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Hi,
this ist the second version of the patch. I improved the comment, changed
nmi->pmc in some names and worked in Jan's notes.
Thanks.
Dietmar.
Fix an issue on Nehalem cpus where performance counter overflows may lead to
endless interrupt loops on this cpu.
Signed-off-by: Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>
diff -r 117d82dcd6ba -r 387427bfd6f7 xen/arch/x86/hvm/vmx/vpmu_core2.c
--- a/xen/arch/x86/hvm/vmx/vpmu_core2.c Fri Nov 19 18:55:18 2010 +0000
+++ b/xen/arch/x86/hvm/vmx/vpmu_core2.c Mon Nov 22 10:28:15 2010 +0100
@@ -36,6 +36,68 @@
#include <asm/hvm/vpmu.h>
#include <asm/hvm/vmx/vpmu_core2.h>
+/*
+ * QUIRK to workaround an issue on Nehalem processors currently seen
+ * on family 6 cpus E5520 (model 26) and X7542 (model 46).
+ * The issue leads to endless PMC interrupt loops on the processor.
+ * If the interrupt handler is running and a pmc reaches the value 0, this
+ * value remains forever and it triggers immediately a new interrupt after
+ * finishing the handler.
+ * A workaround is to read all flagged counters and if the value is 0 write
+ * 1 (or another value != 0) into it.
+ * There exist no errata and the real cause of this behaviour is unknown.
+ */
+static int is_pmc_quirk;
+
+static void check_pmc_quirk(void)
+{
+ u8 family = current_cpu_data.x86;
+ u8 cpu_model = current_cpu_data.x86_model;
+ is_pmc_quirk = 0;
+ if ( family == 6 )
+ {
+ if ( cpu_model == 46 || cpu_model == 26 )
+ is_pmc_quirk = 1;
+ }
+}
+
+static int core2_get_pmc_count(void);
+static void handle_pmc_quirk(u64 msr_content)
+{
+ int num_gen_pmc = core2_get_pmc_count();
+ int num_fix_pmc = 3;
+ int i;
+ u64 val;
+
+ if ( !is_pmc_quirk )
+ return;
+
+ val = msr_content;
+ for ( i = 0; i < num_gen_pmc; i++ )
+ {
+ if ( val & 0x1 )
+ {
+ u64 cnt;
+ rdmsrl(MSR_P6_PERFCTR0 + i, cnt);
+ if ( cnt == 0 )
+ wrmsrl(MSR_P6_PERFCTR0 + i, 1);
+ }
+ val >>= 1;
+ }
+ val = msr_content >> 32;
+ for ( i = 0; i < num_fix_pmc; i++ )
+ {
+ if ( val & 0x1 )
+ {
+ u64 cnt;
+ rdmsrl(MSR_CORE_PERF_FIXED_CTR0 + i, cnt);
+ if ( cnt == 0 )
+ wrmsrl(MSR_CORE_PERF_FIXED_CTR0 + i, 1);
+ }
+ val >>= 1;
+ }
+}
+
u32 core2_counters_msr[] = {
MSR_CORE_PERF_FIXED_CTR0,
MSR_CORE_PERF_FIXED_CTR1,
@@ -494,6 +556,10 @@
rdmsrl(MSR_CORE_PERF_GLOBAL_STATUS, msr_content);
if ( !msr_content )
return 0;
+
+ if ( is_pmc_quirk )
+ handle_pmc_quirk(msr_content);
+
core2_vpmu_cxt->global_ovf_status |= msr_content;
msr_content = 0xC000000700000000 | ((1 << core2_get_pmc_count()) - 1);
wrmsrl(MSR_CORE_PERF_GLOBAL_OVF_CTRL, msr_content);
@@ -515,6 +581,7 @@
static void core2_vpmu_initialise(struct vcpu *v)
{
+ check_pmc_quirk();
}
static void core2_vpmu_destroy(struct vcpu *v)
--
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