Re: [Xen-devel] [PATCH v2] x86/hvm/viridian: fix the TLB flush hypercall

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.03.16 at 18:35, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: 16 March 2016 15:36
>> >>> On 16.03.16 at 15:21, <paul.durrant@xxxxxxxxxx> wrote:
>> > @@ -656,7 +647,9 @@ int viridian_hypercall(struct cpu_user_regs *regs)
>> >           * so we may unnecessarily IPI some CPUs.
>> >           */
>> >          if ( !cpumask_empty(pcpu_mask) )
>> > -            flush_tlb_mask(pcpu_mask);
>> > +            smp_send_event_check_mask(pcpu_mask);
>> > +
>> > +        output.rep_complete = input.rep_count;
>> 
>> Questions on this one remain: Why only for this hypercall? And
>> what does "repeat count" mean in this context?
>> 
> 
> It's only for this hypercall because it's the only 'rep' hypercall we 
> implement. For non-rep hypercalls the spec states that the rep count and 
> starting index in the input params must be zero. It does not state what the 
> value of reps complete should be on output for non-rep hypercalls but I think 
> it's safe to assume that zero is correct.
> For rep hypercalls the spec says that on output "the reps complete field is 
> the total number of reps complete and not relative to the rep start index. 
> For example, if the caller specified a rep start index of 5, and a rep count 
> of 10, the reps complete field would indicate 10 upon successful completion".
> 
> Section 12.4.3 of the spec defines the HvFlushVirtualAddressList hypercall 
> as a rep hypercall and each rep refers to flush of a single guest VA range. 
> Because we invalidate all VA ranges in one go clearly we complete all reps 
> straight away :-)

Ah, there's an address list associated with it. So if the flush
request was just for a single page, isn't a flush-all then pretty
heavy handed?

Jan


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