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Thu, 25 Apr 2024 14:55:27 -0700 (PDT) Date: Thu, 25 Apr 2024 14:55:25 -0700 In-Reply-To: <20240425205245.aga3cyo5qa5xfnee@amd.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240421180122.1650812-1-michael.roth@amd.com> <20240421180122.1650812-4-michael.roth@amd.com> <20240425205245.aga3cyo5qa5xfnee@amd.com> Message-ID: Subject: Re: [PATCH v14 03/22] KVM: SEV: Add GHCB handling for Hypervisor Feature Support requests From: Sean Christopherson To: Michael Roth Cc: kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, jroedel@suse.de, thomas.lendacky@amd.com, hpa@zytor.com, ardb@kernel.org, pbonzini@redhat.com, vkuznets@redhat.com, jmattson@google.com, luto@kernel.org, dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com, peterz@infradead.org, srinivas.pandruvada@linux.intel.com, rientjes@google.com, dovmurik@linux.ibm.com, tobin@ibm.com, bp@alien8.de, vbabka@suse.cz, kirill@shutemov.name, ak@linux.intel.com, tony.luck@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, alpergun@google.com, jarkko@kernel.org, ashish.kalra@amd.com, nikunj.dadhania@amd.com, pankaj.gupta@amd.com, liam.merwick@oracle.com, Brijesh Singh Content-Type: text/plain; charset="us-ascii" On Thu, Apr 25, 2024, Michael Roth wrote: > On Wed, Apr 24, 2024 at 01:21:49PM -0700, Sean Christopherson wrote: > > On Sun, Apr 21, 2024, Michael Roth wrote: > > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c > > > index 6e31cb408dd8..1d2264e93afe 100644 > > > --- a/arch/x86/kvm/svm/sev.c > > > +++ b/arch/x86/kvm/svm/sev.c > > > @@ -33,9 +33,11 @@ > > > #include "cpuid.h" > > > #include "trace.h" > > > > > > -#define GHCB_VERSION_MAX 1ULL > > > +#define GHCB_VERSION_MAX 2ULL > > > #define GHCB_VERSION_MIN 1ULL > > > > This needs a userspace control. Being unable to limit the GHCB version advertised > > to the guest is going to break live migration of SEV-ES VMs, e.g. if a pool of > > hosts has some kernels running this flavor of KVM, and some hosts running an > > older KVM that doesn't support v2. > > > > The requirements for implementing the non-SNP aspects of the GHCB > version 2 protocol are fairly minimal, and KVM_SEV_INIT2 is already > migration incompatible with older kernels running KVM_SEV_ES_INIT (e.g. > migrate to newer host, shutdown, start -> measurement failure). There > are QEMU patches here that allow for controlling this via QEMU versioned > machine types to handle this [1] > > So I think it makes sense to go ahead move to GHCB version 2 as the base > version for all SEV-ES/SNP guests created via KVM_SEV_INIT2, and leave > KVM_SEV_ES_INIT restricted to GHCB version 1. Hmm, I like that. Dangle a carrot to get folks to switch to KVM_SEV_INIT2. > This could be done in a pretty self-contained way for SEV-ES by applying > the following patches from this series which are the version 2 protocol > interfaces also applicable to SEV-ES: > > KVM: SEV: Add GHCB handling for Hypervisor Feature Support requests > KVM: SEV: Add support to handle AP reset MSR protocol > KVM: SEV: Add support for GHCB-based termination requests > > And then applying the below patch on top to set GHCB version 1 or 2 > accordingly for SEV-ES. (and relocating the GHCB_VERSION_MAX bump to the > below patch as well, although it's not really used at that point so > could also just be dropped completely). > > Then in the future we can extend KVM_SEV_INIT2 to allow specifying > specific/newer versions of the GHCB protocol when that becomes needed. Any reason not to let userspace restrict the GHCB protocol from the get-go? It seems inevitable that KVM will need to support that at some point, we'd have a wee bit more confidence that we didn't botch the definition of KVM_SEV_INIT2 and end up with KVM_SEV_INIT3, and in the unlikely event some poor provider gets into a situation where guests are crashing because they don't handle v2 correctly, userspace can workaround the issue without need to extend KVM's uAPI. > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h > index 28140bc8af27..229cb630b540 100644 > --- a/arch/x86/kvm/svm/svm.h > +++ b/arch/x86/kvm/svm/svm.h > @@ -87,6 +87,7 @@ struct kvm_sev_info { > struct list_head regions_list; /* List of registered regions */ > u64 ap_jump_table; /* SEV-ES AP Jump Table address */ > u64 vmsa_features; > + u64 ghcb_version; /* Highest guest GHCB protocol version allowed */ This can/should be a u16, no? > struct kvm *enc_context_owner; /* Owner of copied encryption context */ > struct list_head mirror_vms; /* List of VMs mirroring */ > struct list_head mirror_entry; /* Use as a list entry of mirrors */