Re: [Qemu-devel] [QEMU PATCH v3 5/9] linux-headers: i386: Modify struct kvm_nested_state to have explicit fields for data

[Maran Wilson]

On 6/17/2019 10:56 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.
> * Add stub structs for AMD SVM.
>
> Signed-off-by: Liran Alon <address@hidden>
> ---
>   linux-headers/asm-x86/kvm.h | 41 +++++++++++++++++++++++++++----------
>   1 file changed, 30 insertions(+), 11 deletions(-)
>
> diff --git a/linux-headers/asm-x86/kvm.h b/linux-headers/asm-x86/kvm.h
> index 7a0e64ccd6ff..e655d108af19 100644
> --- a/linux-headers/asm-x86/kvm.h
> +++ b/linux-headers/asm-x86/kvm.h
> @@ -383,6 +383,9 @@ 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
> @@ -390,35 +393,51 @@ struct kvm_sync_regs {
>   #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[0x1000];
> +       __u8 shadow_vmcs12[0x1000];

I assume you will replace this magic 0x1000 value too, as discussed with 
respect to patch 7?

Thanks,
-Maran

> +};
> +
> +struct kvm_vmx_nested_state_hdr {
>         __u64 vmxon_pa;
> -       __u64 vmcs_pa;
> +       __u64 vmcs12_pa;
>   
>   	struct {
>                 __u16 flags;
>         } smm;
>   };
>   
> +struct kvm_svm_nested_state_data {
> +       /* TODO: Implement */
> +};
> +
> +struct kvm_svm_nested_state_hdr {
> +       /* TODO: Implement */
> +};
> +
>   /* 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;
> +               struct kvm_svm_nested_state_hdr svm;
>   
>   		/* 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];
> +               struct kvm_svm_nested_state_data svm[0];
> +       } data;
>   };
>   
>   #endif /* _ASM_X86_KVM_H */