Re: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn_range-ed

[Xiao Guangrong]

On 07/04/2016 03:48 PM, Paolo Bonzini wrote:
> On 04/07/2016 09:37, Xiao Guangrong wrote:
> > > >
> > >
> > > It actually is a portion of the physical mmio which is set by vfio mmap.
> >
> > So i do not think we need to care its refcount, i,e, we can consider it
> > as reserved_pfn,
> > Paolo?
>
> nVidia provided me (offlist) with a simple patch that modified VFIO to
> exhibit the problem, and it didn't use reserved PFNs.  This is why the
> commit message for the patch is not entirely accurate.

It's clear now.

> But apart from this, it's much more obvious to consider the refcount.
> The x86 MMU code doesn't care if the page is reserved or not;
> mmu_set_spte does a kvm_release_pfn_clean, hence it makes sense for
> hva_to_pfn_remapped to try doing a get_page (via kvm_get_pfn) after
> invoking the fault handler, just like the get_user_pages family of
> function does.

Well,  it's little strange as you always try to get refcont
for a PFNMAP region without MIXEDMAP which indicates all the memory
in this region is no 'struct page' backend.

But it works as kvm_{get, release}_* have already been aware of
reserved_pfn, so i am okay with it......