Re: [PATCH v4 2/5] Drivers: hv: Setup synic registers in case of nested root partition

[Nuno Das Neves <nunodasneves@linux.microsoft.com>]

On 11/16/2022 7:27 PM, Jinank Jain wrote:
> Child partitions are free to allocate SynIC message and event page but in
> case of root partition it must use the pages allocated by Microsoft
> Hypervisor (MSHV). Base address for these pages can be found using
> synthetic MSRs exposed by MSHV. There is a slight difference in those MSRs
> for nested vs non-nested root partition.
> 
> Signed-off-by: Jinank Jain <jinankjain@linux.microsoft.com>
> ---
>  arch/x86/include/asm/hyperv-tlfs.h | 11 +++++++
>  arch/x86/include/asm/mshyperv.h    | 26 ++--------------
>  arch/x86/kernel/cpu/mshyperv.c     | 49 ++++++++++++++++++++++++++++++
>  drivers/hv/hv.c                    | 18 ++++++++---
>  4 files changed, 75 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index 58c03d18c235..b5019becb618 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -225,6 +225,17 @@ enum hv_isolation_type {
>  #define HV_REGISTER_SINT14			0x4000009E
>  #define HV_REGISTER_SINT15			0x4000009F
>  
> +/*
> + * Define synthetic interrupt controller model specific registers for
> + * nested hypervisor.
> + */
> +#define HV_REGISTER_NESTED_SCONTROL            0x40001080
> +#define HV_REGISTER_NESTED_SVERSION            0x40001081
> +#define HV_REGISTER_NESTED_SIEFP               0x40001082
> +#define HV_REGISTER_NESTED_SIMP                0x40001083
> +#define HV_REGISTER_NESTED_EOM                 0x40001084
> +#define HV_REGISTER_NESTED_SINT0               0x40001090
> +
>  /*
>   * Synthetic Timer MSRs. Four timers per vcpu.
>   */
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 61f0c206bff0..326d699b30d5 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -198,30 +198,8 @@ static inline bool hv_is_synic_reg(unsigned int reg)
>  	return false;
>  }
>  
> -static inline u64 hv_get_register(unsigned int reg)
> -{
> -	u64 value;
> -
> -	if (hv_is_synic_reg(reg) && hv_isolation_type_snp())
> -		hv_ghcb_msr_read(reg, &value);
> -	else
> -		rdmsrl(reg, value);
> -	return value;
> -}
> -
> -static inline void hv_set_register(unsigned int reg, u64 value)
> -{
> -	if (hv_is_synic_reg(reg) && hv_isolation_type_snp()) {
> -		hv_ghcb_msr_write(reg, value);
> -
> -		/* Write proxy bit via wrmsl instruction */
> -		if (reg >= HV_REGISTER_SINT0 &&
> -		    reg <= HV_REGISTER_SINT15)
> -			wrmsrl(reg, value | 1 << 20);
> -	} else {
> -		wrmsrl(reg, value);
> -	}
> -}
> +u64 hv_get_register(unsigned int reg);
> +void hv_set_register(unsigned int reg, u64 value);
>  
>  #else /* CONFIG_HYPERV */
>  static inline void hyperv_init(void) {}
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 9a4204139490..3e6711a6af6b 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -41,6 +41,55 @@ bool hv_root_partition;
>  bool hv_nested;
>  struct ms_hyperv_info ms_hyperv;
>  
> +static inline unsigned int hv_get_nested_reg(unsigned int reg)
> +{
> +	switch (reg) {
> +	case HV_REGISTER_SIMP:
> +		return HV_REGISTER_NESTED_SIMP;
> +	case HV_REGISTER_NESTED_SIEFP:
> +		return HV_REGISTER_SIEFP;
> +	case HV_REGISTER_SCONTROL:
> +		return HV_REGISTER_NESTED_SCONTROL;
> +	case HV_REGISTER_SINT0:
> +		return HV_REGISTER_NESTED_SINT0;
> +	case HV_REGISTER_EOM:
> +		return HV_REGISTER_NESTED_EOM;
> +	default:
> +		return reg;
> +	}
> +}
> +
> +inline u64 hv_get_register(unsigned int reg)
> +{
> +	u64 value;
> +
> +	if (hv_nested)
> +		reg = hv_get_nested_reg(reg);
> +
> +	if (hv_is_synic_reg(reg) && hv_isolation_type_snp())
> +		hv_ghcb_msr_read(reg, &value);
> +	else
> +		rdmsrl(reg, value);
> +	return value;
> +}
> +
> +inline void hv_set_register(unsigned int reg, u64 value)
> +{
> +	if (hv_nested)
> +		reg = hv_get_nested_reg(reg);
> +
> +	if (hv_is_synic_reg(reg) && hv_isolation_type_snp()) {
> +		hv_ghcb_msr_write(reg, value);
> +
> +		/* Write proxy bit via wrmsl instruction */
> +		if (reg >= HV_REGISTER_SINT0 &&
> +		    reg <= HV_REGISTER_SINT15)
> +			wrmsrl(reg, value | 1 << 20);
> +	} else {
> +		wrmsrl(reg, value);
> +	}
> +}

This approach has a problem, in that it removes the interface for getting and
setting the non-nested SIMP etc...
We will need to use the non-nested SIMP for getting intercepts in the root
partition from the L1 hypervisor.

Nuno