RE: [Xen-devel] [PATCH 3/5] vtdt: Modify vlapic code to add vtdt support

["Wei, Gang" <gang.wei@xxxxxxxxx>]

Keir Fraser wrote on 2010-12-14:
> On 14/12/2010 03:27, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:
> 
>> @@ -643,7 +669,11 @@ static int vlapic_write(struct vcpu *v,
>>          break;
>>      case APIC_LVTT:         /* LVT Timer Reg */
>> +        destroy_periodic_time(&vlapic->pt);
>>          vlapic->pt.irq = val & APIC_VECTOR_MASK;
>> +        vlapic_set_reg(vlapic, APIC_TMICT, 0);
>> +        vlapic_set_reg(vlapic, APIC_TMCCT, 0);
>> +        vlapic->hw.tdt_msr = 0;
> 
> Writing any value to LVTT zaps TMICT,TMCCT,MSR_TDT? That seems pretty
> unlikely to me! This obviously has effects on behaviour outside TDT
> emulation as it affects TMICT/TMCCT emulation. Looks dangerous, as well as 
> wrong.

It should be better to do the zaps only while the mode bits of LVTT changes.

> 
> Also I now notice that this patch is not against tip of xen-unstable,
> as these changes should be to new function vlapic_reg_write().

Sorry for that. I had rebased it to the tip, but happened to send out the old 
one. I will resend this patch.

Jimmy

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