Re: [Xen-devel] [PATCH RFC 2/2] xen/pvh: enable mmu_update hypercall

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.10.14 at 13:30, <roger.pau@xxxxxxxxxx> wrote:
> El 16/10/14 a les 10.45, Jan Beulich ha escrit:
>> And not just that - I can't even see how this would work at present:
>> paging_write_guest_entry() uses
>> v->arch.paging.mode->write_guest_entry, yet that actor gets filled
>> by shadow code only. I don't currently see how for PVH, requiring
>> HAP, this wouldn't end up in NULL dereferences. Am I overlooking
>> some (non-grep-able) initialization of this and .cmpxchg_guest_entry?
> 
> It "works" because this is only used by the migration code, and the page
> that's modified is never of the type PGT_writable_page. Should I look
> into implementing this operations for HAP, or should I just prevent it's
> usage from do_mmu_update if the caller turns out to be a HAP guest?

Aiui the only operation you really need is MMU_MACHPHYS_UPDATE,
in which case I'd suggest simply denying requests of the other two
kinds for the time being (and not just for HAP callers, but for any
paging_mode_external() ones).

Jan


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