On Thu, Feb 04, 2021 at 03:25:20PM +0100, Ard Biesheuvel wrote: > Pushing contents of the cache hierarchy to main memory is *not* a > valid use of set/way ops, and so there is no point in pretending that > set/way ops will produce the same results as by-VA ops. Only the by-VA > ops give the architectural guarantees that we rely on for correctness.
... yet we /were/ doing that, and it worked fine for 13 years - from 1st June 2007 until the by-VA merge into mainline on the 3rd April 2020. You may be right that it wasn't the most correct way, but it worked for those 13 years without issue, and it's only recently that it's become a problem, and trying to "fix" that introduced a regression, and fixing that regression has caused another regression... and I what I'm wondering is how many more regression fixing cycles it's going to take - how many regression fixes on top of other regression fixes are we going to end up seeing here. The fact is, we never properly understood why your patch caused the regression I was seeing. If we don't understand it, then we can never say that we've fixed the problem properly. That is highlighted by the fact that fixing the regression I was seeing has caused another regression. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!