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Re: [Xen-devel] [PATCH 3/3] x86/mm-locks: apply a bias to lock levels for current domain

On Wed, Dec 19, 2018 at 12:17:51PM +0000, Andrew Cooper wrote:
> On 19/12/2018 12:10, Roger Pau Monné wrote:
> > Hypercalls AFAIK have a single target (or subject) domain, so even if
> > there's a stubdomain relation I'm not sure I see why that would
> > require this kind of locking, any domain can perform hypercalls
> > against a single subject domain, and the hypervisor itself doesn't
> > even know about stubdomain relations.
> Grant copy has two domains, and neither need to be the callee. 
> Specifically, we discovered during the SILO work that dom0 occasonally
> issues a dom1 => dom2 grant copy.

Grant copy doesn't attempt to lock multiple domains at the same time,
it takes a reference of each page and maps it into Xen address space,
but there's no cross domain mm locking at all AFAICT. It's indeed an
operation that *could* do interleaved domain locks, but it doesn't.


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