Re: [RFC 07/10] arm64/mm: Detect and enable FEAT_LPA2

[Suzuki K Poulose]

On 16/07/2021 08:06, Anshuman Khandual wrote:
> On 7/14/21 1:51 PM, Suzuki K Poulose wrote:
> > On 14/07/2021 03:21, Anshuman Khandual wrote:
> > > Detect FEAT_LPA2 implementation early enough during boot when requested via
> > > CONFIG_ARM64_PA_BITS_52_LPA2 and remember in a variable arm64_lpa2_enabled.
> > > This variable could then be used to turn on TCR_EL1.TCR_DS effecting the 52
> > > bits PA range or fall back to default 48 bits PA range if FEAT_LPA2 feature
> > > was requested but found not to be implemented.
> > >
> > > Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> > > ---
> > >    arch/arm64/include/asm/memory.h |  1 +
> > >    arch/arm64/kernel/head.S        | 15 +++++++++++++++
> > >    arch/arm64/mm/mmu.c             |  3 +++
> > >    arch/arm64/mm/proc.S            |  9 +++++++++
> > >    4 files changed, 28 insertions(+)
> > >
> > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> > > index 824a365..d0ca002 100644
> > > --- a/arch/arm64/include/asm/memory.h
> > > +++ b/arch/arm64/include/asm/memory.h
> > > @@ -178,6 +178,7 @@
> > >    #include <asm/bug.h>
> > >      extern u64            vabits_actual;
> > > +extern u64            arm64_lpa2_enabled;
> > >      extern s64            memstart_addr;
> > >    /* PHYS_OFFSET - the physical address of the start of memory. */
> > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> > > index 6444147..9cf79ea 100644
> > > --- a/arch/arm64/kernel/head.S
> > > +++ b/arch/arm64/kernel/head.S
> > > @@ -94,6 +94,21 @@ SYM_CODE_START(primary_entry)
> > >        adrp    x23, __PHYS_OFFSET
> > >        and    x23, x23, MIN_KIMG_ALIGN - 1    // KASLR offset, defaults to 0
> > >        bl    set_cpu_boot_mode_flag
> > > +
> > > +#ifdef CONFIG_ARM64_PA_BITS_52_LPA2
> > > +    mrs     x10, ID_AA64MMFR0_EL1
> > > +    ubfx    x10, x10, #ID_AA64MMFR0_TGRAN_SHIFT, 4
> > > +    cmp     x10, #ID_AA64MMFR0_TGRAN_LPA2
> > > +    b.ne    1f
> >
> > For the sake of forward compatibility, this should be "b.lt"
> Right, I guess we could assume that the feature will be present from the
> current ID_AA64MMFR0_TGRAN_LPA2 values onward in the future. But should
> not this also be capped at ID_AA64MMFR0_TGRAN_SUPPORTED_MAX as the upper
> limit is different for 4K and 16K page sizes.

Absolutely.

Cheers
Suzuki

>