Re: [Xen-devel] [PATCH] x86/HVM: tie RTC emulation mode to enabling of Viridian emulation

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.07.13 at 11:51, Tim Deegan <tim@xxxxxxx> wrote:
> At 10:27 +0100 on 02 Jul (1372760862), Jan Beulich wrote:
>> >>> On 02.07.13 at 11:11, Tim Deegan <tim@xxxxxxx> wrote:
>> > At 08:02 +0100 on 02 Jul (1372752161), Jan Beulich wrote:
>> >> As the mode not conforming to the hardware specification (by allowing
>> >> the guest to skip the REG C reads in its interrupt handler) is a
>> >> Viridian invention, it seems logical to tie this mode to that extension
>> >> being enabled. If the extension is disabled, proper hardware emulation
>> >> will be done instead.
>> >> 
>> >> The main thing necessary here is the synchronization of the RTC
>> >> emulation code and the setting of the respective flag in hvmloader's
>> >> creation of the ACPI WAET table.
>> >> 
>> >> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> > 
>> > Wasn't this going to have its own param, defaulting to off on create and
>> > to on on migrate?  I suspect most people just leave the viridian flag on
>> > for all domains.
>> 
>> In which case there would be no behavioral difference to what
>> we're going to release with 4.3. (That's leaving aside the fact that
>> I think people doing so is not the best practice.)
> 
> Why not?  The Viridian interfaces is pretty well essential for running
> recent Windows, and shouldn't be harmful for other OSes.

Shouldn't. But as we learned it occasionally is - Linux when built
without CONFIG_XEN_PVHVM detects the HyperV functionality,
and tried using HyperV functionality that Xen doesn't really emulate
(see commits 32068f65 ["x86: Hyper-V: register clocksource only if
its advertised"] and db34bbb7 ["X86: Add a check to catch Xen
emulation of Hyper-V"]).

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel