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Date: Mon, 4 Jul 2016 15:59:33 +0800 From: Xiao Guangrong <guangrong.xiao@...ux.intel.com> To: Paolo Bonzini <pbonzini@...hat.com>, Neo Jia <cjia@...dia.com> Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, Kirti Wankhede <kwankhede@...dia.com>, Andrea Arcangeli <aarcange@...hat.com>, Radim Krčmář <rkrcmar@...hat.com> Subject: Re: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn_range-ed 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......
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