[PATCH v4] scripts/gdb: add mm introspection utils

[Dmitrii Bundin]

This command provides a way to traverse the entire page hierarchy by a
given virtual address on x86. In addition to qemu's commands info
tlb/info mem it provides the complete information about the paging
structure for an arbitrary virtual address. It supports 4KB/2MB/1GB and
5 level paging.

Here is an example output for 2MB success translation:

(gdb) translate-vm address
cr3:
    cr3 binary data                0x10a1f8004
    next entry physicall address   0x10a1f8000
    ---
    bit  3          page level write through       False
    bit  4          page level cache disabled      False
level 4:
    entry address                  0xffff88810a1f87f0
    page entry binary data         0x8000000109042067
    next entry physicall address   0x109042000
    ---
    bit  0          entry present                  True
    bit  1          read/write access allowed      True
    bit  2          user access allowed            True
    bit  3          page level write through       False
    bit  4          page level cache disabled      False
    bit  5          entry has been accessed        True
    bit  7          page size                      False
    bit  11         restart to ordinary            False
    bit  63         execute disable                True
level 3:
    entry address                  0xffff888109042e40
    page entry binary data         0x10ec93067
    next entry physicall address   0x10ec93000
    ---
    bit  0          entry present                  True
    bit  1          read/write access allowed      True
    bit  2          user access allowed            True
    bit  3          page level write through       False
    bit  4          page level cache disabled      False
    bit  5          entry has been accessed        True
    bit  7          page size                      False
    bit  11         restart to ordinary            False
    bit  63         execute disable                False
level 2:
    entry address                  0xffff88810ec939a8
    page entry binary data         0x800000012b6008e7
    page size                      2MB
    page physicall address         0x12b600000
    ---
    bit  0          entry present                  True
    bit  1          read/write access allowed      True
    bit  2          user access allowed            True
    bit  3          page level write through       False
    bit  4          page level cache disabled      False
    bit  5          entry has been accessed        True
    bit  6          page dirty                     True
    bit  7          page size                      True
    bit  8          global translation             False
    bit  11         restart to ordinary            True
    bit  12         pat                            False
    bits (59, 62)   protection key                 0
    bit  63         execute disable                True

Signed-off-by: Dmitrii Bundin <dmitrii.bundin.a@xxxxxxxxx>
---

Changes in v2: https://lore.kernel.org/all/20221230163512.23736-1-dmitrii.bundin.a@xxxxxxxxx/
    - Fix commit message to mention x86 explicitly
    - Assign page_offset_base to a constant in case
      CONFIG_DYNAMIC_MEMORY_LAYOUT is disabled

Changes in v3: https://lore.kernel.org/all/20221231171258.7907-1-dmitrii.bundin.a@xxxxxxxxx/
    - Make debug output lower case and column aligned

Changes in v4: https://lore.kernel.org/all/20230101172312.21452-1-dmitrii.bundin.a@xxxxxxxxx/
    - Added currently supported archs in the command help
    - Remove excessive newline

 scripts/gdb/linux/mm.py    | 223 +++++++++++++++++++++++++++++++++++++
 scripts/gdb/vmlinux-gdb.py |   1 +
 2 files changed, 224 insertions(+)
 create mode 100644 scripts/gdb/linux/mm.py

diff --git a/scripts/gdb/linux/mm.py b/scripts/gdb/linux/mm.py
new file mode 100644
index 000000000000..2a0b6cb6a1f8
--- /dev/null
+++ b/scripts/gdb/linux/mm.py
@@ -0,0 +1,223 @@
+#
+# gdb helper commands and functions for Linux kernel debugging
+#
+#  routines to introspect page table
+#
+# Authors:
+#  Dmitrii Bundin <dmitrii.bundin.a@xxxxxxxxx>
+#
+# This work is licensed under the terms of the GNU GPL version 2.
+#
+
+import gdb
+
+from linux import utils
+
+PHYSICAL_ADDRESS_MASK = gdb.parse_and_eval('0xfffffffffffff')
+
+
+def page_mask(level=1):
+    # 4KB
+    if level == 1:
+        return gdb.parse_and_eval('(u64) ~0xfff')
+    # 2MB
+    elif level == 2:
+        return gdb.parse_and_eval('(u64) ~0x1fffff')
+    # 1GB
+    elif level == 3:
+        return gdb.parse_and_eval('(u64) ~0x3fffffff')
+    else:
+        raise Exception(f'Unknown page level: {level}')
+
+
+#page_offset_base in case CONFIG_DYNAMIC_MEMORY_LAYOUT is disabled
+POB_NO_DYNAMIC_MEM_LAYOUT = '0xffff888000000000'
+def _page_offset_base():
+    pob_symbol = gdb.lookup_global_symbol('page_offset_base')
+    pob = pob_symbol.name if pob_symbol else POB_NO_DYNAMIC_MEM_LAYOUT
+    return gdb.parse_and_eval(pob)
+
+
+def is_bit_defined_tupled(data, offset):
+    return offset, bool(data >> offset & 1)
+
+def content_tupled(data, bit_start, bit_end):
+    return (bit_start, bit_end), data >> bit_start & ((1 << (1 + bit_end - bit_start)) - 1)
+
+def entry_va(level, phys_addr, translating_va):
+        def start_bit(level):
+            if level == 5:
+                return 48
+            elif level == 4:
+                return 39
+            elif level == 3:
+                return 30
+            elif level == 2:
+                return 21
+            elif level == 1:
+                return 12
+            else:
+                raise Exception(f'Unknown level {level}')
+
+        entry_offset =  ((translating_va >> start_bit(level)) & 511) * 8
+        entry_va = _page_offset_base() + phys_addr + entry_offset
+        return entry_va
+
+class Cr3():
+    def __init__(self, cr3, page_levels):
+        self.cr3 = cr3
+        self.page_levels = page_levels
+        self.page_level_write_through = is_bit_defined_tupled(cr3, 3)
+        self.page_level_cache_disabled = is_bit_defined_tupled(cr3, 4)
+        self.next_entry_physical_address = cr3 & PHYSICAL_ADDRESS_MASK & page_mask()
+
+    def next_entry(self, va):
+        next_level = self.page_levels
+        return PageHierarchyEntry(entry_va(next_level, self.next_entry_physical_address, va), next_level)
+
+    def mk_string(self):
+            return f"""\
+cr3:
+    {'cr3 binary data': <30} {hex(self.cr3)}
+    {'next entry physicall address': <30} {hex(self.next_entry_physical_address)}
+    ---
+    {'bit' : <4} {self.page_level_write_through[0]: <10} {'page level write through': <30} {self.page_level_write_through[1]}
+    {'bit' : <4} {self.page_level_cache_disabled[0]: <10} {'page level cache disabled': <30} {self.page_level_cache_disabled[1]}
+"""
+
+
+class PageHierarchyEntry():
+    def __init__(self, address, level):
+        data = int.from_bytes(
+            memoryview(gdb.selected_inferior().read_memory(address, 8)),
+            "little"
+        )
+        if level == 1:
+            self.is_page = True
+            self.entry_present = is_bit_defined_tupled(data, 0)
+            self.read_write = is_bit_defined_tupled(data, 1)
+            self.user_access_allowed = is_bit_defined_tupled(data, 2)
+            self.page_level_write_through = is_bit_defined_tupled(data, 3)
+            self.page_level_cache_disabled = is_bit_defined_tupled(data, 4)
+            self.entry_was_accessed = is_bit_defined_tupled(data, 5)
+            self.dirty = is_bit_defined_tupled(data, 6)
+            self.pat = is_bit_defined_tupled(data, 7)
+            self.global_translation = is_bit_defined_tupled(data, 8)
+            self.page_physical_address = data & PHYSICAL_ADDRESS_MASK & page_mask(level)
+            self.next_entry_physical_address = None
+            self.hlat_restart_with_ordinary = is_bit_defined_tupled(data, 11)
+            self.protection_key = content_tupled(data, 59, 62)
+            self.executed_disable = is_bit_defined_tupled(data, 63)
+        else:
+            page_size = is_bit_defined_tupled(data, 7)
+            page_size_bit = page_size[1]
+            self.is_page = page_size_bit
+            self.entry_present = is_bit_defined_tupled(data, 0)
+            self.read_write = is_bit_defined_tupled(data, 1)
+            self.user_access_allowed = is_bit_defined_tupled(data, 2)
+            self.page_level_write_through = is_bit_defined_tupled(data, 3)
+            self.page_level_cache_disabled = is_bit_defined_tupled(data, 4)
+            self.entry_was_accessed = is_bit_defined_tupled(data, 5)
+            self.page_size = page_size
+            self.dirty = is_bit_defined_tupled(
+                data, 6) if page_size_bit else None
+            self.global_translation = is_bit_defined_tupled(
+                data, 8) if page_size_bit else None
+            self.pat = is_bit_defined_tupled(
+                data, 12) if page_size_bit else None
+            self.page_physical_address = data & PHYSICAL_ADDRESS_MASK & page_mask(level) if page_size_bit else None
+            self.next_entry_physical_address = None if page_size_bit else data & PHYSICAL_ADDRESS_MASK & page_mask()
+            self.hlat_restart_with_ordinary = is_bit_defined_tupled(data, 11)
+            self.protection_key = content_tupled(data, 59, 62) if page_size_bit else None
+            self.executed_disable = is_bit_defined_tupled(data, 63)
+        self.address = address
+        self.page_entry_binary_data = data
+        self.page_hierarchy_level = level
+
+    def next_entry(self, va):
+        if self.is_page or not self.entry_present[1]:
+            return None
+
+        next_level = self.page_hierarchy_level - 1
+        return PageHierarchyEntry(entry_va(next_level, self.next_entry_physical_address, va), next_level)
+
+
+    def mk_string(self):
+        if not self.entry_present[1]:
+            return f"""\
+level {self.page_hierarchy_level}:
+    {'entry address': <30} {hex(self.address)}
+    {'page entry binary data': <30} {hex(self.page_entry_binary_data)}
+    ---
+    PAGE ENTRY IS NOT PRESENT!
+"""
+        elif self.is_page:
+            def page_size_line(ps_bit, ps, level):
+                return "" if level == 1 else f"{'bit': <3} {ps_bit: <5} {'page size': <30} {ps}"
+
+            return f"""\
+level {self.page_hierarchy_level}:
+    {'entry address': <30} {hex(self.address)}
+    {'page entry binary data': <30} {hex(self.page_entry_binary_data)}
+    {'page size': <30} {'1GB' if self.page_hierarchy_level == 3 else '2MB' if self.page_hierarchy_level == 2 else '4KB' if self.page_hierarchy_level == 1 else 'Unknown page size for level:' + self.page_hierarchy_level}
+    {'page physicall address': <30} {hex(self.page_physical_address)}
+    ---
+    {'bit': <4} {self.entry_present[0]: <10} {'entry present': <30} {self.entry_present[1]}
+    {'bit': <4} {self.read_write[0]: <10} {'read/write access allowed': <30} {self.read_write[1]}
+    {'bit': <4} {self.user_access_allowed[0]: <10} {'user access allowed': <30} {self.user_access_allowed[1]}
+    {'bit': <4} {self.page_level_write_through[0]: <10} {'page level write through': <30} {self.page_level_write_through[1]}
+    {'bit': <4} {self.page_level_cache_disabled[0]: <10} {'page level cache disabled': <30} {self.page_level_cache_disabled[1]}
+    {'bit': <4} {self.entry_was_accessed[0]: <10} {'entry has been accessed': <30} {self.entry_was_accessed[1]}
+    {"" if self.page_hierarchy_level == 1 else f"{'bit': <4} {self.page_size[0]: <10} {'page size': <30} {self.page_size[1]}"}
+    {'bit': <4} {self.dirty[0]: <10} {'page dirty': <30} {self.dirty[1]}
+    {'bit': <4} {self.global_translation[0]: <10} {'global translation': <30} {self.global_translation[1]}
+    {'bit': <4} {self.hlat_restart_with_ordinary[0]: <10} {'restart to ordinary': <30} {self.hlat_restart_with_ordinary[1]}
+    {'bit': <4} {self.pat[0]: <10} {'pat': <30} {self.pat[1]}
+    {'bits': <4} {str(self.protection_key[0]): <10} {'protection key': <30} {self.protection_key[1]}
+    {'bit': <4} {self.executed_disable[0]: <10} {'execute disable': <30} {self.executed_disable[1]}
+"""
+        else:
+            return f"""\
+level {self.page_hierarchy_level}:
+    {'entry address': <30} {hex(self.address)}
+    {'page entry binary data': <30} {hex(self.page_entry_binary_data)}
+    {'next entry physicall address': <30} {hex(self.next_entry_physical_address)}
+    ---
+    {'bit': <4} {self.entry_present[0]: <10} {'entry present': <30} {self.entry_present[1]}
+    {'bit': <4} {self.read_write[0]: <10} {'read/write access allowed': <30} {self.read_write[1]}
+    {'bit': <4} {self.user_access_allowed[0]: <10} {'user access allowed': <30} {self.user_access_allowed[1]}
+    {'bit': <4} {self.page_level_write_through[0]: <10} {'page level write through': <30} {self.page_level_write_through[1]}
+    {'bit': <4} {self.page_level_cache_disabled[0]: <10} {'page level cache disabled': <30} {self.page_level_cache_disabled[1]}
+    {'bit': <4} {self.entry_was_accessed[0]: <10} {'entry has been accessed': <30} {self.entry_was_accessed[1]}
+    {'bit': <4} {self.page_size[0]: <10} {'page size': <30} {self.page_size[1]}
+    {'bit': <4} {self.hlat_restart_with_ordinary[0]: <10} {'restart to ordinary': <30} {self.hlat_restart_with_ordinary[1]}
+    {'bit': <4} {self.executed_disable[0]: <10} {'execute disable': <30} {self.executed_disable[1]}
+"""
+
+
+class TranslateVM(gdb.Command):
+    """Prints the entire paging structure used to translate a given virtual address.
+
+Having an address space of the currently executed process translates the virtual address
+and prints detailed information of all paging structure levels used for the transaltion.
+Currently supported arch: x86"""
+
+    def __init__(self):
+        super(TranslateVM, self).__init__('translate-vm', gdb.COMMAND_USER)
+
+    def invoke(self, arg, from_tty):
+        if utils.is_target_arch("x86"):
+            vm_address = gdb.parse_and_eval(f'{arg}')
+            cr3_data = gdb.parse_and_eval('$cr3')
+            cr4 = gdb.parse_and_eval('$cr4')
+            page_levels = 5 if cr4 & (1 << 12) else 4
+            page_entry = Cr3(cr3_data, page_levels)
+            while page_entry:
+                gdb.write(page_entry.mk_string())
+                page_entry = page_entry.next_entry(vm_address)
+        else:
+            gdb.GdbError("Virtual address translation is not"
+                         "supported for this arch")
+
+
+TranslateVM()
diff --git a/scripts/gdb/vmlinux-gdb.py b/scripts/gdb/vmlinux-gdb.py
index 4136dc2c59df..27bd7339bccc 100644
--- a/scripts/gdb/vmlinux-gdb.py
+++ b/scripts/gdb/vmlinux-gdb.py
@@ -37,3 +37,4 @@ else:
     import linux.clk
     import linux.genpd
     import linux.device
+    import linux.mm
-- 
2.17.1