Re: [Xen-devel] [PATCH] x86/amd: Fix xen_apic_write warnings in Dom0

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.10.12 at 10:06, Wei Wang <wei.wang2@xxxxxxx> wrote:
>--- a/xen/arch/x86/cpu/amd.c
>+++ b/xen/arch/x86/cpu/amd.c
>@@ -485,6 +485,17 @@ static void __devinit init_amd(struct cpuinfo_x86 *c)
>       if (c->x86 > 0x11)
>               set_bit(X86_FEATURE_ARAT, c->x86_capability);
> 
>+      /* 
>+       * Prior to Family 0x14, perf counters are not reset during warm 
>reboot.  
>+       * We have to reset them manually.
>+       */
>+      if (c->x86 < 0x14) {
>+              wrmsrl(MSR_K7_PERFCTR0, 0);
>+              wrmsrl(MSR_K7_PERFCTR1, 0);
>+              wrmsrl(MSR_K7_PERFCTR2, 0);
>+              wrmsrl(MSR_K7_PERFCTR3, 0);
>+      }

This collides with the NMI watchdog setup: smp_callin() calls
setup_local_APIC() _before_ calling smp_store_cpu_info(), and
hence you write zero again to an MSR possibly already in use.
Since setup_k7_watchdog() itself does the clearing of the MSRs
in question already, I would think that the most simple
adjustment to your patch would be to make the condition

        if (nmi_watchdog != NMI_LOCAL_APIC && c->x86 < 0x14) {

If you agree (and Keir doesn't object), I would commit it that way.

Jan

>+
>       if (cpuid_edx(0x80000007) & (1 << 10)) {
>               rdmsr(MSR_K7_HWCR, l, h);
>               l |= (1 << 27); /* Enable read-only APERF/MPERF bit */



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