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

[Ryan Roberts <ryan.roberts@arm.com>]

On 13/11/2023 13:27, Catalin Marinas wrote:
> On Mon, Nov 13, 2023 at 11:55:01AM +0000, Ryan Roberts wrote:
>> On 27/10/2023 12:56, Ryan Roberts wrote:
>>> 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.
> [...]
>> 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.
> 
> I suspect that's what most maintainers wait for ;). Usually patches
> posted just before or during the merging window get ignored, unless they
> are urgent fixes.
> 
>> 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.
> 
> If these patches are needed for Ard's series (I think they do), they
> could be posted together. But first we need to split Ard's series into
> at least two: reworking the memory map together with moving (some of)
> the init code to C and the actual LPA2 stage 1 support. We might even
> through LPA2 stage 2 on top if we feel brave ;). We can queue them all
> together but having separate series gives us an option to drop bits if
> needed.

Sorry I'm not completely sure what you are suggesting I do here. In the context
of the lpa2/kvm series, Marc previously said he would merge it for v6.8 if I
posted against v6.7-rc1 (which is what I'm gearing up for now).

My series and Ard's are independent except that they both depend on the 3
patches in this RFC. Ard has just suggested he would prefix his series with
these 3 patches and I would continue to do the same, then they can be handled as
2 independent series (or more if Ard is splitting his) - the first 3 patches
will just desolve to nothing for the series that goes in second.

Does that work for you, are are you suggesting I should re-post this as an
independent series?

Thanks,
Ryan