Re: [Xen-devel] [PATCH] VMX virtual-apic: Update the p2m mapping alongside the control bit

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 26/05/2010 09:57, "Tim Deegan" <Tim.Deegan@xxxxxxxxxxxxx> wrote:

>> The dummy data page should not be migrated because it has p2m type
>> mmio_direct, which will fail the p2m_is_ram() check in mod_l1_entry() when
>> dom0 attempts to map the page to save/migrate it.
> 
> Ah, so it will; I hadn't seen that.  The full failure mode is actually
> on migrating from Xen 3.3 (where mod_l1_entry() didn't have that check)
> to a newer Xen on a machine where the HW APIC virt isn't supported.  The
> sender sends the contents of the dummy page (incorrectly) and the
> receiver doesn't do anything (assuming that there'll be a hole in the
> p2m where the APIC should be).

Well, even so, the patch would still appear to only clear the p2m entry if
the APIC is disabled or relocated. Why would either be the case during
save/migrate?

Anyway, somewhat academic given we agree it's not needed at all in 3.4+

 -- Keir



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