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

[Xiao Guangrong]

On 07/04/2016 04:14 PM, Paolo Bonzini wrote:
> On 04/07/2016 09:59, Xiao Guangrong wrote:
> > > 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.
>
> Fair enough, I can modify the comment.
>
> 	/*
> 	 * In case the VMA has VM_MIXEDMAP set, whoever called remap_pfn_range
> 	 * is also going to call e.g. unmap_mapping_range before the underlying
> 	 * non-reserved pages are freed, which will then call our MMU notifier.
> 	 * We still have to get a reference here to the page, because the callers
> 	 * of *hva_to_pfn* and *gfn_to_pfn* ultimately end up doing a
> 	 * kvm_release_pfn_clean on the returned pfn.  If the pfn is
> 	 * reserved, the kvm_get_pfn/kvm_release_pfn_clean pair will simply
> 	 * do nothing.
> 	 */

Excellent. I like it. :)