RE: [PATCH v10 2/7] arm64: hyperv: Add Hyper-V hypercall and register access utilities

[Michael Kelley <mikelley@microsoft.com>]

From: Mark Rutland <mark.rutland@arm.com> Sent: Friday, May 14, 2021 5:53 AM
> 
> On Wed, May 12, 2021 at 10:37:42AM -0700, Michael Kelley wrote:
> > hyperv-tlfs.h defines Hyper-V interfaces from the Hyper-V Top Level
> > Functional Spec (TLFS), and #includes the architecture-independent
> > part of hyperv-tlfs.h in include/asm-generic.  The published TLFS
> > is distinctly oriented to x86/x64, so the ARM64-specific
> > hyperv-tlfs.h includes information for ARM64 that is not yet formally
> > published. The TLFS is available here:
> >
> >   docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs
> >
> > mshyperv.h defines Linux-specific structures and routines for
> > interacting with Hyper-V on ARM64, and #includes the architecture-
> > independent part of mshyperv.h in include/asm-generic.
> >
> > Use these definitions to provide utility functions to make
> > Hyper-V hypercalls and to get and set Hyper-V provided
> > registers associated with a virtual processor.
> >
> > Signed-off-by: Michael Kelley <mikelley@microsoft.com>
> > Reviewed-by: Sunil Muthuswamy <sunilmut@microsoft.com>
> > ---
> >  MAINTAINERS                          |   3 +
> >  arch/arm64/Kbuild                    |   1 +
> >  arch/arm64/hyperv/Makefile           |   2 +
> >  arch/arm64/hyperv/hv_core.c          | 130 +++++++++++++++++++++++++++++++++++
> >  arch/arm64/include/asm/hyperv-tlfs.h |  69 +++++++++++++++++++
> >  arch/arm64/include/asm/mshyperv.h    |  54 +++++++++++++++
> >  6 files changed, 259 insertions(+)
> >  create mode 100644 arch/arm64/hyperv/Makefile
> >  create mode 100644 arch/arm64/hyperv/hv_core.c
> >  create mode 100644 arch/arm64/include/asm/hyperv-tlfs.h
> >  create mode 100644 arch/arm64/include/asm/mshyperv.h
> 
> > +/*
> > + * hv_do_hypercall- Invoke the specified hypercall
> > + */
> > +u64 hv_do_hypercall(u64 control, void *input, void *output)
> > +{
> > +	struct arm_smccc_res	res;
> > +	u64			input_address;
> > +	u64			output_address;
> > +
> > +	input_address = input ? virt_to_phys(input) : 0;
> > +	output_address = output ? virt_to_phys(output) : 0;
> 
> I may have asked this before, but are `input` and `output` always linear
> map pointers, or can they ever be vmalloc pointers?
> 
> Otherwise, this looks fine to me.
> 

The caller must ensure that hypercall arguments are aligned to
4 Kbytes, and no larger than 4 Kbytes, since that's the page size
used by Hyper-V regardless of the guest page size.  A per-CPU
4 Kbyte memory area (hyperv_pcpu_input_arg) meeting these
requirements is pre-allocated that callers can use for this purpose.
On the x86 side there's also a similar hyperv_pcpu_output_arg,
but there are no use cases for it on ARM64.

Michael