Messages in this thread | | | Date | Thu, 4 Feb 2021 10:47:15 +0000 | From | Russell King - ARM Linux admin <> | Subject | Re: next/master bisection: baseline.login on rk3288-rock2-square |
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On Thu, Feb 04, 2021 at 11:27:16AM +0100, Ard Biesheuvel wrote: > Hi Russell, > > If Guillaume is willing to do the experiment, and it fixes the issue, > it proves that rk3288 is relying on the flush before the MMU is > disabled, and so in that case, the fix is trivial, and we can just > apply it. > > If the experiment fails (which would mean rk3288 does not tolerate the > cache maintenance being performed after cache off), it is going to be > hairy, and so it will definitely take more time. > > So in the latter case (or if Guillaume does not get back to us), I > think reverting my queued fix is the only sane option. But in that > case, may I suggest that we queue the revert of the original by-VA > change for v5.12 so it gets lots of coverage in -next, and allows us > an opportunity to come up with a proper fix in the same timeframe, and > backport the revert and the subsequent fix as a pair? Otherwise, we'll > end up in the situation where v5.10.x until today has by-va, v5.10.x-y > has set/way, and v5.10y+ has by-va again. (I don't think we care about > anything before that, given that v5.4 predates any of this)
I'm suggesting dropping your fix (9052/1) and reverting "ARM: decompressor: switch to by-VA cache maintenance for v7 cores" which gets us to a point where _both_ regressions are fixed.
I'm of the opinion that the by-VA patch was incorrect when it was merged (it caused a regression), and it's only a performance improvement. Our attempts so far to fix it are just causing other regressions. So, I think it is reasonable to revert both back to a known good point which has worked over a decade. If doing so causes regressions (which I think is unlikely), then that would be unfortunate but alas is a price that's worth paying to get back to a known good point - since then we're not stacking regression fixes on top of other regression fixes.
-- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
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