[RFC PATCH v1 0/3] Update tlb invalidation routines for FEAT_LPA2

[Ryan Roberts]

Hi All,

As raised yesterday against Ard's LPA2 series [1], we need to address the TLBI
changes to properly support LPA2 before Ard's changes get merged. So far those
changes have been part of my KVM LPA2 series [2]. So this is an attempt to split
the TLBI changes to make them independent. The idea is that this series would go
in first, then Ard's and the rest of my series can race eachother and it doesn't
really matter who wins.

I've attempted to address all of Marc's feedback against the versions of these
patches posted at [2], including adding benchmark data (see patch 1). Although
if people are still nervous that this could regress non-lpa2 performance in some
cases, I could rework so that there are lpa2 and non-lpa2 variants of
__flush_tlb_range_op(), and the correct version is chosen at the higher level
(based on lpa2_is_enabled() / kvm_lpa2_is_enabled()).

It turns out that we won't be able to key LPA2 usage off the same static key for
both the kernel and kvm usage because the kernel usage additionally depends on
CONFIG_ARM64_LPA2 being enabled. So I've introduced 2 stub functions
(lpa2_is_enabled() and kvm_lpa2_is_enabled()) to advertise it. Ard already
defines and implements lpa2_is_enabled() in his series, so there will be a minor
conflict to resolve there. I plan to define kvm_lpa2_is_enabled() to be the
static key for kvm in my series. Marc, would you be happy with this approach?

Anyway, I wanted to put this out there as an RFC. If we are happy with it, then
I'll re-post on 6.7-rc1.

[1] https://lore.kernel.org/linux-arm-kernel/5651bb31-9ef6-4dfc-b146-64606279bbf7@arm.com/
[2] https://lore.kernel.org/kvmarm/20231009185008.3803879-1-ryan.roberts@arm.com/

Thanks,
Ryan

Ryan Roberts (3):
  arm64/mm: Modify range-based tlbi to decrement scale
  arm64/mm: Add lpa2_is_enabled() kvm_lpa2_is_enabled() stubs
  arm64/mm: Update tlb invalidation routines for FEAT_LPA2

 arch/arm64/include/asm/kvm_mmu.h      |   3 +
 arch/arm64/include/asm/pgtable-prot.h |   2 +
 arch/arm64/include/asm/tlb.h          |  15 ++--
 arch/arm64/include/asm/tlbflush.h     | 100 ++++++++++++++++----------
 4 files changed, 78 insertions(+), 42 deletions(-)

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2.25.1