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[34.168.104.7]) by smtp.gmail.com with ESMTPSA id x12-20020a62860c000000b0056281da3bcbsm1297475pfd.149.2022.11.03.16.04.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Nov 2022 16:04:57 -0700 (PDT) Date: Thu, 3 Nov 2022 23:04:53 +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: > @@ -4708,6 +4802,24 @@ static long kvm_vm_ioctl(struct file *filp, > r = kvm_vm_ioctl_set_memory_region(kvm, &mem); > break; > } > +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM > + case KVM_MEMORY_ENCRYPT_REG_REGION: > + case KVM_MEMORY_ENCRYPT_UNREG_REGION: { I'm having second thoughts about usurping KVM_MEMORY_ENCRYPT_(UN)REG_REGION. Aside from the fact that restricted/protected memory may not be encrypted, there are other potential use cases for per-page memory attributes[*], e.g. to make memory read-only (or no-exec, or exec-only, etc...) without having to modify memslots. Any paravirt use case where the attributes of a page are effectively dictated by the guest is going to run into the exact same performance problems with memslots, which isn't suprising in hindsight since shared vs. private is really just an attribute, albeit with extra special semantics. And if we go with a brand new ioctl(), maybe someday in the very distant future we can deprecate and delete KVM_MEMORY_ENCRYPT_(UN)REG_REGION. Switching to a new ioctl() should be a minor change, i.e. shouldn't throw too big of a wrench into things. Something like: KVM_SET_MEMORY_ATTRIBUTES struct kvm_memory_attributes { __u64 address; __u64 size; __u64 flags; } [*] https://lore.kernel.org/all/Y1a1i9vbJ%2FpVmV9r@google.com > + struct kvm_enc_region region; > + bool set = ioctl == KVM_MEMORY_ENCRYPT_REG_REGION; > + > + if (!kvm_arch_has_private_mem(kvm)) > + goto arch_vm_ioctl; > + > + r = -EFAULT; > + if (copy_from_user(®ion, argp, sizeof(region))) > + goto out; > + > + r = kvm_vm_ioctl_set_mem_attr(kvm, region.addr, > + region.size, set); > + break; > + } > +#endif