Re: [PATCH v2 1/3] hyperv: Convert hypercall statuses to linux error codes

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

On 2/20/2025 11:03 AM, Michael Kelley wrote:
> From: Nuno Das Neves <nunodasneves@linux.microsoft.com> Sent: Thursday, February 20, 2025 10:33 AM
>>
>> Return linux-friendly error codes from hypercall helper functions,
>> which allows them to be used more flexibly.
>>
>> Introduce hv_result_to_errno() for this purpose, which also handles
>> the special value U64_MAX returned from hv_do_hypercall().
>>
>> Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
>> ---
>>  drivers/hv/hv_common.c         | 34 ++++++++++++++++++++++++++++++++++
>>  drivers/hv/hv_proc.c           |  6 +++---
>>  include/asm-generic/mshyperv.h |  1 +
>>  3 files changed, 38 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
>> index ee3083937b4f..2120aead98d9 100644
>> --- a/drivers/hv/hv_common.c
>> +++ b/drivers/hv/hv_common.c
>> @@ -683,3 +683,37 @@ u64 __weak hv_tdx_hypercall(u64 control, u64 param1, u64 param2)
>>  	return HV_STATUS_INVALID_PARAMETER;
>>  }
>>  EXPORT_SYMBOL_GPL(hv_tdx_hypercall);
>> +
>> +/* Convert a hypercall result into a linux-friendly error code. */
>> +int hv_result_to_errno(u64 status)
>> +{
>> +	/* hv_do_hypercall() may return U64_MAX, hypercalls aren't possible */
>> +	if (unlikely(status == U64_MAX))
>> +		return -EOPNOTSUPP;
>> +	/*
>> +	 * A failed hypercall is usually only recoverable (or loggable) near
>> +	 * the call site where the HV_STATUS_* code is known. So the errno
>> +	 * it gets converted to is not too useful further up the stack.
>> +	 * Provice a few mappings that could be useful, and revert to -EIO
>> +	 * as a fallback.
>> +	 */
>> +	switch (hv_result(status)) {
>> +	case HV_STATUS_SUCCESS:
>> +		return 0;
>> +	case HV_STATUS_INVALID_HYPERCALL_CODE:
>> +	case HV_STATUS_INVALID_HYPERCALL_INPUT:
>> +	case HV_STATUS_INVALID_PARAMETER:
>> +	case HV_STATUS_INVALID_PARTITION_ID:
>> +	case HV_STATUS_INVALID_VP_INDEX:
>> +	case HV_STATUS_INVALID_PORT_ID:
>> +	case HV_STATUS_INVALID_CONNECTION_ID:
>> +	case HV_STATUS_INVALID_LP_INDEX:
>> +	case HV_STATUS_INVALID_REGISTER_VALUE:
>> +		return -EINVAL;
>> +	case HV_STATUS_INSUFFICIENT_MEMORY:
>> +		return -ENOMEM;
>> +	default:
>> +		break;
>> +	}
>> +	return -EIO;
>> +}
>> diff --git a/drivers/hv/hv_proc.c b/drivers/hv/hv_proc.c
>> index 3e410489f480..72b09f1cfa3e 100644
>> --- a/drivers/hv/hv_proc.c
>> +++ b/drivers/hv/hv_proc.c
>> @@ -88,7 +88,7 @@ int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages)
>>  	local_irq_restore(flags);
>>  	if (!hv_result_success(status)) {
>>  		pr_err("Failed to deposit pages: %lld\n", status);
>> -		ret = hv_result(status);
>> +		ret = hv_result_to_errno(status);
>>  		goto err_free_allocations;
>>  	}
>>
>> @@ -139,7 +139,7 @@ int hv_call_add_logical_proc(int node, u32 lp_index, u32 apic_id)
>>  			if (!hv_result_success(status)) {
>>  				pr_err("%s: cpu %u apic ID %u, %lld\n", __func__,
>>  				       lp_index, apic_id, status);
>> -				ret = hv_result(status);
>> +				ret = hv_result_to_errno(status);
>>  			}
>>  			break;
>>  		}
>> @@ -181,7 +181,7 @@ int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags)
>>  			if (!hv_result_success(status)) {
>>  				pr_err("%s: vcpu %u, lp %u, %lld\n", __func__,
>>  				       vp_index, flags, status);
>> -				ret = hv_result(status);
>> +				ret = hv_result_to_errno(status);
>>  			}
>>  			break;
>>  		}
> 
> In hv_call_add_logical_proc() and hv_call_create_vp(), local variable "ret" is
> defined and initialized to HV_STATUS_SUCCESS.  Since "ret" now contains an
> errno value instead of a hypercall status, it should be initialized to zero.  (Yes,
> HV_STATUS_SUCCESS is defined as 0, but it's now the wrong abstraction.)
> 
Great point, I'll post a v3 to fix it.

> With that fixed,
> 
> Reviewed-by: Michael Kelley <mhklinux@outlook.com>
> 
>> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
>> index 7adc10a4fa3e..3f115e2bcdaa 100644
>> --- a/include/asm-generic/mshyperv.h
>> +++ b/include/asm-generic/mshyperv.h
>> @@ -297,6 +297,7 @@ static inline int cpumask_to_vpset_skip(struct hv_vpset *vpset,
>>  	return __cpumask_to_vpset(vpset, cpus, func);
>>  }
>>
>> +int hv_result_to_errno(u64 status);
>>  void hyperv_report_panic(struct pt_regs *regs, long err, bool in_die);
>>  bool hv_is_hyperv_initialized(void);
>>  bool hv_is_hibernation_supported(void);
>> --
>> 2.34.1