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

Michael Kelley
2025-03-06T19:05:46Z

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.

>
> >> /*
> >> * 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.

Michael

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