Re: [Xen-devel] [PATCH v2 RFC 2/4] x86/PV: support data breakpoint extension registers

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 27.03.14 at 18:29, <Ian.Campbell@xxxxxxxxxx> wrote:
> On Thu, 2014-03-27 at 16:44 +0000, Jan Beulich wrote:
>> >>> On 27.03.14 at 17:23, <Ian.Campbell@xxxxxxxxxx> wrote:
>> > On Thu, 2014-03-27 at 16:03 +0000, Jan Beulich wrote:
>> >> >>> On 27.03.14 at 16:28, <Ian.Campbell@xxxxxxxxxx> wrote:
>> >> > How does N->N+1 migration work out?
>> >> 
>> >> Since the structure size grows, and that size is embedded in the
>> >> structure, input coming from N will be treated as not having any
>> >> MSRs.
>> > 
>> > This is the size of the "extv" block in the header phase?
>> 
>> No, the "size" member of struct xen_domctl_ext_vcpucontext.
> 
> OK, that makes sense.
> 
> Are you also breaking the 128b limit on the data returned by this
> struct?

Indirectly, not directly (by adding this pointer to outside the
structure). The 128-byte limit is the fundamental reason why a
separate array needs to be used here, and why therefore extra
data needs to follow the base structure in the save/restore
stream.

Jan


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