Re: [Qemu-devel] [QEMU PATCH v4 06/10] linux-headers: i386: Modify struct kvm_nested_state to have explicit fields for data

[Maran Wilson <maran.wilson@oracle.com>]

On 6/19/2019 9:21 AM, Liran Alon wrote:
> Improve the KVM_{GET,SET}_NESTED_STATE structs by detailing the format
> of VMX nested state data in a struct.
>
> In order to avoid changing the ioctl values of
> KVM_{GET,SET}_NESTED_STATE, there is a need to preserve
> sizeof(struct kvm_nested_state). This is done by defining the data
> struct as "data.vmx[0]". It was the most elegant way I found to
> preserve struct size while still keeping struct readable and easy to
> maintain. It does have a misfortunate side-effect that now it has to be
> accessed as "data.vmx[0]" rather than just "data.vmx".
>
> Because we are already modifying these structs, I also modified the
> following:
> * Define the "format" field values as macros.
> * Rename vmcs_pa to vmcs12_pa for better readability.
>
> Signed-off-by: Liran Alon <liran.alon@oracle.com>
> ---
>   linux-headers/asm-x86/kvm.h | 33 ++++++++++++++++++++++-----------
>   1 file changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/linux-headers/asm-x86/kvm.h b/linux-headers/asm-x86/kvm.h
> index 7a0e64ccd6ff..6e7dd792e448 100644
> --- a/linux-headers/asm-x86/kvm.h
> +++ b/linux-headers/asm-x86/kvm.h
> @@ -383,16 +383,26 @@ struct kvm_sync_regs {
>   #define KVM_X86_QUIRK_LAPIC_MMIO_HOLE	(1 << 2)
>   #define KVM_X86_QUIRK_OUT_7E_INC_RIP	(1 << 3)
>   
> +#define KVM_STATE_NESTED_FORMAT_VMX	0
> +#define KVM_STATE_NESTED_FORMAT_SVM	1
> +
>   #define KVM_STATE_NESTED_GUEST_MODE	0x00000001
>   #define KVM_STATE_NESTED_RUN_PENDING	0x00000002
>   #define KVM_STATE_NESTED_EVMCS		0x00000004
>   
> +#define KVM_STATE_NESTED_VMX_VMCS_SIZE	0x1000
> +
>   #define KVM_STATE_NESTED_SMM_GUEST_MODE	0x00000001
>   #define KVM_STATE_NESTED_SMM_VMXON	0x00000002
>   
> -struct kvm_vmx_nested_state {
> +struct kvm_vmx_nested_state_data {
> +	__u8 vmcs12[KVM_STATE_NESTED_VMX_VMCS_SIZE];
> +	__u8 shadow_vmcs12[KVM_STATE_NESTED_VMX_VMCS_SIZE];
> +};
> +
> +struct kvm_vmx_nested_state_hdr {
>   	__u64 vmxon_pa;
> -	__u64 vmcs_pa;
> +	__u64 vmcs12_pa;
>   
>   	struct {
>   		__u16 flags;
> @@ -401,24 +411,25 @@ struct kvm_vmx_nested_state {
>   
>   /* for KVM_CAP_NESTED_STATE */
>   struct kvm_nested_state {
> -	/* KVM_STATE_* flags */
>   	__u16 flags;
> -
> -	/* 0 for VMX, 1 for SVM.  */
>   	__u16 format;
> -
> -	/* 128 for SVM, 128 + VMCS size for VMX.  */
>   	__u32 size;
>   
>   	union {
> -		/* VMXON, VMCS */
> -		struct kvm_vmx_nested_state vmx;
> +		struct kvm_vmx_nested_state_hdr vmx;
>   
>   		/* Pad the header to 128 bytes.  */
>   		__u8 pad[120];
> -	};
> +	} hdr;
>   
> -	__u8 data[0];
> +	/*
> +	 * Define data region as 0 bytes to preserve backwards-compatability
> +	 * to old definition of kvm_nested_state in order to avoid changing
> +	 * KVM_{GET,PUT}_NESTED_STATE ioctl values.
> +	 */
> +	union {
> +		struct kvm_vmx_nested_state_data vmx[0];
> +	} data;
>   };
>   
>   #endif /* _ASM_X86_KVM_H */

Reviewed-by: Maran Wilson <maran.wilson@oracle.com>

Thanks,
-Maran