Re: [PATCH v5 2/8] arm64: hyperv: Add hypercall and register access functions

[Boqun Feng]

Hi Michael,

On Thu, Oct 03, 2019 at 07:03:19PM +0000, Michael Kelley wrote:
> Add ARM64-specific code to make Hyper-V hypercalls and to
> access virtual processor synthetic registers via hypercalls.
> Hypercalls use a Hyper-V specific calling sequence with a non-zero
> immediate value per Section 2.9 of the SMC Calling Convention
> spec.
> 
> This code is architecture dependent and is mostly driven by
> architecture independent code in the VMbus driver and the
> Hyper-V timer clocksource driver.
> 
> This code is built only when CONFIG_HYPERV is enabled.
> 
> Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> ---
>  MAINTAINERS                 |   1 +
>  arch/arm64/Kbuild           |   1 +
>  arch/arm64/hyperv/Makefile  |   2 +
>  arch/arm64/hyperv/hv_hvc.S  |  44 +++++++++++++++
>  arch/arm64/hyperv/hv_init.c | 133 ++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 181 insertions(+)
>  create mode 100644 arch/arm64/hyperv/Makefile
>  create mode 100644 arch/arm64/hyperv/hv_hvc.S
>  create mode 100644 arch/arm64/hyperv/hv_init.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index d464067..84f76f9 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7566,6 +7566,7 @@ F:	arch/x86/kernel/cpu/mshyperv.c
>  F:	arch/x86/hyperv
>  F:	arch/arm64/include/asm/hyperv-tlfs.h
>  F:	arch/arm64/include/asm/mshyperv.h
> +F:	arch/arm64/hyperv
>  F:	drivers/clocksource/hyperv_timer.c
>  F:	drivers/hid/hid-hyperv.c
>  F:	drivers/hv/
> diff --git a/arch/arm64/Kbuild b/arch/arm64/Kbuild
> index d646582..2469421 100644
> --- a/arch/arm64/Kbuild
> +++ b/arch/arm64/Kbuild
> @@ -3,4 +3,5 @@ obj-y			+= kernel/ mm/
>  obj-$(CONFIG_NET)	+= net/
>  obj-$(CONFIG_KVM)	+= kvm/
>  obj-$(CONFIG_XEN)	+= xen/
> +obj-$(CONFIG_HYPERV)	+= hyperv/

I did a kernel built with CONFIG_HYPERV=m today, and found out this line
should be (similar to x86):

	+obj-$(subst m,y,$(CONFIG_HYPERV))      += hyperv/

, otherwise, when CONFIG_HYPERV=m, files in arch/arm64/hyperv/ will be
compiled as obj-m, and symbols defined in those files cannot be
used by kernel builtin, e.g. hyperv_timer (since CONFIG_HYPERV_TIMER=y
in this case).

A compile/link error I hit today is:

| /home/boqun/linux-arm64/drivers/clocksource/hyperv_timer.c:98: undefined reference to `hv_set_vpreg'
| aarch64-linux-gnu-ld: /home/boqun/linux-arm64/drivers/clocksource/hyperv_timer.c:98: undefined reference to `hv_set_vpreg'

[...]

Besides, another problem I hit when compiled with CONFIG_HYPERV=m is:

| ERROR: "screen_info" [drivers/hv/hv_vmbus.ko] undefined!

, which can be fixed by the following change.

Regards,
Boqun

---------------->8
diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index d0cf596db82c..8ff557ae5cc6 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c

@@ -55,6 +55,7 @@ static __init pteval_t create_mapping_protection(efi_memory_desc_t *md)

 /* we will fill this structure from the stub, so don't put it in .bss */
 struct screen_info screen_info __section(.data);
+EXPORT_SYMBOL(screen_info);

 int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md)
 {