linux-kernel - Re: [PATCH v3 3/5] x86/hyperv: Add an interface to do nested hypercalls

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Date:   Fri, 4 Nov 2022 16:19:48 +0530
From:   Anirudh Rayabharam <anrayabh@...ux.microsoft.com>
To:     Jinank Jain <jinankjain@...ux.microsoft.com>
Cc:     jinankjain@...rosoft.com, kys@...rosoft.com,
        haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        arnd@...db.de, peterz@...radead.org, jpoimboe@...nel.org,
        seanjc@...gle.com, kirill.shutemov@...ux.intel.com,
        ak@...ux.intel.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, mikelley@...rosoft.com
Subject: Re: [PATCH v3 3/5] x86/hyperv: Add an interface to do nested
 hypercalls

On Thu, Nov 03, 2022 at 01:04:05PM +0000, Jinank Jain wrote:
> 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@...ux.microsoft.com>
> ---
>  arch/x86/include/asm/hyperv-tlfs.h |  3 ++-
>  arch/x86/include/asm/mshyperv.h    | 42 +++++++++++++++++++++++++++---
>  include/asm-generic/hyperv-tlfs.h  |  1 +
>  3 files changed, 41 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 b0f16d06a0c5..32f6bed68e88 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -76,10 +76,16 @@ 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
>  	{
> @@ -107,10 +113,24 @@ 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
>  	{
> @@ -141,6 +161,20 @@ 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..3840958201cd 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_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)
> -- 
> 2.25.1

Reviewed-by: <anrayabh@...ux.microsoft.com>