Re: [RFC PATCH v2 04/22] i386/kvm: handle Xen HVM cpuid leaves

[Paul Durrant <xadimgnik@gmail.com>]

On 09/12/2022 09:55, David Woodhouse wrote:
> From: Joao Martins <joao.m.martins@oracle.com>
> 
> Introduce support for emulating CPUID for Xen HVM guests. It doesn't make
> sense to advertise the KVM leaves to a Xen guest, so do it unconditionally
> when the xen-version machine property is set.
> 
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> [dwmw2: Obtain xen_version from machine property, make it automatic]
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
[snip]
> -    if (cpu->expose_kvm) {
> +    xen_version = kvm_arch_xen_version(MACHINE(qdev_get_machine()));
> +    if (xen_version) {
> +#ifdef CONFIG_XEN_EMU
> +        struct kvm_cpuid_entry2 *xen_max_leaf;
> +
> +        memcpy(signature, "XenVMMXenVMM", 12);
> +
> +        xen_max_leaf = c = &cpuid_data.entries[cpuid_i++];
> +        c->function = kvm_base + XEN_CPUID_SIGNATURE;
> +        c->eax = kvm_base + XEN_CPUID_TIME;
> +        c->ebx = signature[0];
> +        c->ecx = signature[1];
> +        c->edx = signature[2];
> +
> +        c = &cpuid_data.entries[cpuid_i++];
> +        c->function = kvm_base + XEN_CPUID_VENDOR;
> +        c->eax = xen_version;
> +        c->ebx = 0;
> +        c->ecx = 0;
> +        c->edx = 0;
> +
> +        c = &cpuid_data.entries[cpuid_i++];
> +        c->function = kvm_base + XEN_CPUID_HVM_MSR;
> +        /* Number of hypercall-transfer pages */
> +        c->eax = 1;
> +        /* Hypercall MSR base address */
> +        c->ebx = XEN_HYPERCALL_MSR;
> +        c->ecx = 0;
> +        c->edx = 0;
> +
> +        c = &cpuid_data.entries[cpuid_i++];
> +        c->function = kvm_base + XEN_CPUID_TIME;
> +        c->eax = ((!!tsc_is_stable_and_known(env) << 1) |
> +            (!!(env->features[FEAT_8000_0001_EDX] & CPUID_EXT2_RDTSCP) << 2));
> +        /* default=0 (emulate if necessary) */
> +        c->ebx = 0;
> +        /* guest tsc frequency */
> +        c->ecx = env->user_tsc_khz;
> +        /* guest tsc incarnation (migration count) */
> +        c->edx = 0;
> +
> +        c = &cpuid_data.entries[cpuid_i++];
> +        c->function = kvm_base + XEN_CPUID_HVM;
> +        xen_max_leaf->eax = kvm_base + XEN_CPUID_HVM;
> +        if (xen_version >= XEN_VERSION(4,5)) {
> +            c->function = kvm_base + XEN_CPUID_HVM;
> +
> +            if (cpu->xen_vapic) {
> +                c->eax |= XEN_HVM_CPUID_APIC_ACCESS_VIRT;
> +                c->eax |= XEN_HVM_CPUID_X2APIC_VIRT;
> +            }
> +
> +            c->eax |= XEN_HVM_CPUID_IOMMU_MAPPINGS;
> +
> +            if (xen_version >= XEN_VERSION(4,6)) {
> +                c->eax |= XEN_HVM_CPUID_VCPU_ID_PRESENT;
> +                c->ebx = cs->cpu_index;
> +            }
> +        }
> +
> +        kvm_base += 0x100;

Ok, this tells me that we are intending to handle Hyper-V enlightenments 
being simultaneously enabled... in which case that MSR above needs to 
move, along with the cpuid leaves. It should be 0x40000200 in this case.

   Paul