linux-kernel - Re: [PATCH] hyperv: Add missing field to hv_output_map_device

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Message-ID: <4ebde68b-1e39-4650-9f57-500843fa8aea@linux.microsoft.com>
Date: Fri, 15 Aug 2025 10:11:15 -0700
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: Wei Liu <wei.liu@...nel.org>, Michael Kelley <mhklinux@...look.com>
Cc: "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "kys@...rosoft.com" <kys@...rosoft.com>,
 "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
 "decui@...rosoft.com" <decui@...rosoft.com>
Subject: Re: [PATCH] hyperv: Add missing field to
 hv_output_map_device_interrupt

On 8/14/2025 2:16 PM, Wei Liu wrote:
> On Thu, Aug 14, 2025 at 06:57:22PM +0000, Michael Kelley wrote:
>> From: Nuno Das Neves <nunodasneves@...ux.microsoft.com> Sent: Wednesday, August 13, 2025 11:21 AM
>>>
>>> This field is unused, but the correct structure size is needed
>>> when computing the amount of space for the output argument to
>>> reside, so that it does not cross a page boundary.
>>>
>>> Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
>>> ---
>>>  include/hyperv/hvhdk_mini.h | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/include/hyperv/hvhdk_mini.h b/include/hyperv/hvhdk_mini.h
>>> index 42e7876455b5..858f6a3925b3 100644
>>> --- a/include/hyperv/hvhdk_mini.h
>>> +++ b/include/hyperv/hvhdk_mini.h
>>> @@ -301,6 +301,7 @@ struct hv_input_map_device_interrupt {
>>>  /* HV_OUTPUT_MAP_DEVICE_INTERRUPT */
>>>  struct hv_output_map_device_interrupt {
>>>  	struct hv_interrupt_entry interrupt_entry;
>>> +	u64 ext_status_deprecated[5];
>>
>> Your email identifying the problem said that without this
>> change, struct hv_output_map_device_interrupt is 0x10
>> bytes in size, which matches what I calculate from the definition.
>> This change adds 0x28 bytes, making the struct size now 0x38
>> bytes. But your other email said Hyper-V expects the size to be
>> 0x58 bytes. Is array size "5" correct, or is there some other
>> cause of the discrepancy?
>>

Ah, it looks like the *input* struct size (0x50) plus the size of
1 cpu bank is 0x58. The output struct size should indeed be 0x38.

I got them mixed up somehow when writing the email.
> 
> FWIW the array size 5 here is correct.
> 
> Wei
> 
>> Michael
>>
>>>  } __packed;
>>>
>>>  /* HV_INPUT_UNMAP_DEVICE_INTERRUPT */
>>> --
>>> 2.34.1
>>
>>