilities, and
so ACPI can adjust the return of other Processor methods taking the OS
capabilities into account.

When Linux is running as a Xen dom0, it's the hypervisor the entity
in charge of processor power management, and hence Xen needs to make
sure the capabilities reported in the _PDC buffer match the
capabilities of the driver in Xen.

Introduce a small helper to sanitize the buffer when running as Xen
dom0.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Cc: stable@vger.kernel.org
---
 arch/x86/include/asm/xen/hypervisor.h |  2 ++
 arch/x86/xen/enlighten.c              | 17 +++++++++++++++++
 drivers/acpi/processor_pdc.c          |  8 ++++++++
 3 files changed, 27 insertions(+)

diff --git a/arch/x86/include/asm/xen/hypervisor.h b/arch/x86/include/asm/xen/hypervisor.h
index b9f512138043..b4ed90ef5e68 100644
--- a/arch/x86/include/asm/xen/hypervisor.h
+++ b/arch/x86/include/asm/xen/hypervisor.h
@@ -63,12 +63,14 @@ void __init mem_map_via_hcall(struct boot_params *boot_params_p);
 
 #ifdef CONFIG_XEN_DOM0
 bool __init xen_processor_present(uint32_t acpi_id);
+void xen_sanitize_pdc(uint32_t *buf);
 #else
 static inline bool xen_processor_present(uint32_t acpi_id)
 {
 	BUG();
 	return false;
 }
+static inline void xen_sanitize_pdc(uint32_t *buf) { BUG(); }
 #endif
 
 #endif /* _ASM_X86_XEN_HYPERVISOR_H */
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index d4c44361a26c..394dd6675113 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -372,4 +372,21 @@ bool __init xen_processor_present(uint32_t acpi_id)
 
 	return false;
 }
+
+void xen_sanitize_pdc(uint32_t *buf)
+{
+	struct xen_platform_op op = {
+		.cmd			= XENPF_set_processor_pminfo,
+		.interface_version	= XENPF_INTERFACE_VERSION,
+		.u.set_pminfo.id	= -1,
+		.u.set_pminfo.type	= XEN_PM_PDC,
+	};
+	int ret;
+
+	set_xen_guest_handle(op.u.set_pminfo.pdc, buf);
+	ret = HYPERVISOR_platform_op(&op);
+	if (ret)
+		pr_info("sanitize of _PDC buffer bits from Xen failed: %d\n",
+		        ret);
+}
 #endif
diff --git a/drivers/acpi/processor_pdc.c b/drivers/acpi/processor_pdc.c
index 18fb04523f93..58f4c208517a 100644
--- a/drivers/acpi/processor_pdc.c
+++ b/drivers/acpi/processor_pdc.c
@@ -137,6 +137,14 @@ acpi_processor_eval_pdc(acpi_handle handle, struct acpi_object_list *pdc_in)
 		buffer[2] &= ~(ACPI_PDC_C_C2C3_FFH | ACPI_PDC_C_C1_FFH);
 
 	}
+	if (xen_initial_domain())
+		/*
+		 * When Linux is running as Xen dom0 it's the hypervisor the
+		 * entity in charge of the processor power management, and so
+		 * Xen needs to check the OS capabilities reported in the _PDC
+		 * buffer matches what the hypervisor driver supports.
+		 */
+		xen_sanitize_pdc((uint32_t *)pdc_in->pointer->buffer.pointer);
 	status = acpi_evaluate_object(handle, "_PDC", pdc_in, NULL);
 
 	if (ACPI_FAILURE(status))
-- 
2.37.3