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Date: Fri, 10 Jun 2022 16:14:21 +0000 From: Sean Christopherson <seanjc@...gle.com> To: Chao Peng <chao.p.peng@...ux.intel.com> Cc: Andy Lutomirski <luto@...nel.org>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org, linux-doc@...r.kernel.org, qemu-devel@...gnu.org, Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>, Vitaly Kuznetsov <vkuznets@...hat.com>, Wanpeng Li <wanpengli@...cent.com>, Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>, Jeff Layton <jlayton@...nel.org>, "J . Bruce Fields" <bfields@...ldses.org>, Andrew Morton <akpm@...ux-foundation.org>, Mike Rapoport <rppt@...nel.org>, Steven Price <steven.price@....com>, "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>, Vlastimil Babka <vbabka@...e.cz>, Vishal Annapurve <vannapurve@...gle.com>, Yu Zhang <yu.c.zhang@...ux.intel.com>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, jun.nakajima@...el.com, dave.hansen@...el.com, ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com, ddutile@...hat.com, dhildenb@...hat.com, Quentin Perret <qperret@...gle.com>, Michael Roth <michael.roth@....com>, mhocko@...e.com Subject: Re: [PATCH v6 4/8] KVM: Extend the memslot to support fd-based private memory On Mon, May 30, 2022, Chao Peng wrote: > On Mon, May 23, 2022 at 03:22:32PM +0000, Sean Christopherson wrote: > > Actually, if the semantics are that userspace declares memory as private, then we > > can reuse KVM_MEMORY_ENCRYPT_REG_REGION and KVM_MEMORY_ENCRYPT_UNREG_REGION. It'd > > be a little gross because we'd need to slightly redefine the semantics for TDX, SNP, > > and software-protected VM types, e.g. the ioctls() currently require a pre-exisitng > > memslot. But I think it'd work... > > These existing ioctls looks good for TDX and probably SNP as well. For > softrware-protected VM types, it may not be enough. Maybe for the first > step we can reuse this for all hardware based solutions and invent new > interface when software-protected solution gets really supported. > > There is semantics difference for fd-based private memory. Current above > two ioctls() use userspace addreess(hva) while for fd-based it should be > fd+offset, and probably it's better to use gpa in this case. Then we > will need change existing semantics and break backward-compatibility. My thought was to keep the existing semantics for VMs with type==0, i.e. SEV and SEV-ES VMs. It's a bit gross, but the pinning behavior is a dead end for SNP and TDX, so it effectively needs to be deprecated anyways. I'm definitely not opposed to a new ioctl if Paolo or others think this is too awful, but burning an ioctl for this seems wasteful. Then generic KVM can do something like: case KVM_MEMORY_ENCRYPT_REG_REGION: case KVM_MEMORY_ENCRYPT_UNREG_REGION: struct kvm_enc_region region; if (!kvm_arch_vm_supports_private_memslots(kvm)) goto arch_vm_ioctl; r = -EFAULT; if (copy_from_user(®ion, argp, sizeof(region))) goto out; r = kvm_set_encrypted_region(ioctl, ®ion); break; default: arch_vm_ioctl: r = kvm_arch_vm_ioctl(filp, ioctl, arg); where common KVM provides __weak void kvm_arch_vm_supports_private_memslots(struct kvm *kvm) { return false; } and x86 overrides that to bool kvm_arch_vm_supports_private_memslots(struct kvm *kvm) { /* I can't remember what we decided on calling type '0' VMs. */ return !!kvm->vm_type; } and if someone ever wants to enable private memslot for SEV/SEV-ES guests we can always add a capability or even a new VM type. pKVM on arm can then obviously implement kvm_arch_vm_supports_private_memslots() to grab whatever identifies a pKVM VM.
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