On Wed, Jun 04, 2025 at 09:39:30AM +0200, David Hildenbrand wrote: > On 03.06.25 21:22, Lorenzo Stoakes wrote: > > The walk_page_range_novma() function is rather confusing - it supports two > > modes, one used often, the other used only for debugging. > > > > The first mode is the common case of traversal of kernel page tables, which > > is what nearly all callers use this for. > > ... and what people should be using it for 🙂 > > > > > Secondly it provides an unusual debugging interface that allows for the > > traversal of page tables in a userland range of memory even for that memory > > which is not described by a VMA. > > > > This is highly unusual and it is far from certain that such page tables > > should even exist, but perhaps this is precisely why it is useful as a > > debugging mechanism. > > > > As a result, this is utilised by ptdump only. Historically, things were > > reversed - ptdump was the only user, and other parts of the kernel evolved > > to use the kernel page table walking here. > > > > Since we have some complicated and confusing locking rules for the novma > > case, it makes sense to separate the two usages into their own functions. > > > > Doing this also provide self-documentation as to the intent of the caller - > > are they doing something rather unusual or are they simply doing a standard > > kernel page table walk? > > > > We therefore maintain walk_page_range_novma() for this single usage, and > > document the function as such. > > If we have to keep this dangerous interface, it should probably be > > walk_page_range_debug() or walk_page_range_dump()
We can also move it from include/linux/pagewalk.h to mm/internal.h > > > > Note that ptdump uses the precise same function for kernel walking as a > > convenience, so we permit this but make it very explicit by having > > walk_page_range_novma() invoke walk_page_range_kernel() in this case. > > > > We introduce walk_page_range_kernel() for the far more common case of > > kernel page table traversal. > > I wonder if we should give it a completely different name scheme to > highlight that this is something completely different. > > walk_kernel_page_table_range() > > etc. > > > -- > Cheers, > > David / dhildenb > -- Sincerely yours, Mike.
