Re: [Xen-devel] Xen 4.1 + Linux compiled with PVH == BOOM

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.01.14 at 12:31, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Tue, 2014-01-07 at 08:23 +0000, Jan Beulich wrote:
>> >> that feature statically in the first place - that should be done only if 
> the 
>> > kernel
>> >> could _only_ boot in PVH mode.
>> > 
>> > The feature is not marked as "required" but rather - it can utilize said
>> > extension (so supported). I am advocating that the calleer checks that
>> > all of the required pieces are correct - and it can ignore the ones it
>> > has no idea off (which it does for some of the Xen ELF notes - ignores
>> > them if it has no idea of what they are).
>> 
>> What would be to point of telling the hypervisor that the kernel
>> can utilize a certain extension? The kernel could just utilize it, and
>> the hypervisor would know by that simple fact.
> 
> But for PVH doesn't the hypervisor need to now at dom0 build time
> whether to build a PV or PVH domain?

Which needs to be communicated via hypervisor command line option
anyway. Specifying the option without have a suitable kernel is (of
course) a user error (generally expected to result in a kernel crash).

Jan

> So it needs to know upfront if the
> kernel could do PVH or not, and then pick, but once it has picked the
> kernel had best follow that choice.
> 
> So in the PVH case it's not just a simple case of the kernel deciding to
> utilize an optional feature, the optional feature has already been
> enabled.
> 
> Ian




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