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SubjectRe: [PATCH 2/2] arm64: Support systems without FP/ASIMD
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On 25/10/16 15:00, Ard Biesheuvel wrote:
> Hi Suzuki,
>
> On 25 October 2016 at 14:50, Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>> The arm64 kernel assumes that FP/ASIMD units are always present
>> and accesses the FP/ASIMD specific registers unconditionally. This
>> could cause problems when they are absent. This patch adds the
>> support for kernel handling systems without FP/ASIMD by skipping the
>> register access within the kernel. For kvm, we trap the accesses
>> to FP/ASIMD and inject an undefined instruction exception to the VM.
>>
>> The callers of the exported kernel_neon_begin_parital() should
>> make sure that the FP/ASIMD is supported.
>>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will.deacon@arm.com>
>> Cc: Christoffer Dall <christoffer.dall@linaro.org>
>> Cc: Marc Zyngier <marc.zyngier@arm.com>
>> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> ---
>> ---
>> arch/arm64/crypto/aes-ce-ccm-glue.c | 2 +-
>> arch/arm64/crypto/aes-ce-cipher.c | 2 ++
>> arch/arm64/crypto/ghash-ce-glue.c | 2 ++
>> arch/arm64/crypto/sha1-ce-glue.c | 2 ++
>> arch/arm64/include/asm/cpufeature.h | 8 +++++++-
>> arch/arm64/include/asm/neon.h | 3 ++-
>> arch/arm64/kernel/cpufeature.c | 15 +++++++++++++++
>> arch/arm64/kernel/fpsimd.c | 14 ++++++++++++++
>> arch/arm64/kvm/handle_exit.c | 11 +++++++++++
>> arch/arm64/kvm/hyp/hyp-entry.S | 9 ++++++++-
>> arch/arm64/kvm/hyp/switch.c | 5 ++++-
>> 11 files changed, 68 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/crypto/aes-ce-ccm-glue.c b/arch/arm64/crypto/aes-ce-ccm-glue.c
>> index f4bf2f2..d001b4e 100644
>> --- a/arch/arm64/crypto/aes-ce-ccm-glue.c
>> +++ b/arch/arm64/crypto/aes-ce-ccm-glue.c
>> @@ -296,7 +296,7 @@ static struct aead_alg ccm_aes_alg = {
>>
>> static int __init aes_mod_init(void)
>> {
>> - if (!(elf_hwcap & HWCAP_AES))
>> + if (!(elf_hwcap & HWCAP_AES) || !system_supports_fpsimd())
>
> This looks weird to me. All crypto extensionsinstructions except CRC
> operate strictly on FP/ASIMD registers, and so support for FP/ASIMD is
> implied by having HWCAP_AES. In other words, I think it makes more
> sense to sanity check that the info registers are consistent with each
> other in core code than modifying each user (which for HWCAP_xxx
> includes userland) to double check that the world is sane.

You're right. I will respin it.
Btw, I think we need the following feature check for the above. I will send
that in and remove the explicit HWCAP_AES check.

module_cpu_feature_match(AES, aes_mod_init());

Cheers
Suzuki
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