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

[Keir Fraser <keir.xen@gmail.com>]

On 15/10/2012 12:12, "Jan Beulich" <JBeulich@suse.com> wrote:

>>>> On 09.10.12 at 10:06, Wei Wang <wei.wang2@amd.com> 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.

Sounds good.

Acked-by: Keir Fraser <keir@xen.org>

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