[Xen-devel] [PATCH 1/2] xen/apic: Provide Xen-specific version of cpu_present_to_apicid APIC op

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

Currently Xen uses default_cpu_present_to_apicid() which will always
report BAD_APICID for PV guests since x86_bios_cpu_apic_id is initialised
to that value and is never updated.

With commit 1f12e32f4cd5 ("x86/topology: Create logical package id"), this
op is now called by smp_init_package_map() when deciding whether to call
topology_update_package_map() which sets cpu_data(cpu).logical_proc_id.
The latter (as topology_logical_package_id(cpu)) may be used, for example,
by cpu_to_rapl_pmu() as an array index. Since uninitialized
logical_package_id is set to -1, the index will become 64K which is
obviously problematic.

While RAPL code (and any other users of logical_package_id) should be
careful in their assumptions about id's validity, Xen's
cpu_present_to_apicid op should still provide value consistent with its
own xen_apic_read(APIC_ID).

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 arch/x86/xen/apic.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/apic.c b/arch/x86/xen/apic.c
index abf4901..db52a7f 100644
--- a/arch/x86/xen/apic.c
+++ b/arch/x86/xen/apic.c
@@ -66,7 +66,7 @@ static u32 xen_apic_read(u32 reg)
 
        ret = HYPERVISOR_platform_op(&op);
        if (ret)
-               return 0;
+               op.u.pcpu_info.apic_id = BAD_APICID;
 
        return op.u.pcpu_info.apic_id << 24;
 }
@@ -142,6 +142,14 @@ static void xen_silent_inquire(int apicid)
 {
 }
 
+static int xen_cpu_present_to_apicid(int cpu)
+{
+       if (cpu_present(cpu))
+               return xen_get_apic_id(xen_apic_read(APIC_ID));
+       else
+               return BAD_APICID;
+}
+
 static struct apic xen_pv_apic = {
        .name                           = "Xen PV",
        .probe                          = xen_apic_probe_pv,
@@ -162,7 +170,7 @@ static struct apic xen_pv_apic = {
 
        .ioapic_phys_id_map             = default_ioapic_phys_id_map, /* Used 
on 32-bit */
        .setup_apic_routing             = NULL,
-       .cpu_present_to_apicid          = default_cpu_present_to_apicid,
+       .cpu_present_to_apicid          = xen_cpu_present_to_apicid,
        .apicid_to_cpu_present          = physid_set_mask_of_physid, /* Used on 
32-bit */
        .check_phys_apicid_present      = default_check_phys_apicid_present, /* 
smp_sanity_check needs it */
        .phys_pkg_id                    = xen_phys_pkg_id, /* detect_ht */
-- 
1.7.1


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