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

Nuno Das Neves
2025-03-07T21:37:07Z

On 3/6/2025 11:05 AM, Michael Kelley wrote:
> From: Nuno Das Neves <nunodasneves@linux.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@linux.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.

>>
>>>> /*
>>>> * Set a single VP register to a 64-bit value.
>>>> */
>>>> diff --git a/arch/arm64/include/asm/mshyperv.h
>> b/arch/arm64/include/asm/mshyperv.h
>>>> index 2e2f83bafcfb..2a900ba00622 100644
>>>> --- a/arch/arm64/include/asm/mshyperv.h
>>>> +++ b/arch/arm64/include/asm/mshyperv.h
>>>> @@ -40,6 +40,18 @@ static inline u64 hv_get_msr(unsigned int reg)
>>>> return hv_get_vpreg(reg);
>>>> }
>>>>
>>>> +/*
>>>> + * Nested is not supported on arm64
>>>> + */
>>>> +static inline void hv_set_non_nested_msr(unsigned int reg, u64 value)
>>>> +{
>>>> + hv_set_msr(reg, value);
>>>> +}
>>>
>>> empty line preferred here, also reported by checkpatch
>>>
>> Good point, missed that one...
>>
>>>> +static inline u64 hv_get_non_nested_msr(unsigned int reg)
>>>> +{
>>>> + return hv_get_msr(reg);
>>>> +}
>>>> +
>>>> /* SMCCC hypercall parameters */
>>>> #define HV_SMCCC_FUNC_NUMBER 1
>>>> #define HV_FUNC_ID ARM_SMCCC_CALL_VAL( \
>>>> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
>>>> index c020d5d0ec2a..258034dfd829 100644
>>>> --- a/include/asm-generic/mshyperv.h
>>>> +++ b/include/asm-generic/mshyperv.h
>>>> @@ -72,6 +72,8 @@ extern void * __percpu *hyperv_pcpu_output_arg;
>>>>
>>>> extern u64 hv_do_hypercall(u64 control, void *inputaddr, void *outputaddr);
>>>> extern u64 hv_do_fast_hypercall8(u16 control, u64 input8);
>>>> +extern u64 hv_do_fast_hypercall16(u16 control, u64 input1, u64 input2);
>>>> +
>>>
>>> checkpatch warns against putting externs in header files, and FWIW, if
>> hv_do_fast_hypercall16()
>>> for arm64 were in arch/arm64/include/asm/mshyperv.h like its x86 counterpart, you
>> probably
>>> wouldn't need this?
>>>
>> Yes I wondered about that warning. That's true, if I just put it in the arm64 header
>> then this won't be needed at all, so I might just do that!
>
> I always thought the checkpatch warning was simply that "extern" on a function
> declaration is superfluous. You can omit "extern" and nothing changes. Of
> course, the same is not true for data items.
> Good point, I think I'll clean up these "extern"s in the next version.

Nuno

> Michael
>
>>
>>>> bool hv_isolation_type_snp(void);
>>>> bool hv_isolation_type_tdx(void);
>>>>
>