On Fri, Jun 21, 2024, Michael Roth wrote:
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index ecfa25b505e7..2eea9828d9aa 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -7122,6 +7122,97 @@ Please note that the kernel is allowed to use the kvm_run structure as the
> primary storage for certain register types. Therefore, the kernel may use the
> values in kvm_run even if the corresponding bit in kvm_dirty_regs is not set.
>
> +::
> +
> + /* KVM_EXIT_COCO */
> + struct kvm_exit_coco {
> + #define KVM_EXIT_COCO_REQ_CERTS 0
> + #define KVM_EXIT_COCO_MAX 1
> + __u8 nr;
> + __u8 pad0[7];
> + union {
> + struct {
> + __u64 gfn;
> + __u32 npages;
> + #define KVM_EXIT_COCO_REQ_CERTS_ERR_INVALID_LEN 1
> + #define KVM_EXIT_COCO_REQ_CERTS_ERR_GENERIC (1 << 31)
Unless I'm mistaken, these error codes are defined by the GHCB, which means the
values matter, i.e. aren't arbitrary KVM-defined values.
I forget exactly what we discussed in PUCK, but for the error codes, I think KVM
should either define it's own values that are completely disconnected from any
"harware" spec, or KVM should very explicitly #define all hardware values and have
the semantics of "ret" be vendor specific. A hybrid approach doesn't really work,
e.g. KVM_EXIT_COCO_REQ_CERTS_ERR_GENERIC isn't used anywhere and and looks quite odd.
My vote is for vendor specific error codes, because unlike having a common user
exit reason+struct, I don't think arch-neutral error codes will minimize KVM's ABI,
I think it'll do the exact opposite. The only thing we need to require is that
'0' == success.
E.g. I think we can end up with something like:
static int snp_complete_req_certs(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
struct vmcb_control_area *control = &svm->vmcb->control;
if (vcpu->run->coco.req_certs.ret)
if (vcpu->run->coco.req_certs.ret == SNP_GUEST_VMM_ERR_INVALID_LEN)
vcpu->arch.regs[VCPU_REGS_RBX] = vcpu->run->coco.req_certs.npages;
ghcb_set_sw_exit_info_2(svm->sev_es.ghcb,
SNP_GUEST_ERR(vcpu->run->coco.req_certs.ret, 0));
return 1;
}
return snp_handle_guest_req(svm, control->exit_info_1, control->exit_info_2);
}
> + __u32 ret;
> + } req_certs;
> + };
