On Thu, Mar 13, 2025 at 04:13:22PM +0000, Ryan Roberts wrote:
> On 13/03/2025 10:41, Mikołaj Lenczewski wrote:
> > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > index d561cf3b8ac7..b936e0805161 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -2176,6 +2176,76 @@ static bool hvhe_possible(const struct arm64_cpu_capabilities *entry,
> > return arm64_test_sw_feature_override(ARM64_SW_FEATURE_OVERRIDE_HVHE);
> > }
> >
> > +static inline bool bbml2_possible(void)
> > +{
> > + return !arm64_test_sw_feature_override(ARM64_SW_FEATURE_OVERRIDE_NOBBML2);
>
> If you're going to keep this helper, I think it really needs to be:
>
> return IS_ENABLED(CONFIG_ARM64_BBML2_NOABORT) &&
> !arm64_test_sw_feature_override(ARM64_SW_FEATURE_OVERRIDE_NOBBML2);
>
> Then you would simplify the caller to remove it's own
> IS_ENABLED(CONFIG_ARM64_BBML2_NOABORT) check.
>
> But personally I would remove the helper and just fold the test into
> has_bbml2_noabort().
>
> Thanks,
> Ryan
I was debating folding it into has_bbml2_noabort(), but went ahead and
implemented it separately to match hvhe_possible(), which was another sw
feature helper.
But I agree, folding it will be simpler and read just as easily (if not
easier). Will do so.
> > +}
> > +
> > +static bool cpu_has_bbml2_noabort(unsigned int cpu_midr)
> > +{
> > + /* We want to allow usage of bbml2 in as wide a range of kernel contexts
> > + * as possible. This list is therefore an allow-list of known-good
> > + * implementations that both support bbml2 and additionally, fulfill the
> > + * extra constraint of never generating TLB conflict aborts when using
> > + * the relaxed bbml2 semantics (such aborts make use of bbml2 in certain
> > + * kernel contexts difficult to prove safe against recursive aborts).
> > + *
> > + * Note that implementations can only be considered "known-good" if their
> > + * implementors attest to the fact that the implementation never raises
> > + * TLBI conflict aborts for bbml2 mapping granularity changes.
> > + */
> > + static const struct midr_range supports_bbml2_noabort_list[] = {
> > + MIDR_REV_RANGE(MIDR_CORTEX_X4, 0, 3, 0xf),
> > + MIDR_REV_RANGE(MIDR_NEOVERSE_V3, 0, 2, 0xf),
> > + {}
> > + };
> > +
> > + return is_midr_in_range_list(cpu_midr, supports_bbml2_noabort_list);
> > +}
> > +
> > +static inline unsigned int __cpu_read_midr(int cpu)
>
> nit: why the double underscrore prefix?
Again copying other helpers I saw that seemed to do similar things.
Didn't know if this was the expected style, so did as other helpers did.
Will remove.
Thank you for the review.
--
Kind regards,
Mikołaj Lenczewski
