[PATCH] ARM: advertise availability of v8 Crypto instructions

[Catalin Marinas]

On Tue, Mar 03, 2015 at 02:43:01PM +0100, Ard Biesheuvel wrote:
> On 27 February 2015 at 17:36, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> > When running the 32-bit ARM kernel on ARMv8 capable bare metal (e.g.,
> > 32-bit Android userland and kernel on a Cortex-A53), or as a KVM guest
> > on a 64-bit host, we should advertise the availability of the Crypto
> > instructions, so that userland libraries such as OpenSSL may use them.
> > (Support for the v8 Crypto instructions in the 32-bit build was added
> > to OpenSSL more than six months ago)
> >
> > This adds the ID feature bit detection, and sets elf_hwcap2 accordingly.
> >
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> > ---
> >  arch/arm/kernel/setup.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >
> > diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> > index e55408e96559..8d4cb1c1c9ac 100644
> > --- a/arch/arm/kernel/setup.c
> > +++ b/arch/arm/kernel/setup.c
> > @@ -393,6 +393,22 @@ static void __init cpuid_init_hwcaps(void)
> >         vmsa = (read_cpuid_ext(CPUID_EXT_MMFR0) & 0xf) >> 0;
> >         if (vmsa >= 5)
> >                 elf_hwcap |= HWCAP_LPAE;
> > +
> > +       /* check for supported v8 Crypto instructions on non v7-M CPUs */
> 
> Perhaps this should be 'on v7+ (non v7-M) CPUs'
> 
> > +       if (cpu_architecture() == CPU_ARCH_ARMv7) {
> 
> @Russell: any thoughts on this?
> 
> Currently, v8 CPUs are identified as CPU_ARCH_ARMv7, and there is no
> point in performing this test on other architectures (including v7-M)

With the new CPUID scheme introduced around v6/v7, the OS is no longer
meant to read much into the architecture version. Even the current
__get_cpu_architecture() function that we have returns the VMSA version
and not the actual CPU architecture version (for example, ARM11MPCore is
reported as ARMv7 by Linux when it's clearly an ARMv6). With ARMv8, the
ID_MMFR0 would still report VMSAv7 with LPAE (0b0101) like on a
Cortex-A15. You may be able to guess it's an ARMv8 from other fields
like ID_ISAR2[3:0] (acquire/release semantics for load/store) but that's
not how CPUID registers are meant to be used.

If we are bothered by the ARMv7 name, we could redefine some of these
macros to make it clear that the arch version is no longer relevant,
something like below (covering the profile names as well):

	CPU_ARCH_CPUID_A
	CPU_ARCH_CPUID_R
	CPU_ARCH_CPUID_M

Once you find such cpu arch number, you know you have access to the
architected CPUID registers.

-- 
Catalin