linux-kernel - Re: [PATCH 02/29] KVM: API definitions for plane userspace exit

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Message-ID: <aD-O6EBMqPwLzgd_@google.com>
Date: Tue, 3 Jun 2025 17:10:16 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, roy.hopkins@...e.com, 
	thomas.lendacky@....com, ashish.kalra@....com, michael.roth@....com, 
	jroedel@...e.de, nsaenz@...zon.com, anelkz@...zon.de, 
	James.Bottomley@...senpartnership.com
Subject: Re: [PATCH 02/29] KVM: API definitions for plane userspace exit

On Tue, Apr 01, 2025, Paolo Bonzini wrote:
> Copy over the uapi definitions from the Documentation/ directory.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  include/uapi/linux/kvm.h | 25 +++++++++++++++++++++++--
>  1 file changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 1e0a511c43d0..b0cca93ebcb3 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -135,6 +135,16 @@ struct kvm_xen_exit {
>  	} u;
>  };
>  
> +struct kvm_plane_event_exit {
> +#define KVM_PLANE_EVENT_INTERRUPT    1
> +	__u16 cause;
> +	__u16 pending_event_planes;
> +	__u16 target;
> +	__u16 padding;
> +	__u32 flags;
> +	__u64 extra[8];
> +};
> +
>  struct kvm_tdx_exit {
>  #define KVM_EXIT_TDX_VMCALL     1
>          __u32 type;
> @@ -262,7 +272,8 @@ struct kvm_tdx_exit {
>  #define KVM_EXIT_NOTIFY           37
>  #define KVM_EXIT_LOONGARCH_IOCSR  38
>  #define KVM_EXIT_MEMORY_FAULT     39
> -#define KVM_EXIT_TDX              40
> +#define KVM_EXIT_PLANE_EVENT      40
> +#define KVM_EXIT_TDX              41
>  
>  /* For KVM_EXIT_INTERNAL_ERROR */
>  /* Emulate instruction failed. */
> @@ -295,7 +306,13 @@ struct kvm_run {
>  	/* in */
>  	__u8 request_interrupt_window;
>  	__u8 HINT_UNSAFE_IN_KVM(immediate_exit);
> -	__u8 padding1[6];
> +
> +	/* in/out */
> +	__u8 plane;

We should add padding before or after "plane"; there's a 1-byte hole here that's
hard to spot at first glance (ran pahole just to verify my eyeballs):

  struct kvm_run {
	__u8                       request_interrupt_window; /*     0     1 */
	__u8                       immediate_exit__unsafe; /*     1     1 */
	__u8                       plane;                /*     2     1 */

	/* XXX 1 byte hole, try to pack */

	__u16                      suspended_planes;     /*     4     2 */
	__u16                      req_exit_planes;      /*     6     2 */
  }

Probably pad before, so that "plane" is just before the xxx_planes fields?