RE: [PATCH v2 3/5] hv: Add an interface to do nested hypercalls

["Michael Kelley (LINUX)" <mikelley@microsoft.com>]

From: Jinank Jain <jinankjain@linux.microsoft.com> Sent: Wednesday, November 2, 2022 9:36 AM
> 
> According to TLFS, in order to communicate to L0 hypervisor there needs
> to be an additional bit set in the control register. This communication
> is required to perform priviledged instructions which can only be
> performed by L0 hypervisor. An example of that could be setting up the
> VMBus infrastructure.
> 
> Signed-off-by: Jinank Jain <jinankjain@linux.microsoft.com>
> ---
>  arch/x86/include/asm/hyperv-tlfs.h |  3 ++-
>  arch/x86/include/asm/mshyperv.h    | 42 +++++++++++++++++++++++++++---
>  include/asm-generic/hyperv-tlfs.h  |  1 +
>  include/asm-generic/mshyperv.h     |  1 +
>  4 files changed, 42 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index 0319091e2019..fd066226f12b 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -380,7 +380,8 @@ struct hv_nested_enlightenments_control {
>  		__u32 reserved:31;
>  	} features;
>  	struct {
> -		__u32 reserved;
> +		__u32 inter_partition_comm:1;
> +		__u32 reserved:31;
>  	} hypercallControls;
>  } __packed;
> 
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 415289757428..451d8c3ab63b 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -74,10 +74,16 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void
> *output)
>  	return hv_status;
>  }
> 
> +/* Hypercall to the L0 hypervisor */
> +static inline u64 hv_do_nested_hypercall(u64 control, void *input, void *output)
> +{
> +	return hv_do_hypercall(control | HV_HYPERCALL_NESTED, input, output);
> +}
> +
>  /* Fast hypercall with 8 bytes of input and no output */
> -static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
> +static inline u64 _hv_do_fast_hypercall8(u64 control, u16 code, u64 input1)
>  {
> -	u64 hv_status, control = (u64)code | HV_HYPERCALL_FAST_BIT;
> +	u64 hv_status;
> 
>  #ifdef CONFIG_X86_64
>  	{
> @@ -105,10 +111,24 @@ static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
>  		return hv_status;
>  }
> 
> +static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
> +{
> +	u64 control = (u64)code | HV_HYPERCALL_FAST_BIT;
> +
> +	return _hv_do_fast_hypercall8(control, code, input1);
> +}
> +
> +static inline u64 hv_do_fast_nested_hypercall8(u16 code, u64 input1)
> +{
> +	u64 control = (u64)code | HV_HYPERCALL_FAST_BIT | HV_HYPERCALL_NESTED;
> +
> +	return _hv_do_fast_hypercall8(control, code, input1);
> +}
> +
>  /* Fast hypercall with 16 bytes of input */
> -static inline u64 hv_do_fast_hypercall16(u16 code, u64 input1, u64 input2)
> +static inline u64 _hv_do_fast_hypercall16(u64 control, u16 code, u64 input1, u64 input2)
>  {
> -	u64 hv_status, control = (u64)code | HV_HYPERCALL_FAST_BIT;
> +	u64 hv_status;
> 
>  #ifdef CONFIG_X86_64
>  	{
> @@ -139,6 +159,20 @@ static inline u64 hv_do_fast_hypercall16(u16 code, u64 input1, u64 input2)
>  	return hv_status;
>  }
> 
> +static inline u64 hv_do_fast_hypercall16(u16 code, u64 input1, u64 input2)
> +{
> +	u64 control = (u64)code | HV_HYPERCALL_FAST_BIT;
> +
> +	return _hv_do_fast_hypercall16(control, code, input1, input2);
> +}
> +
> +static inline u64 hv_do_fast_nested_hypercall16(u16 code, u64 input1, u64 input2)
> +{
> +	u64 control = (u64)code | HV_HYPERCALL_FAST_BIT | HV_HYPERCALL_NESTED;
> +
> +	return _hv_do_fast_hypercall16(control, code, input1, input2);
> +}
> +
>  extern struct hv_vp_assist_page **hv_vp_assist_page;
> 
>  static inline struct hv_vp_assist_page *hv_get_vp_assist_page(unsigned int cpu)
> diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
> index fdce7a4cfc6f..c67836dd8468 100644
> --- a/include/asm-generic/hyperv-tlfs.h
> +++ b/include/asm-generic/hyperv-tlfs.h
> @@ -185,6 +185,7 @@ enum HV_GENERIC_SET_FORMAT {
>  #define HV_HYPERCALL_VARHEAD_OFFSET	17
>  #define HV_HYPERCALL_VARHEAD_MASK	GENMASK_ULL(26, 17)
>  #define HV_HYPERCALL_RSVD0_MASK		GENMASK_ULL(31, 27)
> +#define HV_HYPERCALL_NESTED		BIT(31)

Since it is used with a bunch of other u64 values, the above should
probably be BIT_ULL(31).

>  #define HV_HYPERCALL_REP_COMP_OFFSET	32
>  #define HV_HYPERCALL_REP_COMP_1		BIT_ULL(32)
>  #define HV_HYPERCALL_REP_COMP_MASK	GENMASK_ULL(43, 32)
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index bfb9eb9d7215..a2524d96ce2d 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -53,6 +53,7 @@ extern void * __percpu *hyperv_pcpu_input_arg;
>  extern void * __percpu *hyperv_pcpu_output_arg;
> 
>  extern u64 hv_do_hypercall(u64 control, void *inputaddr, void *outputaddr);
> +extern u64 hv_do_nested_hypercall(u64 control, void *inputaddr, void *outputaddr);

Is this needed?  hv_do_nested_hypercall() is implemented as a static inline
function in the x86-specific version of mshyperv.h, so this seems duplicative.
But maybe I'm missing something ....

>  extern u64 hv_do_fast_hypercall8(u16 control, u64 input8);
>  extern bool hv_isolation_type_snp(void);
> 
> --
> 2.25.1