linux-kernel - Re: [PATCH v5 03/10] arm64/hyperv: Add some missing functions to arm64

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Message-ID: <9cd97b0e-dfd3-4923-961e-00ba09eb6cef@linux.microsoft.com>
Date: Fri, 7 Mar 2025 13:55:22 -0800
From: Easwar Hariharan <eahariha@...ux.microsoft.com>
To: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
Cc: Michael Kelley <mhklinux@...look.com>, eahariha@...ux.microsoft.com,
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Subject: Re: [PATCH v5 03/10] arm64/hyperv: Add some missing functions to
 arm64

On 3/7/2025 1:36 PM, Nuno Das Neves wrote:
> On 3/6/2025 11:05 AM, Michael Kelley wrote:
>> From: Nuno Das Neves <nunodasneves@...ux.microsoft.com> Sent: Thursday, February 27, 2025 4:21 PM
>>>
>>> On 2/26/2025 9:56 PM, Easwar Hariharan wrote:
>>>> On 2/26/2025 3:07 PM, Nuno Das Neves wrote:
>>>>> These non-nested msr and fast hypercall functions are present in x86,
>>>>> but they must be available in both architetures for the root partition
>>>>
>>>> nit: *architectures*
>>>>
>>>>
>>> Thanks!
>>>
>>>>> driver code.
>>>>>
>>>>> Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
>>>>> ---
>>>>>  arch/arm64/hyperv/hv_core.c       | 17 +++++++++++++++++
>>>>>  arch/arm64/include/asm/mshyperv.h | 12 ++++++++++++
>>>>>  include/asm-generic/mshyperv.h    |  2 ++
>>>>>  3 files changed, 31 insertions(+)
>>>>>
>>>>> diff --git a/arch/arm64/hyperv/hv_core.c b/arch/arm64/hyperv/hv_core.c
>>>>> index 69004f619c57..e33a9e3c366a 100644
>>>>> --- a/arch/arm64/hyperv/hv_core.c
>>>>> +++ b/arch/arm64/hyperv/hv_core.c
>>>>> @@ -53,6 +53,23 @@ u64 hv_do_fast_hypercall8(u16 code, u64 input)
>>>>>  }
>>>>>  EXPORT_SYMBOL_GPL(hv_do_fast_hypercall8);
>>>>>
>>>>> +/*
>>>>> + * hv_do_fast_hypercall16 -- Invoke the specified hypercall
>>>>> + * with arguments in registers instead of physical memory.
>>>>> + * Avoids the overhead of virt_to_phys for simple hypercalls.
>>>>> + */
>>>>> +u64 hv_do_fast_hypercall16(u16 code, u64 input1, u64 input2)
>>>>> +{
>>>>> +	struct arm_smccc_res	res;
>>>>> +	u64			control;
>>>>> +
>>>>> +	control = (u64)code | HV_HYPERCALL_FAST_BIT;
>>>>> +
>>>>> +	arm_smccc_1_1_hvc(HV_FUNC_ID, control, input1, input2, &res);
>>>>> +	return res.a0;
>>>>> +}
>>>>> +EXPORT_SYMBOL_GPL(hv_do_fast_hypercall16);
>>>>> +
>>>>
>>>> I'd like this to have been in arch/arm64/include/asm/mshyperv.h like its x86
>>>> counterpart, but that's just my personal liking of symmetry. I see why it's here
>>>> with its slow and 8-byte brethren.
>>>>
>>> Good point, I don't see a good reason this can't be in the header.
>>
>> I was trying to remember if there was some reason I originally put
>> hv_do_hypercall() and hv_do_fast_hypercall8() in the .c file instead of
>> the header like on x86. But I don't remember a reason. During
>> development, the code changed several times, and there might have
>> been a reason that didn't persistent in the version that was finally
>> accepted upstream.
>>
>> My only comment is that hv_do_hypercall() and the 8 and 16 "fast"
>> versions should probably stay together one place on the arm64 side,
>> even if it doesn't match x86.
>>
> 
> I think I'll just keep them together here for now then. They
> could be moved to the header in future if it seems worth doing.
> 

I was really hoping the answer here would be to move all of them together to the header,
but oh well.

<snip>