Re: [Xen-devel] [PATCH v1 2/8]: PVH mmu changes

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Wed, Sep 26, 2012 at 1:27 AM, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
>> > I'm not convinced that a guest level TLB flush is either necessary
>> > or sufficient here. What we are doing is removing entries from the
>> > P2M which means that we need to do the appropriate HAP flush in the
>> > hypervisor, which must necessarily invalidate any stage 1 mappings
>> > which this flush might also touch (i.e. the HAP flush must be a
>> > super set of this flush).
>> >
>> > Without the HAP flush in the hypervisor you risk guests being able
>> > to see old p2m mappings via the TLB entries which is a security
>> > issue AFAICT.
>>
>> Yes, you are right, we need a flush in the hypervisor to flush the
>> EPT. It could probably live in the implementation of
>> XENMEM_add_to_physmap.
>>
>> This one should be just for the vma mappings, so in the case of
>> xen_unmap_domain_mfn_range is unnecessary (given that it is
>> not removing the vma mappings).
>
>
> My head spins looking at INVEPT and INVVPID docs, but doesn't it already
> happen in ept_set_entry():
>
>     if ( needs_sync )
>         ept_sync_domain(p2m->domain);

Yes, the point of having a clean p2m interface is that you shouldn't
need to figure out when to do hap flushes.

 -George

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