[PATCH v6 0/6] arm64: ptdump: View the second stage page-tables

[Sebastian Ene]

Hi,

This is the first part of the series which enables dumping of the guest
stage-2 pagetables. The support for dumping the host stage-2 pagetables
which is pKVM specific will be part of a follow-up series as per the
feedback received in v4. 

When CONFIG_PTDUMP_STAGE2_DEBUGFS is enabled, ptdump registers 
'/sys/debug/kvm/<guest_id>/stage2_page_tables' entry with debugfs
upon guest creation. This allows userspace tools (eg. cat) to dump the
stage-2 pagetables by reading the registered file.

Reading the debugfs file shows stage-2 memory ranges in following format:
<IPA range> <size> <descriptor type> <access permissions> <mem_attributes>

Below is the output of a guest stage-2 pagetable mappings running under
Qemu:

---[ IPA bits 33 start lvl 2 ]---
0x0000000000000000-0x0000000080000000           2G PGD
0x0000000080000000-0x0000000080c00000          12M PGD      R W AF        BLK
0x0000000080c00000-0x0000000080e00000           2M PGD   XN R W AF        BLK
0x0000000080e00000-0x0000000081000000           2M PGD      R W AF        BLK
0x0000000081000000-0x0000000081400000           4M PGD   XN R W AF        BLK
0x0000000081400000-0x000000008fe00000         234M PGD
0x000000008fe00000-0x0000000090000000           2M PGD   XN R W AF        BLK
0x0000000090000000-0x00000000fa000000        1696M PGD
0x00000000fa000000-0x00000000fe000000          64M PGD   XN R W AF        BLK
0x00000000fe000000-0x0000000100000000          32M PGD
0x0000000100000000-0x0000000101c00000          28M PGD   XN R W AF        BLK
0x0000000101c00000-0x0000000102000000           4M PGD
0x0000000102000000-0x0000000102200000           2M PGD   XN R W AF        BLK
0x0000000102200000-0x000000017b000000        1934M PGD
0x000000017b000000-0x0000000180000000          80M PGD   XN R W AF        BLK

Link to v5:
https://lore.kernel.org/all/20240207144832.1017815-2-sebastianene@google.com/

Link to v4:
https://lore.kernel.org/all/20231218135859.2513568-2-sebastianene@google.com/

Link to v3:
https://lore.kernel.org/all/20231115171639.2852644-2-sebastianene@google.com/

Changelog:
 v5 -> current:
 * don't return an error if the kvm_arch_create_vm_debugfs fails to
   initialize (ref.
https://lore.kernel.org/all/20240216155941.2029458-1-oliver.upton@linux.dev/)  
 * fix use-after-free suggested by getting a reference to the
   KVM struct while manipulating the debugfs files
   and put the reference on the file close.
 * do all the allocations at once for the ptdump parser state tracking
   and simplify the initialization.
 * move the ptdump parser state initialization as part of the file_open
 * create separate files for printing the guest stage-2 pagetable
   configuration such as: the start level of the pagetable walk and the
   number of bits used for the IPA space representation.
 * fixed the wrong header format for the newly added file
 * include missing patch which hasn't been posted on the v5:
   "KVM-arm64-Move-pagetable-definitions-to-common-heade.patch" 


 v4 -> v5:
 * refactorization: split the series into two parts as per the feedback
   received from Oliver. Introduce the base support which allows dumping
   of the guest stage-2 pagetables.
 
 * removed the *ops* struct wrapper built on top of the file_ops and
   simplify the ptdump interface access.
 
 * keep the page table walker away from the ptdump specific code

  v3 -> current_version:
  * refactorization: moved all the **KVM** specific components under
    kvm/ as suggested by Oliver. Introduced a new file
    arm64/kvm/ptdump.c which handled the second stage translation.
    re-used only the display portion from mm/ptdump.c

  * pagetable snapshot creation now uses memory donated from the host.
    The memory is no longer shared with the host as this can pose a security
    risk if the host has access to manipulate the pagetable copy while
    the hypervisor iterates it.

  * fixed a memory leak: while memory was used from the memcache for
    building the snapshot pagetable, it was no longer giving back the
    pages to the host for freeing. A separate array was introduced to
    keep track of the pages allocated from the memcache.


  v2 -> v3:
  * register the stage-2 debugfs entry for the host under
    /sys/debug/kvm/host_stage2_page_tables and in
    /sys/debug/kvm/<guest_id>/stage2_page_tables for guests.

  * don't use a static array for parsing the attributes description,
    generate it dynamically based on the number of pagetable levels

  * remove the lock that was guarding the seq_file private inode data,
    and keep the data private to the open file session.

  * minor fixes & renaming of CONFIG_NVHE_EL2_PTDUMP_DEBUGFS to
    CONFIG_PTDUMP_STAGE2_DEBUGFS


  v1 -> v2:
  * use the stage-2 pagetable walker for dumping descriptors instead of
    the one provided by ptdump.

  * support for guests pagetables dumping under VHE/nVHE non-protected

Thanks,

Sebastian Ene (6):
  KVM: arm64: Move pagetable definitions to common header
  arm64: ptdump: Expose the attribute parsing functionality
  arm64: ptdump: Use the mask from the state structure
  KVM: arm64: Register ptdump with debugfs on guest creation
  KVM: arm64: Initialize the ptdump parser with stage-2 attributes
  KVM: arm64: Expose guest stage-2 pagetable config to debugfs

 arch/arm64/include/asm/kvm_pgtable.h |  42 +++++
 arch/arm64/include/asm/ptdump.h      |  42 ++++-
 arch/arm64/kvm/Kconfig               |  13 ++
 arch/arm64/kvm/Makefile              |   1 +
 arch/arm64/kvm/debug.c               |   8 +
 arch/arm64/kvm/hyp/pgtable.c         |  42 -----
 arch/arm64/kvm/kvm_ptdump.h          |  20 ++
 arch/arm64/kvm/ptdump.c              | 270 +++++++++++++++++++++++++++
 arch/arm64/mm/ptdump.c               |  49 +----
 9 files changed, 405 insertions(+), 82 deletions(-)
 create mode 100644 arch/arm64/kvm/kvm_ptdump.h
 create mode 100644 arch/arm64/kvm/ptdump.c

-- 
2.44.0.rc0.258.g7320e95886-goog