Re: [Xen-devel] [PATCH 2/2] x86/hvm/viridian: Enable APIC assist enlightenment

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.03.16 at 16:02, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx]
>> Sent: 15 March 2016 23:18
>> On Tue, Mar 15, 2016 at 04:14:16PM +0000, Paul Durrant wrote:
>> > +        domain_crash(v->domain);
>> > +
>> > +    v->arch.hvm_vcpu.viridian.apic_assist.vector = vector;
>> > +    *(uint32_t *)va |= 1u;
>> 
>> Oh my. What does that do? Why not 0xBADF00D
>> Is that prescriped in the spec?
> 
> The LSB is the only bit that has defined functionality. The next 31 bits are 
> reserved and the rest of the page is undefined.
> 
>> 
>> That looks quite unhealthy to do.
>> 
> 
> Reading the spec. again I do see that the reserved bits are defined to be 
> zero, so it looks like I can use = rather than |=.

Wouldn't that put at risk forward compatibility?

Jan


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