On Fri, May 19, 2023, Paolo Bonzini wrote: > On 5/3/23 18:08, Sean Christopherson wrote: > > Stop adjusting the guest's CPUID info for the allowed XFRM (a.k.a. XCR0) > > for SGX enclaves. Past me didn't understand the roles and responsibilities > > between userspace and KVM with respect to CPUID leafs, i.e. I thought I was > > being helpful by having KVM adjust the entries. > > > > This is clearly an ABI change, but QEMU does the right thing and AFAIK no > > other VMMs support SGX (yet), so I'm hopeful/confident that we can excise > > the ugly before userspace starts depending on the bad behavior. > > v2: > > - Collect reviews/testing. [Kai] > > - Require FP+SSE to always be set in XFRM, and exempt them from the XFRM > > vs. XCR0 check. [Kai] > > > > v1: https://lore.kernel.org/all/20230405005911.423699-1-seanjc@xxxxxxxxxx > > > > Sean Christopherson (3): > > KVM: VMX: Don't rely _only_ on CPUID to enforce XCR0 restrictions for > > ECREATE > > KVM: x86: Don't adjust guest's CPUID.0x12.1 (allowed SGX enclave XFRM) > > KVM: x86: Open code supported XCR0 calculation in > > kvm_vcpu_after_set_cpuid() > > > > arch/x86/kvm/cpuid.c | 43 ++++++++++-------------------------------- > > arch/x86/kvm/vmx/sgx.c | 11 +++++++++-- > > 2 files changed, 19 insertions(+), 35 deletions(-) > > > > > > base-commit: 5c291b93e5d665380dbecc6944973583f9565ee5 > > Queued, thanks. But why patch 3? I want to guard against future misuse of calculating the support XCR0 before the CPUID update is complete. I suppose I could have done this: static u64 guest_cpuid_supported_xcr0(struct kvm_vcpu *vcpu) { struct kvm_cpuid_entry2 *best; best = kvm_find_cpuid_entry_index(vcpu, 0xd, 0); if (!best) return 0; return (best->eax | ((u64)best->edx << 32)) & kvm_caps.supported_xcr0; } but I don't really see the point since there should only ever be one caller, e.g. unlike cpuid_query_maxphyaddr() which needs a non-zero default. > Small functions are nice and remove the need to remember what is in EDX:EAX > of CPUID[0xD,0]. Hmm, yes and no. Specifically, I dislike single-use helpers that bury unintuitive details in the helper, e.g. in this case, filtering the raw iguest CPUID with KVM's kvm_caps.supported_xcr0. Communicating that in the name of the function so that they're are no surprises is often more difficult than just open coding things.
