On Wed, Mar 10, 2021 at 08:10:42PM +0100, David Hildenbrand wrote: > > > > > Memory gets allocated and used in a different order, which seems to have > > > > exposed (yet another) latent BUG. > > > > > > Well, you can call it that, or you can say that things worked under > > > certain assumptions regarding the memory allocation order which are > > > not met any more. Regardless of the assumptions in the page allocator we had a page used by the firmware on a free list, which is a bug. > > > > The same could be reproduced via zone shuffling with a little luck. > > > > > > But nobody does that in practice. > > > > > Dan will most certainly object. And I don't know what makes you speak in > absolute words here. > > > > This would be relatively straightforward to address if ACPICA was not > > > involved in it, but unfortunately that's not the case. > > > > > > Changing this part of ACPICA is risky, because such changes may affect > > > other OSes using it, so that requires some serious consideration. > > > Alternatively, the previous memory allocation order in Linux could be > > > restored. > > > > Of course, long-term this needs to be addressed in the ACPI > > initialization code, because it clearly is not robust enough, but in > > the meantime there's practical breakage observable in the field, so > > what can be done about that? > > *joke* enable zone shuffling. > > No seriously, fix the latent BUG. What again is problematic about excluding > these pages from the page allcoator, for example, via memblock_reserve()? > > @Mike? There is some care that should be taken to make sure we get the order right, but I don't see a fundamental issue here. If I understand correctly, Rafael's concern is about changing the parts of ACPICA that should be OS agnostic, so I think we just need another place to call memblock_reserve() rather than acpi_tb_install_table_with_override(). Since the reservation should be done early in x86::setup_arch() (and probably in arm64::setup_arch()) we might just have a function that parses table headers and reserves them, similarly to how we parse the tables during KASLR setup. -- Sincerely yours, Mike.
