On Thu, Mar 20, 2025 at 05:11:25PM +0000, Suzuki K Poulose wrote: > On 20/03/2025 17:09, Mikołaj Lenczewski wrote: > > On Thu, Mar 20, 2025 at 01:24:25PM +0000, Suzuki K Poulose wrote: > > > On 19/03/2025 15:05, Mikołaj Lenczewski wrote: > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > > > index fb8752b42ec8..3e4cc917a07e 100644 > > > > --- a/Documentation/admin-guide/kernel-parameters.txt > > > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > > > @@ -453,6 +453,9 @@ > > > > arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of > > > > 32 bit applications. > > > > + arm64.nobbml2 [ARM64] Unconditionally disable Break-Before-Make Level > > > > + 2 support > > > > + > > > > arm64.nobti [ARM64] Unconditionally disable Branch Target > > > > Identification support > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > > > index 940343beb3d4..49deda2b22ae 100644 > > > > --- a/arch/arm64/Kconfig > > > > +++ b/arch/arm64/Kconfig > > > > @@ -2057,6 +2057,17 @@ config ARM64_TLB_RANGE > > > > The feature introduces new assembly instructions, and they were > > > > support when binutils >= 2.30. > > > > +config ARM64_BBML2_NOABORT > > > > + bool "Enable support for Break-Before-Make Level 2 detection and usage" > > > > + default y > > > > + help > > > > + FEAT_BBM provides detection of support levels for break-before-make > > > > + sequences. If BBM level 2 is supported, some TLB maintenance requirements > > > > + can be relaxed to improve performance. We additonally require the > > > > + property that the implementation cannot ever raise TLB Conflict Aborts. > > > > + Selecting N causes the kernel to fallback to BBM level 0 behaviour > > > > + even if the system supports BBM level 2. > > > > > > minor nit: Should we mention that the feature can be disabled at runtime > > > using a kernel parameter ? > > > > Yes, this sounds very reasonable, I should have thought of that. Will > > mention the commandline parameter in the kconfig option documentation. > > And also may be mention this in the patch description and may be also > add the rationale for providing this tunable. > > Cheers > Suzuki > Will do! :) -- Kind regards, Mikołaj Lenczewski
