[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v4 2/2] x86/PV: support data breakpoint extension registers
>>> On 23.04.14 at 14:39, <Ian.Campbell@xxxxxxxxxxxxx> wrote: > On Wed, 2014-04-23 at 13:35 +0100, Jan Beulich wrote: >> >>> On 23.04.14 at 14:23, <Ian.Campbell@xxxxxxxxxxxxx> wrote: >> > All makes sense. Worth a comment though? >> >> Not sure - it's no more subtle than other code in the handling of that >> specific sub-hypercall. But yes, by my own argumentation elsewhere >> maybe I shouldn't be extending badness - if only I saw ways of >> describing things like this without just converting C to human language >> (which doesn't seem all that helpful)... > > Nothing the behaviour of msr_count you describe doesn't sound like just > converting the C to human readable to me, unless you expect readers of > this interface header to go digging into the implementation to figure > this out, which shouldn't be needed (that's the point of docs after all!) Oh, right, I didn't realize your comment was in the context of the public header changes - I blindly assumed them to be on the code implementing the interface extension. Will see to put something like the above in there. >> >> So as is the tools are fine not explicitly setting msr_count (it's being >> >> implicitly set to zero) - state save will fail in that case. It's the 3rd >> >> (unfinished and now delayed until after Andrew's re-write) patch >> >> that would be dealing with that error, re-issuing the call after >> >> allocating a suitable array. >> > >> > That would be a bisection hazard wouldn't it? >> >> Only with guests using the extension and wanting to be migrated. > > I hadn't realised there was this condition as well (since hte feature > looks more generic at the level I'm looking at it). > > So any such guests would fail to migrate today anyway, right? I think such a guest wouldn't make it to migration, but would rather be killed (by sending it a #GP it may not expect) for an invalid MSR write. I.e. the improvement of this patch is to make it work at all, but fail on attempts to be migrated. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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