[Xen-devel] [PATCH 2/4] xen/apic: Return the APIC ID (and version) for CPU 0.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On x86_64 on AMD machines where the first APIC_ID is not zero, we get:

ACPI: LAPIC (acpi_id[0x01] lapic_id[0x10] enabled)
BIOS bug: APIC version is 0 for CPU 1/0x10, fixing up to 0x10
BIOS bug: APIC version mismatch, boot CPU: 0, CPU 1: version 10

which means that when the ACPI processor driver loads and
tries to parse the _Pxx states it fails to do as, as it
ends up calling acpi_get_cpuid which does this:

for_each_possible_cpu(i) {
        if (cpu_physical_id(i) == apic_id)
                return i;
}

And the bootup CPU, has not been found so it fails and returns -1
for the first CPU - which then subsequently in the loop that
"acpi_processor_get_info" does results in returning an error, which
means that "acpi_processor_add" failing and per_cpu(processor)
is never set (and is NULL).

That means that when xen-acpi-processor tries to load (much much
later on) and parse the P-states it gets -ENODEV from
acpi_processor_register_performance() (which tries to read
the per_cpu(processor)) and fails to parse the data.

Reported-by-and-Tested-by:  Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
Suggested-by:  Boris Ostrovsky <boris.ostrovsky@xxxxxxx>
[v2: Bit-shift APIC ID by 24 bits]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/enlighten.c |   35 ++++++++++++++++++++++++++++++++++-
 1 files changed, 34 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index a8f8844..4f437de 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -809,9 +809,40 @@ static void xen_io_delay(void)
 }
 
 #ifdef CONFIG_X86_LOCAL_APIC
+static unsigned long xen_set_apic_id(unsigned int x)
+{
+       WARN_ON(1);
+       return x;
+}
+static unsigned int xen_get_apic_id(unsigned long x)
+{
+       return ((x)>>24) & 0xFFu;
+}
 static u32 xen_apic_read(u32 reg)
 {
-       return 0;
+       struct xen_platform_op op = {
+               .cmd = XENPF_get_cpuinfo,
+               .interface_version = XENPF_INTERFACE_VERSION,
+               .u.pcpu_info.xen_cpuid = 0,
+       };
+       int ret = 0;
+
+       /* Shouldn't need this as APIC is turned off for PV, and we only
+        * get called on the bootup processor. But just in case. */
+       if (!xen_initial_domain() || smp_processor_id())
+               return 0;
+
+       if (reg == APIC_LVR)
+               return 0x10;
+
+       if (reg != APIC_ID)
+               return 0;
+
+       ret = HYPERVISOR_dom0_op(&op);
+       if (ret)
+               return 0;
+
+       return op.u.pcpu_info.apic_id << 24;
 }
 
 static void xen_apic_write(u32 reg, u32 val)
@@ -849,6 +880,8 @@ static void set_xen_basic_apic_ops(void)
        apic->icr_write = xen_apic_icr_write;
        apic->wait_icr_idle = xen_apic_wait_icr_idle;
        apic->safe_wait_icr_idle = xen_safe_apic_wait_icr_idle;
+       apic->set_apic_id = xen_set_apic_id;
+       apic->get_apic_id = xen_get_apic_id;
 }
 
 #endif
-- 
1.7.7.5


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