Re: [PATCH v5 01/12] xen/arm: enable SVE extension for Xen

[Luca Fancellu <Luca.Fancellu@arm.com>]

> On 13 Apr 2023, at 13:47, Bertrand Marquis <Bertrand.Marquis@arm.com> wrote:
> 
> Hi Luca,
> 
>> On 12 Apr 2023, at 11:49, Luca Fancellu <Luca.Fancellu@arm.com> wrote:
>> 
>> Enable Xen to handle the SVE extension, add code in cpufeature module
>> to handle ZCR SVE register, disable trapping SVE feature on system
>> boot only when SVE resources are accessed.
>> While there, correct coding style for the comment on coprocessor
>> trapping.
>> 
>> Now cptr_el2 is part of the domain context and it will be restored
>> on context switch, this is a preparation for saving the SVE context
>> which will be part of VFP operations, so restore it before the call
>> to save VFP registers.
>> To save an additional isb barrier, restore cptr_el2 before an
>> existing isb barrier and move the call for saving VFP context after
>> that barrier.
>> 
>> Change the KConfig entry to make ARM64_SVE symbol selectable, by
>> default it will be not selected.
>> 
>> Create sve module and sve_asm.S that contains assembly routines for
>> the SVE feature, this code is inspired from linux and it uses
>> instruction encoding to be compatible with compilers that does not
>> support SVE.
>> 
>> Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
>> ---
>> Changes from v4:
>> - don't use fixed types in vl_to_zcr, forgot to address that in
>>  v3, by mistake I changed that in patch 2, fixing now (Jan)
>> Changes from v3:
>> - no changes
>> Changes from v2:
>> - renamed sve_asm.S in sve-asm.S, new files should not contain
>>  underscore in the name (Jan)
>> Changes from v1:
>> - Add assert to vl_to_zcr, it is never called with vl==0, but just
>>  to be sure it won't in the future.
>> Changes from RFC:
>> - Moved restoring of cptr before an existing barrier (Julien)
>> - Marked the feature as unsupported for now (Julien)
>> - Trap and un-trap only when using SVE resources in
>>  compute_max_zcr() (Julien)
>> ---
>> xen/arch/arm/Kconfig                     | 10 +++--
>> xen/arch/arm/arm64/Makefile              |  1 +
>> xen/arch/arm/arm64/cpufeature.c          |  7 ++--
>> xen/arch/arm/arm64/sve-asm.S             | 48 +++++++++++++++++++++++
>> xen/arch/arm/arm64/sve.c                 | 50 ++++++++++++++++++++++++
>> xen/arch/arm/cpufeature.c                |  6 ++-
>> xen/arch/arm/domain.c                    |  9 +++--
>> xen/arch/arm/include/asm/arm64/sve.h     | 43 ++++++++++++++++++++
>> xen/arch/arm/include/asm/arm64/sysregs.h |  1 +
>> xen/arch/arm/include/asm/cpufeature.h    | 14 +++++++
>> xen/arch/arm/include/asm/domain.h        |  1 +
>> xen/arch/arm/include/asm/processor.h     |  2 +
>> xen/arch/arm/setup.c                     |  5 ++-
>> xen/arch/arm/traps.c                     | 28 +++++++------
>> 14 files changed, 201 insertions(+), 24 deletions(-)
>> create mode 100644 xen/arch/arm/arm64/sve-asm.S
>> create mode 100644 xen/arch/arm/arm64/sve.c
>> create mode 100644 xen/arch/arm/include/asm/arm64/sve.h
>> 
>> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
>> index 239d3aed3c7f..41f45d8d1203 100644
>> --- a/xen/arch/arm/Kconfig
>> +++ b/xen/arch/arm/Kconfig
>> @@ -112,11 +112,15 @@ config ARM64_PTR_AUTH
>> This feature is not supported in Xen.
>> 
>> config ARM64_SVE
>> - def_bool n
>> + bool "Enable Scalar Vector Extension support (UNSUPPORTED)" if UNSUPPORTED
>> depends on ARM_64
>> help
>> -  Scalar Vector Extension support.
>> -  This feature is not supported in Xen.
>> +  Scalar Vector Extension (SVE/SVE2) support for guests.
> 
> I would prevent to mention SVE2 here unless both versions of SVE are supported with this config.
> Is it the case ?

Hi Bertrand,

Yes both versions of SVE are supported with this config, SVE2 is a superset of SVE that includes new
instructions, but the work done in this serie for registers settings and context switch will apply to both
versions.

> 
> Cheers
> Bertrand