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Message-ID: <16280f8e-31c9-7b0b-b0c1-4d180c4d0045@siemens.com>
Date: Mon, 2 Jan 2023 09:59:35 +0100
From: Jan Kiszka <jan.kiszka@...mens.com>
To: Dmitrii Bundin <dmitrii.bundin.a@...il.com>, rppt@...nel.org
Cc: akpm@...ux-foundation.org, gregkh@...uxfoundation.org,
kbingham@...nel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, mingo@...hat.com, vbabka@...e.cz,
x86@...nel.org
Subject: Re: [PATCH v3] scripts/gdb: add mm introspection utils
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@...il.com>
> ---
>
> Changes in v2: https://lore.kernel.org/all/20221230163512.23736-1-dmitrii.bundin.a@gmail.com/
> - 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@gmail.com/
> - 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@...il.com>
> +#
> +# 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
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