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From: "Jan Beulich" <JBeulich@suse.com>
To: Paul Durrant <Paul.Durrant@citrix.com>
Cc: Andrew Cooper <Andrew.Cooper3@citrix.com>,
	"Keir(Xen.org)" <keir@xen.org>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v2] x86/hvm/viridian: fix the TLB flush hypercall
Date: Thu, 17 Mar 2016 02:11:41 -0600	[thread overview]
Message-ID: <56EA74CD02000078000DD96E@prv-mh.provo.novell.com> (raw)
In-Reply-To: <c000f4d585604e8f98bedbb100e0a2b2@AMSPEX02CL03.citrite.net>

>>> On 16.03.16 at 18:35, <Paul.Durrant@citrix.com> wrote:
>> From: Jan Beulich [mailto:JBeulich@suse.com]
>> Sent: 16 March 2016 15:36
>> >>> On 16.03.16 at 15:21, <paul.durrant@citrix.com> 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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  reply	other threads:[~2016-03-17  8:11 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-16 14:21 Paul Durrant
2016-03-16 15:35 ` Jan Beulich
2016-03-16 17:35   ` Paul Durrant
2016-03-17  8:11     ` Jan Beulich [this message]
2016-03-17  8:14       ` Paul Durrant
2016-03-17  8:35 ` Jan Beulich
2016-03-17 10:30   ` Andrew Cooper

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