Re: [PATCH v2 12/15] mshv_vtl: Move VSM code page offset logic to x86 files

[Naman Jain <namjain@linux.microsoft.com>]

On 4/27/2026 11:10 AM, Michael Kelley wrote:
> From: Naman Jain <namjain@linux.microsoft.com> Sent: Thursday, April 23, 2026 5:42 AM
>>
>> The VSM code page offset register (HV_REGISTER_VSM_CODE_PAGE_OFFSETS)
>> is x86 specific, its value configures the static call used to return
>> to VTL0 via the hypercall page. Move the register read from the common
>> mshv_vtl_get_vsm_regs() into the x86 mshv_vtl_return_call_init(),
>> which is the sole consumer of the offset.
>>
>> Change mshv_vtl_return_call_init() from taking a u64 parameter
>> to taking no arguments, and rename mshv_vtl_get_vsm_regs() to
>> mshv_vtl_get_vsm_cap_reg() since it now only fetches
>> HV_REGISTER_VSM_CAPABILITIES.
>>
>> No functional change on x86. This prepares the common driver code for
>> ARM64 where VSM code page offsets do not apply.
>>
>> Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
>> ---
>>   arch/x86/hyperv/hv_vtl.c        | 19 +++++++++++++++++--
>>   arch/x86/include/asm/mshyperv.h |  4 ++--
>>   drivers/hv/mshv_vtl_main.c      | 24 +++++++++++++-----------
>>   3 files changed, 32 insertions(+), 15 deletions(-)
>>
>> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
>> index f3ffb6a7cb2d..7c10b34cf8a4 100644
>> --- a/arch/x86/hyperv/hv_vtl.c
>> +++ b/arch/x86/hyperv/hv_vtl.c
>> @@ -293,10 +293,25 @@ EXPORT_SYMBOL_GPL(hv_vtl_configure_reg_page);
>>
>>   DEFINE_STATIC_CALL_NULL(__mshv_vtl_return_hypercall, void (*)(void));
>>
>> -void mshv_vtl_return_call_init(u64 vtl_return_offset)
>> +int mshv_vtl_return_call_init(void)
>>   {
>> +	struct hv_register_assoc vsm_pg_offset_reg;
>> +	union hv_register_vsm_page_offsets offsets;
>> +	int ret;
>> +
>> +	vsm_pg_offset_reg.name = HV_REGISTER_VSM_CODE_PAGE_OFFSETS;
>> +
>> +	ret = hv_call_get_vp_registers(HV_VP_INDEX_SELF, HV_PARTITION_ID_SELF,
>> +				       1, input_vtl_zero, &vsm_pg_offset_reg);
>> +	if (ret)
>> +		return ret;
>> +
>> +	offsets.as_uint64 = vsm_pg_offset_reg.value.reg64;
>> +
>>   	static_call_update(__mshv_vtl_return_hypercall,
>> -			   (void *)((u8 *)hv_hypercall_pg + vtl_return_offset));
>> +			   (void *)((u8 *)hv_hypercall_pg + offsets.vtl_return_offset));
>> +
>> +	return 0;
>>   }
>>   EXPORT_SYMBOL(mshv_vtl_return_call_init);
>>
>> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
>> index b4d80c9a673a..b48f115c1292 100644
>> --- a/arch/x86/include/asm/mshyperv.h
>> +++ b/arch/x86/include/asm/mshyperv.h
>> @@ -286,14 +286,14 @@ struct mshv_vtl_cpu_context {
>>   #ifdef CONFIG_HYPERV_VTL_MODE
>>   void __init hv_vtl_init_platform(void);
>>   int __init hv_vtl_early_init(void);
>> -void mshv_vtl_return_call_init(u64 vtl_return_offset);
>> +int mshv_vtl_return_call_init(void);
>>   void mshv_vtl_return_hypercall(void);
>>   void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0);
>>   int hv_vtl_get_set_reg(struct hv_register_assoc *regs, bool set, bool shared);
>>   #else
>>   static inline void __init hv_vtl_init_platform(void) {}
>>   static inline int __init hv_vtl_early_init(void) { return 0; }
>> -static inline void mshv_vtl_return_call_init(u64 vtl_return_offset) {}
>> +static inline int mshv_vtl_return_call_init(void) { return 0; }
>>   static inline void mshv_vtl_return_hypercall(void) {}
>>   static inline void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0) {}
>>   #endif
>> diff --git a/drivers/hv/mshv_vtl_main.c b/drivers/hv/mshv_vtl_main.c
>> index 4c9ae65ad3e8..be498c9234fd 100644
>> --- a/drivers/hv/mshv_vtl_main.c
>> +++ b/drivers/hv/mshv_vtl_main.c
>> @@ -79,7 +79,6 @@ struct mshv_vtl {
>>   };
>>
>>   static struct mutex mshv_vtl_poll_file_lock;
>> -static union hv_register_vsm_page_offsets mshv_vsm_page_offsets;
>>   static union hv_register_vsm_capabilities mshv_vsm_capabilities;
>>
>>   static DEFINE_PER_CPU(struct mshv_vtl_poll_file, mshv_vtl_poll_file);
>> @@ -203,21 +202,19 @@ static void mshv_vtl_synic_enable_regs(unsigned int cpu)
>>   	/* VTL2 Host VSP SINT is (un)masked when the user mode requests that */
>>   }
>>
>> -static int mshv_vtl_get_vsm_regs(void)
>> +static int mshv_vtl_get_vsm_cap_reg(void)
>>   {
>> -	struct hv_register_assoc registers[2];
>> -	int ret, count = 2;
>> +	struct hv_register_assoc vsm_capability_reg;
>> +	int ret;
>>
>> -	registers[0].name = HV_REGISTER_VSM_CODE_PAGE_OFFSETS;
>> -	registers[1].name = HV_REGISTER_VSM_CAPABILITIES;
>> +	vsm_capability_reg.name = HV_REGISTER_VSM_CAPABILITIES;
>>
>>   	ret = hv_call_get_vp_registers(HV_VP_INDEX_SELF, HV_PARTITION_ID_SELF,
>> -				       count, input_vtl_zero, registers);
>> +				       1, input_vtl_zero, &vsm_capability_reg);
>>   	if (ret)
>>   		return ret;
>>
>> -	mshv_vsm_page_offsets.as_uint64 = registers[0].value.reg64;
>> -	mshv_vsm_capabilities.as_uint64 = registers[1].value.reg64;
>> +	mshv_vsm_capabilities.as_uint64 = vsm_capability_reg.value.reg64;
>>
>>   	return ret;
> 
> Nit: This could be just "return 0".

Acked.

> 
>>   }
>> @@ -1139,13 +1136,18 @@ static int __init mshv_vtl_init(void)
>>   	tasklet_init(&msg_dpc, mshv_vtl_sint_on_msg_dpc, 0);
>>   	init_waitqueue_head(&fd_wait_queue);
>>
>> -	if (mshv_vtl_get_vsm_regs()) {
>> +	if (mshv_vtl_get_vsm_cap_reg()) {
>>   		dev_emerg(dev, "Unable to get VSM capabilities !!\n");
> 
> Why is this failure an emergency message, while the other failures
> here in mshv_vtl_init() are just error messages? When there's lack
> of consistency, I always wonder if there is a reason ..... :-)

It might be because I didn’t pay enough attention to the old code :)
dev_err() should work just fine, I'll change it.


> 
>>   		ret = -ENODEV;
>>   		goto free_dev;
>>   	}
>>
>> -	mshv_vtl_return_call_init(mshv_vsm_page_offsets.vtl_return_offset);
>> +	ret = mshv_vtl_return_call_init();
>> +	if (ret) {
>> +		dev_err(dev, "mshv_vtl_return_call_init failed: %d\n", ret);
>> +		goto free_dev;
>> +	}
>> +
>>   	ret = hv_vtl_setup_synic();
>>   	if (ret)
>>   		goto free_dev;
>> --
>> 2.43.0
>>

Regards,
Naman