Re: [PATCH v2 01/13] KVM: x86: Redefine 'longmode' as a flag for KVM_EXIT_HYPERCALL

[Sean Christopherson <seanjc@google.com>]

On Thu, Mar 30, 2023, Oliver Upton wrote:
> The 'longmode' field is a bit annoying as it blows an entire __u32 to
> represent a boolean value. Since other architectures are looking to add
> support for KVM_EXIT_HYPERCALL, now is probably a good time to clean it
> up.
> 
> Redefine the field (and the remaining padding) as a set of flags.
> Preserve the existing ABI by using bit 0 to indicate if the guest was in
> long mode and requiring that the remaining 31 bits must be zero.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> ---

Acked-by: Sean Christopherson <seanjc@google.com>

>  Documentation/virt/kvm/api.rst  | 3 +--
>  arch/x86/include/asm/kvm_host.h | 7 +++++++
>  arch/x86/include/uapi/asm/kvm.h | 3 +++
>  arch/x86/kvm/x86.c              | 6 +++++-
>  include/uapi/linux/kvm.h        | 9 +++++++--
>  5 files changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 62de0768d6aa..9b01e3d0e757 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6218,8 +6218,7 @@ to the byte array.
>  			__u64 nr;
>  			__u64 args[6];
>  			__u64 ret;
> -			__u32 longmode;
> -			__u32 pad;
> +			__u64 flags;
>  		} hypercall;
>  
>  Unused.  This was once used for 'hypercall to userspace'.  To implement

Note to self, this needs to be updated as "hypercall" is longer unused.