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

Roman Kisel
2024-05-15T18:13:47Z

On 5/15/2024 6:39 AM, Michael Kelley wrote:
> 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().
>
I'll clean that up, appreciate the thorough explanation!

> 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
>>

--
Thank you,
Roman