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Peter Anvin" , Hugh Dickins , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , "Kirill A . Shutemov" , luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, david@redhat.com, aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , Michael Roth , mhocko@suse.com Subject: Re: [PATCH v6 6/8] KVM: Handle page fault for private memory Content-Language: en-US To: Chao Peng , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, qemu-devel@nongnu.org References: <20220519153713.819591-1-chao.p.peng@linux.intel.com> <20220519153713.819591-7-chao.p.peng@linux.intel.com> From: "Nikunj A. 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To handle page faut for such access, KVM maps the > page only when this private property matches host's view on this page > which can be decided by checking whether the corresponding page is > populated in the private fd or not. A page is considered as private when > the page is populated in the private fd, otherwise it's shared. > > For a successful match, private pfn is obtained with memfile_notifier > callbacks from private fd and shared pfn is obtained with existing > get_user_pages. > > For a failed match, KVM causes a KVM_EXIT_MEMORY_FAULT exit to > userspace. Userspace then can convert memory between private/shared from > host's view then retry the access. > > Co-developed-by: Yu Zhang > Signed-off-by: Yu Zhang > Signed-off-by: Chao Peng > --- > arch/x86/kvm/mmu.h | 1 + > arch/x86/kvm/mmu/mmu.c | 70 +++++++++++++++++++++++++++++++-- > arch/x86/kvm/mmu/mmu_internal.h | 17 ++++++++ > arch/x86/kvm/mmu/mmutrace.h | 1 + > arch/x86/kvm/mmu/paging_tmpl.h | 5 ++- > include/linux/kvm_host.h | 22 +++++++++++ > 6 files changed, 112 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h > index 7e258cc94152..c84835762249 100644 > --- a/arch/x86/kvm/mmu.h > +++ b/arch/x86/kvm/mmu.h > @@ -176,6 +176,7 @@ struct kvm_page_fault { > > /* Derived from mmu and global state. */ > const bool is_tdp; > + const bool is_private; > const bool nx_huge_page_workaround_enabled; > > /* > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index afe18d70ece7..e18460e0d743 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -2899,6 +2899,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm, > if (max_level == PG_LEVEL_4K) > return PG_LEVEL_4K; > > + if (kvm_slot_is_private(slot)) > + return max_level; Can you explain the rationale behind the above change? AFAIU, this overrides the transparent_hugepage=never setting for both shared and private mappings. > host_level = host_pfn_mapping_level(kvm, gfn, pfn, slot); > return min(host_level, max_level); > } Regards Nikunj