Hi Miko,
On 13/03/2025 10:41, Mikołaj Lenczewski wrote:
Hi All,
This patch series adds adding initial support for eliding
break-before-make requirements on systems that support BBML2 and
additionally guarantee to never raise a conflict abort.
This support elides a TLB invalidation in contpte_convert(). This
leads to a 12% improvement when executing a microbenchmark designed
to force the pathological path where contpte_convert() gets called.
This represents an 80% reduction in the cost of calling
contpte_convert().
This series is based on v6.14-rc4 (d082ecbc71e9).
Patch 1 implements an allow-list of cpus that support BBML2, but with
the additional constraint of never causing TLB conflict aborts. We
settled on this constraint because we will use the feature for kernel
mappings in the future, for which we cannot handle conflict aborts
safely.
Yang Shi has a series at [1] that aims to use BBML2 to enable splitting
the linear map at runtime. This series partially overlaps with it to add
the cpu feature. We believe this series is fully compatible with Yang's
requirements and could go first.
Nothing about the patch functionality, but :
Minor nit: Generally it is a good idea to add "What changed" from the
previous posting. That gives the reviewers an idea of what to look for
in the new version. Something like:
Changes since V2:
{Adding a link to the posting is an added bonus, as we can look up the
discussions easily}
- blah blah
- ..
Cheers
Suzuki
[1]:
https://lore.kernel.org/linux-arm-kernel/20250304222018.615808-1-yang@xxxxxxxxxxxxxxxxxxxxxx/
Mikołaj Lenczewski (3):
arm64: Add BBM Level 2 cpu feature
iommu/arm: Add BBM Level 2 smmu feature
arm64/mm: Elide tlbi in contpte_convert() under BBML2
.../admin-guide/kernel-parameters.txt | 3 +
arch/arm64/Kconfig | 11 +++
arch/arm64/include/asm/cpucaps.h | 2 +
arch/arm64/include/asm/cpufeature.h | 6 ++
arch/arm64/kernel/cpufeature.c | 76 +++++++++++++++++++
arch/arm64/kernel/pi/idreg-override.c | 2 +
arch/arm64/mm/contpte.c | 3 +-
arch/arm64/tools/cpucaps | 1 +
.../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c | 3 +
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 3 +
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 4 +
11 files changed, 113 insertions(+), 1 deletion(-)
