Re: [PATCH v3] scripts/gdb: add mm introspection utils

[Jan Kiszka]

On 01.01.23 18:23, Dmitrii Bundin wrote:
> 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
> 
>  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..7bfe39f32b7c
> --- /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."""
> +

Either the help text should make clear which archs are supported...

> +    def __init__(self):
> +        super(TranslateVM, self).__init__('translate-vm', gdb.COMMAND_USER)

...or you do not even add the command for unsupported ones.

> +
> +    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")
> +
> +
> +

One blank line too much, I would say.

> +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

Looks indeed useful, and I suspect support for other archs will follow.

Jan

-- 
Siemens AG, Technology
Competence Center Embedded Linux