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Date:   Fri, 4 Nov 2022 16:11:34 +0530
From:   Anirudh Rayabharam <anrayabh@linux.microsoft.com>
To:     Jinank Jain <jinankjain@linux.microsoft.com>
Cc:     jinankjain@microsoft.com, kys@microsoft.com,
        haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
        arnd@arndb.de, peterz@infradead.org, jpoimboe@kernel.org,
        seanjc@google.com, kirill.shutemov@linux.intel.com,
        ak@linux.intel.com, sathyanarayanan.kuppuswamy@linux.intel.com,
        linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arch@vger.kernel.org, mikelley@microsoft.com
Subject: Re: [PATCH v3 2/5] Drivers: hv: Setup synic registers in case of
 nested root partition
Message-ID: <Y2TsXjYaYEYTgQ/E@anrayabh-desk>
References: <cover.1667480257.git.jinankjain@linux.microsoft.com>
 <d8e549f443468f98ea701b27ffe47e4073d6d65d.1667480257.git.jinankjain@linux.microsoft.com>
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On Thu, Nov 03, 2022 at 01:04:04PM +0000, 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    | 24 ++++++++++++++++++++++++
>  drivers/hv/hv.c                    | 18 +++++++++++++-----
>  3 files changed, 48 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index d9a611565859..0319091e2019 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 3c39923e5969..b0f16d06a0c5 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -200,10 +200,31 @@ static inline bool hv_is_synic_reg(unsigned int reg)
>  	return false;
>  }
>  
> +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;
> +	}
> +}
> +
>  static inline u64 hv_get_register(unsigned int reg)
>  {
>  	u64 value;
>  
> +	if (hv_nested)
> +		reg = hv_get_nested_reg(reg);

With this change the nested root cannot read it's own SynIC MSRs using
this method. It will always read the SynIC MSRs corresponding to the
nesting hypervisor. Similar is the case with hv_set_register.

Will there never be a need for nested root to read/write it's own SynIC
MSRs? For e.g. to set up inter partition communication at the L2 level.

Anirudh.

> +
>  	if (hv_is_synic_reg(reg) && hv_isolation_type_snp())
>  		hv_ghcb_msr_read(reg, &value);
>  	else
> @@ -213,6 +234,9 @@ static inline u64 hv_get_register(unsigned int reg)
>  
>  static 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);
>  
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index 4d6480d57546..9e1eb50cc76f 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -147,7 +147,7 @@ int hv_synic_alloc(void)
>  		 * Synic message and event pages are allocated by paravisor.
>  		 * Skip these pages allocation here.
>  		 */
> -		if (!hv_isolation_type_snp()) {
> +		if (!hv_isolation_type_snp() && !hv_root_partition) {
>  			hv_cpu->synic_message_page =
>  				(void *)get_zeroed_page(GFP_ATOMIC);
>  			if (hv_cpu->synic_message_page == NULL) {
> @@ -188,8 +188,16 @@ void hv_synic_free(void)
>  		struct hv_per_cpu_context *hv_cpu
>  			= per_cpu_ptr(hv_context.cpu_context, cpu);
>  
> -		free_page((unsigned long)hv_cpu->synic_event_page);
> -		free_page((unsigned long)hv_cpu->synic_message_page);
> +		if (hv_root_partition) {
> +			if (hv_cpu->synic_event_page != NULL)
> +				memunmap(hv_cpu->synic_event_page);
> +
> +			if (hv_cpu->synic_message_page != NULL)
> +				memunmap(hv_cpu->synic_message_page);
> +		} else {
> +			free_page((unsigned long)hv_cpu->synic_event_page);
> +			free_page((unsigned long)hv_cpu->synic_message_page);
> +		}
>  		free_page((unsigned long)hv_cpu->post_msg_page);
>  	}
>  
> @@ -216,7 +224,7 @@ void hv_synic_enable_regs(unsigned int cpu)
>  	simp.as_uint64 = hv_get_register(HV_REGISTER_SIMP);
>  	simp.simp_enabled = 1;
>  
> -	if (hv_isolation_type_snp()) {
> +	if (hv_isolation_type_snp() || hv_root_partition) {
>  		hv_cpu->synic_message_page
>  			= memremap(simp.base_simp_gpa << HV_HYP_PAGE_SHIFT,
>  				   HV_HYP_PAGE_SIZE, MEMREMAP_WB);
> @@ -233,7 +241,7 @@ void hv_synic_enable_regs(unsigned int cpu)
>  	siefp.as_uint64 = hv_get_register(HV_REGISTER_SIEFP);
>  	siefp.siefp_enabled = 1;
>  
> -	if (hv_isolation_type_snp()) {
> +	if (hv_isolation_type_snp() || hv_root_partition) {
>  		hv_cpu->synic_event_page =
>  			memremap(siefp.base_siefp_gpa << HV_HYP_PAGE_SHIFT,
>  				 HV_HYP_PAGE_SIZE, MEMREMAP_WB);
> -- 
> 2.25.1