Backport subject : "Improve PTDUMP and introduce new fields"

[cp0613]

commit: https://lore.kernel.org/all/20230921025022.3989723-1-peterlin@andestech.com/

This patchset enhances PTDUMP by providing additional information from pagetable entries.

The first patch fixes the RSW field, while the second and third patches introduce the PBMT and NAPOT fields, respectively, for RV64 systems.

PR: #206

[cp0613]

The ptdump (page table dump) feature in the Linux kernel prints the virtual memory page table structure, helping developers visualize address mappings, verify memory permissions, and debug issues like page faults or incorrect translations—especially useful during kernel bring-up and memory subsystem debugging.

[cp0613]

The original RISC-V ptdump implementation does not include the PBMT and NAPOT fields, which are memory attributes for NC, IO, or N. This series of patches enhances this information.

The testing methodology can be found at https://docs.kernel.org/arch/arm64/ptdump.html as follows:

CONFIG_PTDUMP_DEBUGFS=y

mount -t debugfs nodev /sys/kernel/debug
cat /sys/kernel/debug/kernel_page_tables

Before enhancement:

# mount -t debugfs nodev /sys/kernel/debug
# cat /sys/kernel/debug/kernel_page_tables
---[ Fixmap start ]---
0xffff8b7ffec00000-0xffff8b7fff000000    0x00000000bfe00000         4M PMD     D A G . . W R V
---[ Fixmap end ]---
---[ PCI I/O start ]---
0xffff8b7fff000000-0xffff8b7fff010000    0x0000000003000000        64K PTE     D A G . . W R V

After enhancement:

# mount -t debugfs nodev /sys/kernel/debug
# cat /sys/kernel/debug/kernel_page_tables
---[ Fixmap start ]---
0xffff8b7ffec00000-0xffff8b7fff000000    0x00000000bfe00000         4M PMD .   ..     ..   D A G . . W R V
---[ Fixmap end ]---
---[ PCI I/O start ]---
0xffff8b7fff000000-0xffff8b7fff010000    0x0000000003000000        64K PTE . MT(IO)   ..   D A G . . W R V