Re: [PATCH 04/10] KVM: SEV: publish supported VMSA features

[Michael Roth <michael.roth@amd.com>]

On Fri, Feb 09, 2024 at 01:37:36PM -0500, Paolo Bonzini wrote:
> Compute the set of features to be stored in the VMSA when KVM is
> initialized; move it from there into kvm_sev_info when SEV is initialized,
> and then into the initial VMSA.
> 
> The new variable can then be used to return the set of supported features
> to userspace, via the KVM_GET_DEVICE_ATTR ioctl.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  .../virt/kvm/x86/amd-memory-encryption.rst    | 12 ++++++++++
>  arch/x86/include/uapi/asm/kvm.h               |  1 +
>  arch/x86/kvm/svm/sev.c                        | 22 +++++++++++++++++--
>  arch/x86/kvm/svm/svm.c                        |  1 +
>  arch/x86/kvm/svm/svm.h                        |  1 +
>  5 files changed, 35 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/virt/kvm/x86/amd-memory-encryption.rst b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> index 37c5c37f4f6e..5ed11bc16b96 100644
> --- a/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> +++ b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> @@ -424,6 +424,18 @@ issued by the hypervisor to make the guest ready for execution.
>  
>  Returns: 0 on success, -negative on error
>  
> +Device attribute API
> +====================
> +
> +Attributes of the SEV implementation can be retrieved through the
> +``KVM_HAS_DEVICE_ATTR`` and ``KVM_GET_DEVICE_ATTR`` ioctls on the ``/dev/kvm``
> +device node.
> +
> +Currently only one attribute is implemented:
> +
> +* group 0, attribute ``KVM_X86_SEV_VMSA_FEATURES``: return the set of all
> +  bits that are accepted in the ``vmsa_features`` of ``KVM_SEV_INIT2``.
> +
>  Firmware Management
>  ===================
>  
> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> index b305daff056e..cccaa5ff6d01 100644
> --- a/arch/x86/include/uapi/asm/kvm.h
> +++ b/arch/x86/include/uapi/asm/kvm.h
> @@ -459,6 +459,7 @@ struct kvm_sync_regs {
>  
>  /* attributes for system fd (group 0) */
>  #define KVM_X86_XCOMP_GUEST_SUPP	0
> +#define KVM_X86_SEV_VMSA_FEATURES	1
>  
>  struct kvm_vmx_nested_state_data {
>  	__u8 vmcs12[KVM_STATE_NESTED_VMX_VMCS_SIZE];
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index f760106c31f8..2e558f7538c2 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -65,6 +65,7 @@ module_param_named(debug_swap, sev_es_debug_swap_enabled, bool, 0444);
>  #define sev_es_debug_swap_enabled false
>  #endif /* CONFIG_KVM_AMD_SEV */
>  
> +static u64 sev_supported_vmsa_features;
>  static u8 sev_enc_bit;
>  static DECLARE_RWSEM(sev_deactivate_lock);
>  static DEFINE_MUTEX(sev_bitmap_lock);

...

> @@ -2276,6 +2290,10 @@ void __init sev_hardware_setup(void)
>  	if (!sev_es_enabled || !cpu_feature_enabled(X86_FEATURE_DEBUG_SWAP) ||
>  	    !cpu_feature_enabled(X86_FEATURE_NO_NESTED_DATA_BP))
>  		sev_es_debug_swap_enabled = false;
> +
> +	sev_supported_vmsa_features = 0;

This ^ seems unecessary. Otherwise:

Reviewed-by: Michael Roth <michael.roth@amd.com>

> +	if (sev_es_debug_swap_enabled)
> +		sev_supported_vmsa_features |= SVM_SEV_FEAT_DEBUG_SWAP;
>  #endif
>  }