x86/apic: do not initialize LDR and DFR for bigsmp

Legacy apic init uses bigsmp for smp systems with 8 and more CPUs. The
bigsmp APIC implementation uses physical destination mode, but it
nevertheless initializes LDR and DFR. The LDR even ends up incorrectly with
multiple bit being set.

This does not cause a functional problem because LDR and DFR are ignored
when physical destination mode is active, but it triggered a problem on a
32-bit KVM guest which jumps into a kdump kernel.

The multiple bits set unearthed a bug in the KVM APIC implementation. The
code which creates the logical destination map for VCPUs ignores the
disabled state of the APIC and ends up overwriting an existing valid entry
and as a result, APIC calibration hangs in the guest during kdump
initialization.

Remove the bogus LDR/DFR initialization.

This is not intended to work around the KVM APIC bug. The LDR/DFR
ininitalization is wrong on its own.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Bandan Das <bsd@redhat.com>
[Linux commit bae3a8d3308ee69a7dbdf145911b18dfda8ade0d]

Drop init_apic_ldr_x2apic_phys() at the same time.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/arch/x86/genapic/delivery.c b/xen/arch/x86/genapic/delivery.c
index a86b8c94221730f4603739197280ac2939f8cdc5..36ef033e65685056abb919c81e716e8d33967f46 100644 (file)
--- a/xen/arch/x86/genapic/delivery.c
+++ b/xen/arch/x86/genapic/delivery.c
@@ -40,11 +40,7 @@ unsigned int cpu_mask_to_apicid_flat(const cpumask_t *cpumask)
 
 void init_apic_ldr_phys(void)
 {
-       unsigned long val;
-       apic_write(APIC_DFR, APIC_DFR_FLAT);
-       /* A dummy logical ID should be fine. We only deliver in phys mode. */
-       val = apic_read(APIC_LDR) & ~APIC_LDR_MASK;
-       apic_write(APIC_LDR, val);
+       /* We only deliver in phys mode - no setup needed. */
 }
 
 void __init clustered_apic_check_phys(void)

diff --git a/xen/arch/x86/genapic/x2apic.c b/xen/arch/x86/genapic/x2apic.c
index 74907e6002661f09e9f3802f352cce3840a1f2d0..d5a17f10d5cc9944a7454c6d7447af4df2a73aae 100644 (file)
--- a/xen/arch/x86/genapic/x2apic.c
+++ b/xen/arch/x86/genapic/x2apic.c
@@ -38,10 +38,6 @@ static inline u32 x2apic_cluster(unsigned int cpu)
     return per_cpu(cpu_2_logical_apicid, cpu) >> 16;
 }
 
-static void init_apic_ldr_x2apic_phys(void)
-{
-}
-
 static void init_apic_ldr_x2apic_cluster(void)
 {
     unsigned int cpu, this_cpu = smp_processor_id();
@@ -167,7 +163,7 @@ static const struct genapic __initconstrel apic_x2apic_phys = {
     APIC_INIT("x2apic_phys", NULL),
     .int_delivery_mode = dest_Fixed,
     .int_dest_mode = 0 /* physical delivery */,
-    .init_apic_ldr = init_apic_ldr_x2apic_phys,
+    .init_apic_ldr = init_apic_ldr_phys,
     .clustered_apic_check = clustered_apic_check_x2apic,
     .vector_allocation_cpumask = vector_allocation_cpumask_phys,
     .cpu_mask_to_apicid = cpu_mask_to_apicid_phys,