RE: [EXTERNAL] [PATCH V2 2/9] x86/hyperv: Set Virtual Trust Level in VMBus init message

[Saurabh Singh Sengar <ssengar@microsoft.com>]

> -----Original Message-----
> From: Tianyu Lan <ltykernel@gmail.com>
> Sent: Tuesday, June 27, 2023 8:53 AM
> To: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
> <haiyangz@microsoft.com>; wei.liu@kernel.org; Dexuan Cui
> <decui@microsoft.com>; tglx@linutronix.de; mingo@redhat.com;
> bp@alien8.de; dave.hansen@linux.intel.com; x86@kernel.org;
> hpa@zytor.com; daniel.lezcano@linaro.org; arnd@arndb.de; Michael Kelley
> (LINUX) <mikelley@microsoft.com>
> Cc: Tianyu Lan <Tianyu.Lan@microsoft.com>; linux-arch@vger.kernel.org;
> linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org;
> vkuznets@redhat.com
> Subject: [EXTERNAL] [PATCH V2 2/9] x86/hyperv: Set Virtual Trust Level in
> VMBus init message
> 
> From: Tianyu Lan <tiala@microsoft.com>
> 
> SEV-SNP guest provides vtl(Virtual Trust Level) and get it from Hyper-V hvcall
> via register hvcall HVCALL_ GET_VP_REGISTERS.
> 
> During initialization of VMBus, vtl needs to be set in the VMBus init message.
> 
> Signed-off-by: Tianyu Lan <tiala@microsoft.com>
> ---
>  arch/x86/hyperv/hv_init.c          | 36 ++++++++++++++++++++++++++++++
>  arch/x86/include/asm/hyperv-tlfs.h |  7 ++++++
>  drivers/hv/connection.c            |  1 +
>  include/asm-generic/mshyperv.h     |  1 +
>  include/linux/hyperv.h             |  4 ++--
>  5 files changed, 47 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c index
> 6c04b52f139b..1ba367a9686e 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -378,6 +378,40 @@ static void __init hv_get_partition_id(void)
>  	local_irq_restore(flags);
>  }
> 
> +static u8 __init get_vtl(void)
> +{
> +	u64 control = HV_HYPERCALL_REP_COMP_1 |
> HVCALL_GET_VP_REGISTERS;
> +	struct hv_get_vp_registers_input *input;
> +	struct hv_get_vp_registers_output *output;
> +	u64 vtl = 0;
> +	u64 ret;
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
> +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +	output = (struct hv_get_vp_registers_output *)input;
> +	if (!input) {
> +		local_irq_restore(flags);
> +		goto done;
> +	}
> +
> +	memset(input, 0, struct_size(input, element, 1));
> +	input->header.partitionid = HV_PARTITION_ID_SELF;
> +	input->header.vpindex = HV_VP_INDEX_SELF;
> +	input->header.inputvtl = 0;
> +	input->element[0].name0 = HV_X64_REGISTER_VSM_VP_STATUS;
> +
> +	ret = hv_do_hypercall(control, input, output);
> +	if (hv_result_success(ret))
> +		vtl = output->as64.low & HV_X64_VTL_MASK;
> +	else
> +		pr_err("Hyper-V: failed to get VTL! %lld", ret);

In case of error this function will return vtl=0, which can be the valid value of vtl.
I suggest we initialize vtl with -1 so and then check for its return.

This could be a good utility function which can be used for any Hyper-V VTL system, so think
of making it global ?

- Saurabh

> +	local_irq_restore(flags);
> +
> +done:
> +	return vtl;
> +}
> +
>  /*
>   * This function is to be invoked early in the boot sequence after the
>   * hypervisor has been detected.
> @@ -506,6 +540,8 @@ void __init hyperv_init(void)
>  	/* Query the VMs extended capability once, so that it can be cached.
> */
>  	hv_query_ext_cap(0);
> 
> +	/* Find the VTL */
> +	ms_hyperv.vtl = get_vtl();
>  	return;
> 
>  clean_guest_os_id:
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h
> b/arch/x86/include/asm/hyperv-tlfs.h
> index cea95dcd27c2..4bf0b315b0ce 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -301,6 +301,13 @@ enum hv_isolation_type {
>  #define HV_X64_MSR_TIME_REF_COUNT
> 	HV_REGISTER_TIME_REF_COUNT
>  #define HV_X64_MSR_REFERENCE_TSC
> 	HV_REGISTER_REFERENCE_TSC
> 
> +/*
> + * Registers are only accessible via HVCALL_GET_VP_REGISTERS hvcall and
> + * there is not associated MSR address.
> + */
> +#define	HV_X64_REGISTER_VSM_VP_STATUS	0x000D0003
> +#define	HV_X64_VTL_MASK			GENMASK(3, 0)
> +
>  /* Hyper-V memory host visibility */
>  enum hv_mem_host_visibility {
>  	VMBUS_PAGE_NOT_VISIBLE		= 0,
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c index
> 5978e9dbc286..02b54f85dc60 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -98,6 +98,7 @@ int vmbus_negotiate_version(struct
> vmbus_channel_msginfo *msginfo, u32 version)
>  	 */
>  	if (version >= VERSION_WIN10_V5) {
>  		msg->msg_sint = VMBUS_MESSAGE_SINT;
> +		msg->msg_vtl = ms_hyperv.vtl;
>  		vmbus_connection.msg_conn_id =
> VMBUS_MESSAGE_CONNECTION_ID_4;
>  	} else {
>  		msg->interrupt_page =
> virt_to_phys(vmbus_connection.int_page);
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-
> generic/mshyperv.h index 6b5c41f90398..f73a044ecaa7 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -54,6 +54,7 @@ struct ms_hyperv_info {
>  		};
>  	};
>  	u64 shared_gpa_boundary;
> +	u8 vtl;
>  };
>  extern struct ms_hyperv_info ms_hyperv;  extern bool hv_nested; diff --git
> a/include/linux/hyperv.h b/include/linux/hyperv.h index
> bfbc37ce223b..1f2bfec4abde 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -665,8 +665,8 @@ struct vmbus_channel_initiate_contact {
>  		u64 interrupt_page;
>  		struct {
>  			u8	msg_sint;
> -			u8	padding1[3];
> -			u32	padding2;
> +			u8	msg_vtl;
> +			u8	reserved[6];
>  		};
>  	};
>  	u64 monitor_page1;
> --
> 2.25.1