On 6/4/25 10:19 PM, 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. 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. 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 establish two separate functions - walk_page_range_debug() for this single usage, and walk_kernel_page_table_range() for general kernel page table walking. We additionally make walk_page_range_debug() internal to mm. 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_kernel_page_table_range() in this case. Signed-off-by: Lorenzo Stoakes <lorenzo.stoa...@oracle.com> Acked-by: Mike Rapoport (Microsoft) <r...@kernel.org> --- v2: * Renamed walk_page_range_novma() to walk_page_range_debug() as per David. * Moved walk_page_range_debug() definition to mm/internal.h as per Mike. * Renamed walk_page_range_kernel() to walk_kernel_page_table_range() as per David. v1 resend: * Actually cc'd lists... * Fixed mistake in walk_page_range_novma() not handling kernel mappings and update commit message to referene. * Added Mike's off-list Acked-by. * Fixed up comments as per Mike. * Add some historic flavour to the commit message as per Mike. https://lore.kernel.org/all/20250603192213.182931-1-lorenzo.stoa...@oracle.com/ v1: (accidentally sent off-list due to error in scripting) arch/loongarch/mm/pageattr.c | 2 +- arch/openrisc/kernel/dma.c | 4 +- arch/riscv/mm/pageattr.c | 8 +-- include/linux/pagewalk.h | 7 ++- mm/hugetlb_vmemmap.c | 2 +- mm/internal.h | 4 ++ mm/pagewalk.c | 98 ++++++++++++++++++++++++------------ mm/ptdump.c | 3 +- 8 files changed, 82 insertions(+), 46 deletions(-)
Acked-by: Qi Zheng <zhengqi.a...@bytedance.com> Thanks.
