tools/mm: add script to display page state for a given PID and VADDR

Introduces a new drgn script, `show_page_info.py`, which allows users
to analyze the state of a page given a process ID (PID) and a virtual
address (VADDR). This can help kernel developers or debuggers easily
inspect page-related information in a live kernel or vmcore.

The script extracts information such as the page flags, mapping, and
other metadata relevant to diagnosing memory issues.

Output example:
sudo ./show_page_info.py 1 0x7fc988181000
PID: 1 Comm: systemd mm: 0xffff8d22c4089700
RAW: 0017ffffc000416c fffff939062ff708 fffff939062ffe08 ffff8d23062a12a8
RAW: 0000000000000000 ffff8d2323438f60 0000002500000007 ffff8d23203ff500
Page Address: 0xfffff93905664e00
Page Flags: PG_referenced|PG_uptodate|PG_lru|PG_head|PG_active|
PG_private|PG_reported|PG_has_hwpoisoned
Page Size: 4096
Page PFN: 0x159938
Page Physical: 0x159938000
Page Virtual: 0xffff8d2319938000
Page Refcount: 37
Page Mapcount: 7
Page Index: 0x0
Page Memcg Data: 0xffff8d23203ff500
Memcg Name: init.scope
Memcg Path: /sys/fs/cgroup/memory/init.scope
Page Mapping: 0xffff8d23062a12a8
Page Anon/File: File
Page VMA: 0xffff8d22e06e0e40
VMA Start: 0x7fc988181000
VMA End: 0x7fc988185000
This page is part of a compound page.
This page is the head page of a compound page.
Head Page: 0xfffff93905664e00
Compound Order: 2
Number of Pages: 4

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ye Liu <[e-mail]>
Tested-by: SeongJae Park <[e-mail]>
Reviewed-by: Stephen Brennan <[e-mail]>
Cc: Florian Weimer <[e-mail]>
Cc: Omar Sandoval <[e-mail]>
Cc: "Paul E . McKenney" <[e-mail]>
Cc: Sweet Tea Dorminy <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

MAINTAINERS

···
 F:	include/linux/page_table_check.h
 F:	mm/page_table_check.c
 
+PAGE STATE DEBUG SCRIPT
+M:	Ye Liu <[e-mail]>
+S:	Maintained
+F:	tools/mm/show_page_info.py
+
 PANASONIC LAPTOP ACPI EXTRAS DRIVER
 M:	Kenneth Chan <[e-mail]>
 L:	[e-mail]

tools/mm/show_page_info.py

···
+#!/usr/bin/env drgn
+# SPDX-License-Identifier: GPL-2.0-only
+# Copyright (C) 2025 Ye Liu <[e-mail]>
+
+import argparse
+import sys
+from drgn import Object, FaultError, PlatformFlags, cast
+from drgn.helpers.linux import find_task, follow_page, page_size
+from drgn.helpers.linux.mm import (
+    decode_page_flags, page_to_pfn, page_to_phys, page_to_virt, vma_find,
+    PageSlab, PageCompound, PageHead, PageTail, compound_head, compound_order, compound_nr
+)
+from drgn.helpers.linux.cgroup import cgroup_name, cgroup_path
+
+DESC = """
+This is a drgn script to show the page state.
+For more info on drgn, visit https://github.com/osandov/drgn.
+"""
+
+def format_page_data(page):
+    """
+    Format raw page data into a readable hex dump with "RAW:" prefix.
+
+    :param page: drgn.Object instance representing the page.
+    :return: Formatted string of memory contents.
+    """
+    try:
+        address = page.value_()
+        size = prog.type("struct page").size
+
+        if prog.platform.flags & PlatformFlags.IS_64_BIT:
+            word_size = 8
+        else:
+            word_size = 4
+        num_words = size // word_size
+
+        values = []
+        for i in range(num_words):
+            word_address = address + i * word_size
+            word = prog.read_word(word_address)
+            values.append(f"{word:0{word_size * 2}x}")
+
+        lines = [f"RAW: {' '.join(values[i:i + 4])}" for i in range(0, len(values), 4)]
+
+        return "\n".join(lines)
+
+    except FaultError as e:
+        return f"Error reading memory: {e}"
+    except Exception as e:
+        return f"Unexpected error: {e}"
+
+def get_memcg_info(page):
+    """Retrieve memory cgroup information for a page."""
+    try:
+        MEMCG_DATA_OBJEXTS = prog.constant("MEMCG_DATA_OBJEXTS").value_()
+        MEMCG_DATA_KMEM = prog.constant("MEMCG_DATA_KMEM").value_()
+        mask = prog.constant('__NR_MEMCG_DATA_FLAGS').value_() - 1
+        memcg_data = page.memcg_data.read_()
+        if memcg_data & MEMCG_DATA_OBJEXTS:
+            slabobj_ext = cast("struct slabobj_ext *", memcg_data & ~mask)
+            memcg = slabobj_ext.objcg.memcg.value_()
+        elif memcg_data & MEMCG_DATA_KMEM:
+            objcg = cast("struct obj_cgroup *", memcg_data & ~mask)
+            memcg = objcg.memcg.value_()
+        else:
+            memcg = cast("struct mem_cgroup *", memcg_data & ~mask)
+
+        if memcg.value_() == 0:
+            return "none", "/sys/fs/cgroup/memory/"
+        cgrp = memcg.css.cgroup
+        return cgroup_name(cgrp).decode(), f"/sys/fs/cgroup/memory{cgroup_path(cgrp).decode()}"
+    except FaultError as e:
+        return "unknown", f"Error retrieving memcg info: {e}"
+    except Exception as e:
+        return "unknown", f"Unexpected error: {e}"
+
+def show_page_state(page, addr, mm, pid, task):
+    """Display detailed information about a page."""
+    try:
+        print(f'PID: {pid} Comm: {task.comm.string_().decode()} mm: {hex(mm)}')
+        try:
+            print(format_page_data(page))
+        except FaultError as e:
+            print(f"Error reading page data: {e}")
+        fields = {
+            "Page Address": hex(page.value_()),
+            "Page Flags": decode_page_flags(page),
+            "Page Size": prog["PAGE_SIZE"].value_(),
+            "Page PFN": hex(page_to_pfn(page).value_()),
+            "Page Physical": hex(page_to_phys(page).value_()),
+            "Page Virtual": hex(page_to_virt(page).value_()),
+            "Page Refcount": page._refcount.counter.value_(),
+            "Page Mapcount": page._mapcount.counter.value_(),
+            "Page Index": hex(page.__folio_index.value_()),
+            "Page Memcg Data": hex(page.memcg_data.value_()),
+        }
+
+        memcg_name, memcg_path = get_memcg_info(page)
+        fields["Memcg Name"] = memcg_name
+        fields["Memcg Path"] = memcg_path
+        fields["Page Mapping"] = hex(page.mapping.value_())
+        fields["Page Anon/File"] = "Anon" if page.mapping.value_() & 0x1 else "File"
+
+        try:
+            vma = vma_find(mm, addr)
+            fields["Page VMA"] = hex(vma.value_())
+            fields["VMA Start"] = hex(vma.vm_start.value_())
+            fields["VMA End"] = hex(vma.vm_end.value_())
+        except FaultError as e:
+            fields["Page VMA"] = "Unavailable"
+            fields["VMA Start"] = "Unavailable"
+            fields["VMA End"] = "Unavailable"
+            print(f"Error retrieving VMA information: {e}")
+
+        # Calculate the maximum field name length for alignment
+        max_field_len = max(len(field) for field in fields)
+
+        # Print aligned fields
+        for field, value in fields.items():
+            print(f"{field}:".ljust(max_field_len + 2) + f"{value}")
+
+        # Additional information about the page
+        if PageSlab(page):
+            print("This page belongs to the slab allocator.")
+
+        if PageCompound(page):
+            print("This page is part of a compound page.")
+            if PageHead(page):
+                print("This page is the head page of a compound page.")
+            if PageTail(page):
+                print("This page is the tail page of a compound page.")
+            print(f"{'Head Page:'.ljust(max_field_len + 2)}{hex(compound_head(page).value_())}")
+            print(f"{'Compound Order:'.ljust(max_field_len + 2)}{compound_order(page).value_()}")
+            print(f"{'Number of Pages:'.ljust(max_field_len + 2)}{compound_nr(page).value_()}")
+        else:
+            print("This page is not part of a compound page.")
+    except FaultError as e:
+        print(f"Error accessing page state: {e}")
+    except Exception as e:
+        print(f"Unexpected error: {e}")
+
+def main():
+    """Main function to parse arguments and display page state."""
+    parser = argparse.ArgumentParser(description=DESC, formatter_class=argparse.RawTextHelpFormatter)
+    parser.add_argument('pid', metavar='PID', type=int, help='Target process ID (PID)')
+    parser.add_argument('vaddr', metavar='VADDR', type=str, help='Target virtual address in hexadecimal format (e.g., 0x7fff1234abcd)')
+    args = parser.parse_args()
+
+    try:
+        vaddr = int(args.vaddr, 16)
+    except ValueError:
+        sys.exit(f"Error: Invalid virtual address format: {args.vaddr}")
+
+    try:
+        task = find_task(args.pid)
+        mm = task.mm
+        page = follow_page(mm, vaddr)
+
+        if page:
+            show_page_state(page, vaddr, mm, args.pid, task)
+        else:
+            sys.exit(f"Address {hex(vaddr)} is not mapped.")
+    except FaultError as e:
+        sys.exit(f"Error accessing task or memory: {e}")
+    except Exception as e:
+        sys.exit(f"Unexpected error: {e}")
+
+if __name__ == "__main__":
+    main()