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

[Ryan Roberts]

On 27/10/2023 12:56, Ryan Roberts wrote:
> 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.

Marc, All,

I polite bump; I never heard back on this. I'm planning to post my LPA2/KVM
series on top of v6.7-rc1 in the next day or 2. By default, these 3 patches will
be the first 3 of the series. But if you have an issue with the approach it
would be good to work out an alternative plan to avoid wasting effort preparing
the series.

Thanks,
Ryan

> 
> [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(-)
> 
> --
> 2.25.1
>