Re: [PATCH 2/2] KVM: VMX: Initialize vm86 TSS only once.

[Avi Kivity <avi@redhat.com>]

On 02/27/2011 05:58 PM, Avi Kivity wrote:
>
>> The problem with using top of slot
>> zero is that this memory is available for guest use and we do not even
>> put it into e820 map as far as I see. Also there are patches floating
>> around that re-arrange memslots or even put them in a tree. They will
>> break old guests too.
>
> Well, slot 0 still exists even if it is moved somewhere else.
>
> Something we can do is put the tss slot just below the highest slot 
> that is still below 4G, and hope there is no mmio there.  Once the 
> user issues KVM_SET_TSS_ADDR, use that.  We'll have to keep juggling 
> that slot as the user creates more slots, icky.
>

Or we can keep the old behaviour.  If KVM_SET_TSS_ADDR hasn't been 
called by the time of the first entry into real mode (the first 
KVM_CREATE_VCPU?), use the top of the first slot.

We can avoid the SMP problem by initializing the memory in a single 
pass, writing each byte exactly once with its final value.  This way 
concurrent initialization doesn't corrupt an in-use TSS.

-- 
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