On Tue, 16 Nov 2021 10:47:37 +0100 Ard Biesheuvel <ardb@xxxxxxxxxx> 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. A Fixes: link would be helpful. kmap_local() was a year ago, so is a -stable backport desired here?
