On Fri, 2022-04-22 at 14:31 +1000, Nicholas Piggin wrote: > Any other concerns with the fix? I had another concern with the vmalloc huge pages. Possibly getting into paranoid territory here, but it's around the new behavior of freeing vmalloc page tables. At least on x86 this doesn't happen very often. AFAICT it all happens during boot or during memory hot unplug. The risk this entails is racing against all the software page table walks and walking a freed table. At least on x86 the walks of the kernel tables are done with no locks, which works because the PTE updates are atomic and pretty much never freed. Some of the kernel page table walks in the fault handler are actually triggerable from userspace. So it's in the category of "already there is a bug" or a little trouble someone could cause with a lot of effort. At least until PKS vmalloc memory shows up. Anyway, as long as we are going over this all again I thought it was worth bringing up.
