Re: [PATCH v2 2/6] drivers/hv: Enable VTL mode for arm64

Roman Kisel
2024-05-15T18:04:14Z

On 5/15/2024 6:37 AM, Michael Kelley wrote:
> From: Roman Kisel <romank@linux.microsoft.com> Sent: Tuesday, May 14, 2024 3:44 PM
>>
>> Kconfig dependencies for arm64 guests on Hyper-V require that be ACPI enabled,
>> and limit VTL mode to x86/x64. To enable VTL mode on arm64 as well, update the
>> dependencies. Since VTL mode requires DeviceTree instead of ACPI, don't require
>> arm64 guests on Hyper-V to have ACPI.
>>
>> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
>> ---
>> drivers/hv/Kconfig | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
>> index 862c47b191af..a5cd1365e248 100644
>> --- a/drivers/hv/Kconfig
>> +++ b/drivers/hv/Kconfig
>> @@ -5,7 +5,7 @@ menu "Microsoft Hyper-V guest support"
>> config HYPERV
>> tristate "Microsoft Hyper-V client drivers"
>> depends on (X86 && X86_LOCAL_APIC && HYPERVISOR_GUEST) \
>> - || (ACPI && ARM64 && !CPU_BIG_ENDIAN)
>> + || (ARM64 && !CPU_BIG_ENDIAN)
>> select PARAVIRT
>> select X86_HV_CALLBACK_VECTOR if X86
>> select OF_EARLY_FLATTREE if OF
>> @@ -15,7 +15,7 @@ config HYPERV
>>
>> config HYPERV_VTL_MODE
>> bool "Enable Linux to boot in VTL context"
>> - depends on X86_64 && HYPERV
>> + depends on HYPERV
>> depends on SMP
>> default n
>> help
>
> These changes make it possible to build a normal VTL 0 Hyper-V
> guest (i.e., CONFIG_HYPERV_VTL_MODE=n) if CONFIG_ACPI is
> not set, which won't work. While we can say "don't do that", it
> would be better if the Kconfig dependencies expressed that
> requirement.
>
> A possible fix is to remove the "depends on HYPERV" from
> HYPERV_VTL_MODE. Then for HYPERV, make
> the "depends on ACPI" be conditional on !HYPERV_VTL_MODE
> (for both ARM64 and X86).
>
> I think we originally had "depends on HYPERV" in
> HYPERV_VTL_MODE because there was a VTL-related function
> in a non-Hyper-V code path, and we wanted to prevent that code
> from running in non-Hyper-V environments. But in practice, that
> turned out not to work well because occasionally people would
> do an "all config" build where both CONFIG_HYPERV and
> CONFIG_HYPERV_VTL_MODE were set, and it would panic during
> boot in their non-Hyper-V environment. Such people were not
> happy. :-( So Saurabh made a relatively simple change (see commit
> 14058f72cf13e) that got the VTL code out of that non-Hyper-V code
> path. With that change, it shouldn't matter if someone sets
> CONFIG_HYPERV_VTL_MODE=y in a build where
> CONFIG_HYPERV=n.
>
> At least that's my theory. :-) Someone would need to check
> it carefully.
I'll explore that, appreciate sharing the context!

>
> Michael

--
Thank you,
Roman