Messages in this thread | | | Date | Fri, 20 Oct 2023 10:55:18 +1100 | Subject | Re: [PATCH v10 48/50] KVM: SEV: Provide support for SNP_GUEST_REQUEST NAE event | From | Alexey Kardashevskiy <> |
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On 20/10/23 01:57, Sean Christopherson wrote: > On Thu, Oct 19, 2023, Alexey Kardashevskiy wrote: >> >> On 19/10/23 00:48, Sean Christopherson wrote: >>> static int snp_handle_ext_guest_request(struct vcpu_svm *svm) >>> { >>> struct kvm_vcpu *vcpu = &svm->vcpu; >>> struct kvm *kvm = vcpu->kvm; >>> struct kvm_sev_info *sev; >>> unsigned long exitcode; >>> u64 data_gpa; >>> >>> if (!sev_snp_guest(vcpu->kvm)) { >>> ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SEV_RET_INVALID_GUEST); >>> return 1; >>> } >>> >>> data_gpa = vcpu->arch.regs[VCPU_REGS_RAX]; >>> if (!IS_ALIGNED(data_gpa, PAGE_SIZE)) { >>> ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SEV_RET_INVALID_ADDRESS); >>> return 1; >>> } >>> >>> vcpu->run->hypercall.nr = KVM_HC_SNP_GET_CERTS; >>> vcpu->run->hypercall.args[0] = data_gpa; >>> vcpu->run->hypercall.args[1] = vcpu->arch.regs[VCPU_REGS_RBX]; >>> vcpu->run->hypercall.flags = KVM_EXIT_HYPERCALL_LONG_MODE; >> >> btw why is it _LONG_MODE and not just _64? :) > > I'm pretty sure it got copied from Xen when KVM started adding supporting for > emulating Xen's hypercalls. I assume Xen PV actually has a need for identifying > long mode as opposed to just 64-bit mode, but KVM, not so much. > >>> vcpu->arch.complete_userspace_io = snp_complete_ext_guest_request; >>> return 0; >>> } >> >> This should work the KVM stored certs nicely but not for the global certs. >> Although I am not all convinced that global certs is all that valuable but I >> do not know the history of that, happened before I joined so I let others to >> comment on that. Thanks, > > Aren't the global certs provided by userspace too though? If all certs are > ultimately controlled by userspace, I don't see any reason to make the kernel a > middle-man.
The max blob size is 32KB or so and for 200 VMs it is: - 6.5MB, all in the userspace so swappable vs - 32KB but in the kernel so not swappable. Sure, a box capable of running 200 VMs must have plenty of RAM but still :) Plus, GHCB now has to go via the userspace before talking to the PSP which was not the case so far (though I cannot think of immediate implication right now).
-- Alexey
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