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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id r11-20020a17090b050b00b001c741fd4890sm3627743pjz.9.2022.03.29.12.13.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Mar 2022 12:13:04 -0700 (PDT) Date: Tue, 29 Mar 2022 19:13:00 +0000 From: Sean Christopherson To: Chao Peng Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, qemu-devel@nongnu.org, Paolo Bonzini , Jonathan Corbet , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . 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 Subject: Re: [PATCH v5 12/13] KVM: Expose KVM_MEM_PRIVATE Message-ID: References: <20220310140911.50924-1-chao.p.peng@linux.intel.com> <20220310140911.50924-13-chao.p.peng@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220310140911.50924-13-chao.p.peng@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 10, 2022, Chao Peng wrote: > KVM_MEM_PRIVATE is not exposed by default but architecture code can turn > on it by implementing kvm_arch_private_memory_supported(). > > Signed-off-by: Yu Zhang > Signed-off-by: Chao Peng > --- > include/linux/kvm_host.h | 1 + > virt/kvm/kvm_main.c | 24 +++++++++++++++++++----- > 2 files changed, 20 insertions(+), 5 deletions(-) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 186b9b981a65..0150e952a131 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -1432,6 +1432,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu); > int kvm_arch_post_init_vm(struct kvm *kvm); > void kvm_arch_pre_destroy_vm(struct kvm *kvm); > int kvm_arch_create_vm_debugfs(struct kvm *kvm); > +bool kvm_arch_private_memory_supported(struct kvm *kvm); > > #ifndef __KVM_HAVE_ARCH_VM_ALLOC > /* > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 52319f49d58a..df5311755a40 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -1485,10 +1485,19 @@ static void kvm_replace_memslot(struct kvm *kvm, > } > } > > -static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem) > +bool __weak kvm_arch_private_memory_supported(struct kvm *kvm) > +{ > + return false; > +} > + > +static int check_memory_region_flags(struct kvm *kvm, > + const struct kvm_userspace_memory_region *mem) > { > u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES; > > + if (kvm_arch_private_memory_supported(kvm)) > + valid_flags |= KVM_MEM_PRIVATE; > + > #ifdef __KVM_HAVE_READONLY_MEM > valid_flags |= KVM_MEM_READONLY; > #endif > @@ -1900,7 +1909,7 @@ int __kvm_set_memory_region(struct kvm *kvm, > int as_id, id; > int r; > > - r = check_memory_region_flags(mem); > + r = check_memory_region_flags(kvm, mem); > if (r) > return r; > > @@ -1913,10 +1922,12 @@ int __kvm_set_memory_region(struct kvm *kvm, > return -EINVAL; > if (mem->guest_phys_addr & (PAGE_SIZE - 1)) > return -EINVAL; > - /* We can read the guest memory with __xxx_user() later on. */ > if ((mem->userspace_addr & (PAGE_SIZE - 1)) || > - (mem->userspace_addr != untagged_addr(mem->userspace_addr)) || > - !access_ok((void __user *)(unsigned long)mem->userspace_addr, > + (mem->userspace_addr != untagged_addr(mem->userspace_addr))) > + return -EINVAL; > + /* We can read the guest memory with __xxx_user() later on. */ > + if (!(mem->flags & KVM_MEM_PRIVATE) && > + !access_ok((void __user *)(unsigned long)mem->userspace_addr, This should sanity check private_offset for private memslots. At a bare minimum, wrapping should be disallowed. > mem->memory_size)) > return -EINVAL; > if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM) > @@ -1957,6 +1968,9 @@ int __kvm_set_memory_region(struct kvm *kvm, > if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages) > return -EINVAL; > } else { /* Modify an existing slot. */ > + /* Private memslots are immutable, they can only be deleted. */ > + if (mem->flags & KVM_MEM_PRIVATE) > + return -EINVAL; These sanity checks belong in "KVM: Register private memslot to memory backing store", e.g. that patch is "broken" without the immutability restriction. It's somewhat moot because the code is unreachable, but it makes reviewing confusing/difficult. But rather than move the sanity checks back, I think I'd prefer to pull all of patch 10 here. I think it also makes sense to drop "KVM: Use memfile_pfn_ops to obtain pfn for private pages" and add the pointer in "struct kvm_memory_slot" in patch "KVM: Extend the memslot to support fd-based private memory", with the use of the ops folded into "KVM: Handle page fault for private memory". Adding code to KVM and KVM-x86 in a single patch is ok, and overall makes things easier to review because the new helpers have a user right away, especially since there will be #ifdeffery. I.e. end up with something like: mm: Introduce memfile_notifier mm/shmem: Restrict MFD_INACCESSIBLE memory against RLIMIT_MEMLOCK KVM: Extend the memslot to support fd-based private memory KVM: Use kvm_userspace_memory_region_ext KVM: Add KVM_EXIT_MEMORY_ERROR exit KVM: Handle page fault for private memory KVM: Register private memslot to memory backing store KVM: Zap existing KVM mappings when pages changed in the private fd KVM: Enable and expose KVM_MEM_PRIVATE > if ((mem->userspace_addr != old->userspace_addr) || > (npages != old->npages) || > ((mem->flags ^ old->flags) & KVM_MEM_READONLY)) > -- > 2.17.1 >