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[34.168.104.7]) by smtp.gmail.com with ESMTPSA id k15-20020aa7972f000000b0056bbba4302dsm11324389pfg.119.2022.11.16.14.24.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Nov 2022 14:24:15 -0800 (PST) Date: Wed, 16 Nov 2022 22:24:11 +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-arch@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@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 , Shuah Khan , 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 , tabba@google.com, Michael Roth , mhocko@suse.com, Muchun Song , wei.w.wang@intel.com Subject: Re: [PATCH v9 5/8] KVM: Register/unregister the guest private memory regions Message-ID: References: <20221025151344.3784230-1-chao.p.peng@linux.intel.com> <20221025151344.3784230-6-chao.p.peng@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221025151344.3784230-6-chao.p.peng@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, Oct 25, 2022, Chao Peng wrote: > +static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size, > + bool is_private) > +{ > + gfn_t start, end; > + unsigned long i; > + void *entry; > + int idx; > + int r = 0; > + > + if (size == 0 || gpa + size < gpa) > + return -EINVAL; > + if (gpa & (PAGE_SIZE - 1) || size & (PAGE_SIZE - 1)) > + return -EINVAL; > + > + start = gpa >> PAGE_SHIFT; > + end = (gpa + size - 1 + PAGE_SIZE) >> PAGE_SHIFT; > + > + /* > + * Guest memory defaults to private, kvm->mem_attr_array only stores > + * shared memory. > + */ > + entry = is_private ? NULL : xa_mk_value(KVM_MEM_ATTR_SHARED); > + > + idx = srcu_read_lock(&kvm->srcu); > + KVM_MMU_LOCK(kvm); > + kvm_mmu_invalidate_begin(kvm, start, end); > + > + for (i = start; i < end; i++) { > + r = xa_err(xa_store(&kvm->mem_attr_array, i, entry, > + GFP_KERNEL_ACCOUNT)); > + if (r) > + goto err; > + } > + > + kvm_unmap_mem_range(kvm, start, end); > + > + goto ret; > +err: > + for (; i > start; i--) > + xa_erase(&kvm->mem_attr_array, i); I don't think deleting previous entries is correct. To unwind, the correct thing to do is restore the original values. E.g. if userspace space is mapping a large range as shared, and some of the previous entries were shared, deleting them would incorrectly "convert" those entries to private. Tracking the previous state likely isn't the best approach, e.g. it would require speculatively allocating extra memory for a rare condition that is likely going to lead to OOM anyways. Instead of trying to unwind, what about updating the ioctl() params such that retrying with the updated addr+size would Just Work? E.g. diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 55b07aae67cc..f1de592a1a06 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1015,15 +1015,12 @@ static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size, kvm_unmap_mem_range(kvm, start, end, attr); - goto ret; -err: - for (; i > start; i--) - xa_erase(&kvm->mem_attr_array, i); -ret: kvm_mmu_invalidate_end(kvm, start, end); KVM_MMU_UNLOCK(kvm); srcu_read_unlock(&kvm->srcu, idx); + + return r; } #endif /* CONFIG_KVM_GENERIC_PRIVATE_MEM */ @@ -4989,6 +4986,8 @@ static long kvm_vm_ioctl(struct file *filp, r = kvm_vm_ioctl_set_mem_attr(kvm, region.addr, region.size, set); + if (copy_to_user(argp, ®ion, sizeof(region)) && !r) + r = -EFAULT break; } #endif