RE: [PATCH v2 4/6] arm64/hyperv: Boot in a Virtual Trust Level

Michael Kelley
2024-05-15T13:39:32Z

From: Roman Kisel <romank@linux.microsoft.com> Sent: Tuesday, May 14, 2024 3:44 PM
>
> To run in the VTL mode, Hyper-V drivers have to know what
> VTL the system boots in, and the arm64/hyperv code does not
> update the variable that stores the value.
>
> Update the variable to enable the Hyper-V drivers to boot
> in the VTL mode and print the VTL the code runs in.
>
> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> ---
> arch/arm64/hyperv/Makefile | 1 +
> arch/arm64/hyperv/hv_vtl.c | 19 +++++++++++++++++++
> arch/arm64/hyperv/mshyperv.c | 6 ++++++
> arch/arm64/include/asm/mshyperv.h | 8 ++++++++
> arch/x86/hyperv/hv_vtl.c | 2 +-
> 5 files changed, 35 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/hyperv/hv_vtl.c
>
> diff --git a/arch/arm64/hyperv/Makefile b/arch/arm64/hyperv/Makefile
> index 87c31c001da9..9701a837a6e1 100644
> --- a/arch/arm64/hyperv/Makefile
> +++ b/arch/arm64/hyperv/Makefile
> @@ -1,2 +1,3 @@
> # SPDX-License-Identifier: GPL-2.0
> obj-y := hv_core.o mshyperv.o
> +obj-$(CONFIG_HYPERV_VTL_MODE) += hv_vtl.o
> diff --git a/arch/arm64/hyperv/hv_vtl.c b/arch/arm64/hyperv/hv_vtl.c
> new file mode 100644
> index 000000000000..9b44cc49594c
> --- /dev/null
> +++ b/arch/arm64/hyperv/hv_vtl.c
> @@ -0,0 +1,19 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2023, Microsoft, Inc.
> + *
> + * Author : Roman Kisel <romank@linux.microsoft.com>
> + */
> +
> +#include <asm/mshyperv.h>
> +
> +void __init hv_vtl_init_platform(void)
> +{
> + pr_info("Linux runs in Hyper-V Virtual Trust Level %d\n", ms_hyperv.vtl);
> +}
> +
> +int __init hv_vtl_early_init(void)
> +{
> + return 0;
> +}
> +early_initcall(hv_vtl_early_init);
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> index 208a3bcb9686..cbde483b167a 100644
> --- a/arch/arm64/hyperv/mshyperv.c
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -96,6 +96,12 @@ static int __init hyperv_init(void)
> return ret;
> }
>
> + /* Find the VTL */
> + ms_hyperv.vtl = get_vtl();
> + if (ms_hyperv.vtl > 0) /* non default VTL */
> + hv_vtl_early_init();

Since hv_vtl_early_init() doesn't do anything on arm64, is the above
and the empty implementation of hv_vtl_early_init() really needed?
I thought maybe a subsequent patch in this series would populate
hv_vtl_early_init() to do something, but I didn't see such. I realize
the functions hv_vtl_init_platform() and hv_vtl_early_init() parallel
equivalent functions on x86, but I'd say drop hv_vtl_early_init() on
arm64 if it isn't needed.

Note too that the naming on the x86 side is arguably a bit messed
up. hv_vtl_init_platform() runs *before* hv_vtl_early_init(). But
typically in the Linux kernel, functions with "early init" in the name
run very early in boot, and that's not the case here. hv_vtl_init_platform()
is actually the function that runs very early in boot, but its name is
set up to parallel ms_hyperv_init_platform(), which calls it. On the
x86 side, I'd would argue for renaming hv_vtl_init_platform() to
hv_vtl_early_init(), and then hv_vtl_early_init() becomes hv_vtl_init().
But that's probably a separate patch. Here on arm64, perhaps all
you need is hv_vtl_init().

Michael

> +
> + hv_vtl_init_platform();
> ms_hyperv_late_init();
>
> hyperv_initialized = true;
> diff --git a/arch/arm64/include/asm/mshyperv.h
> b/arch/arm64/include/asm/mshyperv.h
> index a975e1a689dd..4a8ff6be389c 100644
> --- a/arch/arm64/include/asm/mshyperv.h
> +++ b/arch/arm64/include/asm/mshyperv.h
> @@ -49,6 +49,14 @@ static inline u64 hv_get_msr(unsigned int reg)
> ARM_SMCCC_OWNER_VENDOR_HYP, \
> HV_SMCCC_FUNC_NUMBER)
>
> +#ifdef CONFIG_HYPERV_VTL_MODE
> +void __init hv_vtl_init_platform(void);
> +int __init hv_vtl_early_init(void);
> +#else
> +static inline void __init hv_vtl_init_platform(void) {}
> +static inline int __init hv_vtl_early_init(void) { return 0; }
> +#endif
> +
> #include <asm-generic/mshyperv.h>
>
> #endif
> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
> index 92bd5a55f093..ae3105375a12 100644
> --- a/arch/x86/hyperv/hv_vtl.c
> +++ b/arch/x86/hyperv/hv_vtl.c
> @@ -19,7 +19,7 @@ static struct real_mode_header hv_vtl_real_mode_header;
>
> void __init hv_vtl_init_platform(void)
> {
> - pr_info("Linux runs in Hyper-V Virtual Trust Level\n");
> + pr_info("Linux runs in Hyper-V Virtual Trust Level %d\n", ms_hyperv.vtl);
>
> x86_platform.realmode_reserve = x86_init_noop;
> x86_platform.realmode_init = x86_init_noop;
> --
> 2.45.0
>