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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 26 Sep 2012, Mukesh Rathor wrote:
> On Mon, 24 Sep 2012 13:24:12 +0100
> Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> 
> > On Mon, 24 Sep 2012, Ian Campbell wrote:
> > > On Mon, 2012-09-24 at 12:55 +0100, Stefano Stabellini wrote:
> > > > There are few code style issues on this patch, I suggest you run
> > > > it through scripts/checkpatch.pl, it should be able to catch all
> > > > these errors.
> > > 
> > > It would also be nice to starting having some changelogs entries for
> > > these patches for the next posting. There's a lot of complex stuff
> > > > > +     return count;
> > > > 
> > > > Who is going to remove the corresponding mapping from the vma?
> > > > Also we might be able to replace the flush_tlb_all with a
> > > > flush_tlb_range.
> > > 
> > > 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);
> 

Right. So we should be able to get away without any tlb flushes in
xen_unmap_domain_mfn_range.

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