From: Mark Rutland <mark.rutland@xxxxxxx> Sent: Monday, August 2, 2021 9:26 AM
>
> On Tue, Jul 20, 2021 at 07:57:01AM -0700, Michael Kelley wrote:
> > Add ARM64-specific code to initialize the Hyper-V
> > hypervisor when booting as a guest VM.
> >
> > This code is built only when CONFIG_HYPERV is enabled.
> >
> > Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> > ---
> > arch/arm64/hyperv/Makefile | 2 +-
> > arch/arm64/hyperv/mshyperv.c | 83 ++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 84 insertions(+), 1 deletion(-)
> > create mode 100644 arch/arm64/hyperv/mshyperv.c
> >
> > diff --git a/arch/arm64/hyperv/Makefile b/arch/arm64/hyperv/Makefile
> > index 1697d30..87c31c0 100644
> > --- a/arch/arm64/hyperv/Makefile
> > +++ b/arch/arm64/hyperv/Makefile
> > @@ -1,2 +1,2 @@
> > # SPDX-License-Identifier: GPL-2.0
> > -obj-y := hv_core.o
> > +obj-y := hv_core.o mshyperv.o
> > diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> > new file mode 100644
> > index 0000000..2811fd0
> > --- /dev/null
> > +++ b/arch/arm64/hyperv/mshyperv.c
> > @@ -0,0 +1,83 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +/*
> > + * Core routines for interacting with Microsoft's Hyper-V hypervisor,
> > + * including hypervisor initialization.
> > + *
> > + * Copyright (C) 2021, Microsoft, Inc.
> > + *
> > + * Author : Michael Kelley <mikelley@xxxxxxxxxxxxx>
> > + */
> > +
> > +#include <linux/types.h>
> > +#include <linux/acpi.h>
> > +#include <linux/export.h>
> > +#include <linux/errno.h>
> > +#include <linux/version.h>
> > +#include <linux/cpuhotplug.h>
> > +#include <asm/mshyperv.h>
> > +
> > +static bool hyperv_initialized;
> > +
> > +static int __init hyperv_init(void)
> > +{
> > + struct hv_get_vp_registers_output result;
> > + u32 a, b, c, d;
> > + u64 guest_id;
> > + int ret;
>
> As Marc suggests, before looking at the FADT, you need something like:
>
> /*
> * Hyper-V VMs always have ACPI.
> */
> if (acpi_disabled)
> return 0;
>
> ... where `acpi_disabled` is defined in <linux/acpi.h> (or via its
> includes), so you don't need to include any additional headers.
>
> > +
> > + /*
> > + * If we're in a VM on Hyper-V, the ACPI hypervisor_id field will
> > + * have the string "MsHyperV".
> > + */
> > + if (strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8))
> > + return -EINVAL;
>
> As Marc suggests, it's no an error for a platform to not have Hyper-V,
> so returning 0 in tihs case would be preferable.
>
> Otherwise this looks fine to me.
>
Thanks Marc and Mark. Good point that the code should cleanly
handle the case where a kernel is built with CONFIG_HYPERV but
running somewhere other than as a Hyper-V guest.
Michael
