On Tue, Nov 16, 2021 at 10:47:37AM +0100, Ard Biesheuvel wrote: > The kmap_local conversion broke the ARM architecture, because the new > code assumes that all PTEs used for creating kmaps form a linear array > in memory, and uses array indexing to look up the kmap PTE belonging to > a certain kmap index. > > On ARM, this cannot work, not only because the PTE pages may be > non-adjacent in memory, but also because ARM/!LPAE interleaves hardware > entries and extended entries (carrying software-only bits) in a way that > is not compatible with array indexing. > > Fortunately, this only seems to affect configurations with more than 8 > CPUs, due to the way the per-CPU kmap slots are organized in memory. > > Work around this by permitting an architecture to set a Kconfig symbol > that signifies that the kmap PTEs do not form a lineary array in memory, > and so the only way to locate the appropriate one is to walk the page > tables. > > Link: https://lore.kernel.org/linux-arm-kernel/20211026131249.3731275-1-ardb@xxxxxxxxxx/ > Reported-by: Quanyang Wang <quanyang.wang@xxxxxxxxxxxxx> > Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Russell King <linux@xxxxxxxxxxxxxxx> Acked-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx> Thanks. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
