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android-kvm / linux / refs/heads/for-android/pkvm-coalescing
commit4335938aa6415dc9f39bed6189c7ef5dd6296c2a[log] [tgz]
authorSebastian Ene <sebastianene@google.com>Wed Jul 26 11:40:03 2023 +0000
committerKeir Fraser <keirf@google.com>Tue Sep 10 07:30:40 2024 +0000
tree462eb9aeb3fb80c7793f9e1dda2d81980941946f
parent08fe78b8918220441014c33414bd5e96a6e6fb5c [diff]
KVM: arm64: Coalesce host stage2 entries on ownership reclaim

This optimization allows us to re-create higher order block mappings in
the host stage2 pagetables after we teardown a guest VM. The coalescing
code is triggered on host_stage2_set_owner_locked path when we annotate
the entries in the host stage2 page-tables with an invalid entry that has
the owner set to PKVM_ID_HOST. This can also be triggered from
page_relinquish when we do page insertion in the ballooning code.

This patch reintroduces the _post callback walker to be able to zap the
page table entries on ownership re-assignment.

When the host reclaims ownership during guest teardown, the page table
walker drops the refcount of the counted entries and clears out
unreferenced entries (refcount == 1). Clearing out the entry installs a
zero PTE. When the host stage2 receives a data abort because there is no
mapping associated, it will try to create the largest possible block
mapping from the founded leaf entry.
With the current patch, we increase the chances of finding a leaf entry
that has level < 3 if the requested region comes from a reclaimed torned
down VM memory. This has the advantage of reducing the TLB pressure at
host stage2.

To be able to do coalescing, we modify the way we do refcounting by not
counting the following descriptor types at host stage 2:
- non-zero invalid PTEs
- any descriptor that has at least one of the reserved-high bits(58-55)
toogled
- non-default attribute mappings
- page table descriptors

The algorithm works as presented below:

  Is refcount(child(pte_table)) == 1 ?

  Yes -> (because we left only default mappings)
	Zap the table by setting 0 in the pte_table
	and put the page that holds the level 3 entries
	back into the memcache

  level 2
+---------+
|         |
|  ...    |
| pte_table---+      level 3      -> we can now re-create a 2Mb mapping
|  ...    |   +---> +---------+
|         |         |         |
|         |         |         |
|         |         |def entry|
+---------+         |         |
                    |def entry|
                    |         |
                    |  ...    |
                    +---------+

Change-Id: I983372a0fac876336ee6799be1f3c4a50015880c
Signed-off-by: Sebastian Ene <sebastianene@google.com>
3 files changed
tree: 462eb9aeb3fb80c7793f9e1dda2d81980941946f
  1. arch/
  2. block/
  3. certs/
  4. crypto/
  5. Documentation/
  6. drivers/
  7. fs/
  8. include/
  9. init/
  10. io_uring/
  11. ipc/
  12. kernel/
  13. lib/
  14. LICENSES/
  15. mm/
  16. net/
  17. rust/
  18. samples/
  19. scripts/
  20. security/
  21. sound/
  22. tools/
  23. usr/
  24. virt/
  25. .clang-format
  26. .cocciconfig
  27. .editorconfig
  28. .get_maintainer.ignore
  29. .gitattributes
  30. .gitignore
  31. .mailmap
  32. .rustfmt.toml
  33. abi.bzl
  34. BUILD.bazel
  35. build.config.aarch64
  36. build.config.allmodconfig
  37. build.config.allmodconfig.aarch64
  38. build.config.allmodconfig.arm
  39. build.config.allmodconfig.x86_64
  40. build.config.amlogic
  41. build.config.arm
  42. build.config.common
  43. build.config.constants
  44. build.config.crashdump
  45. build.config.crashdump.aarch64
  46. build.config.crashdump.x86_64
  47. build.config.db845c
  48. build.config.gki
  49. build.config.gki.aarch64
  50. build.config.gki.x86_64
  51. build.config.gki_kasan
  52. build.config.gki_kasan.aarch64
  53. build.config.gki_kasan.x86_64
  54. build.config.gki_kprobes
  55. build.config.gki_kprobes.aarch64
  56. build.config.gki_kprobes.x86_64
  57. build.config.khwasan
  58. build.config.kunit.aarch64
  59. build.config.kunit.x86_64
  60. build.config.microdroid
  61. build.config.microdroid.aarch64
  62. build.config.microdroid.x86_64
  63. build.config.rockpi4
  64. build.config.x86_64
  65. COPYING
  66. CREDITS
  67. Kbuild
  68. Kconfig
  69. Kconfig.ext
  70. MAINTAINERS
  71. Makefile
  72. modules.bzl
  73. OWNERS
  74. OWNERS_DrNo
  75. README
  76. README.md
README.md

How do I submit patches to Android Common Kernels

  1. BEST: Make all of your changes to upstream Linux. If appropriate, backport to the stable releases. These patches will be merged automatically in the corresponding common kernels. If the patch is already in upstream Linux, post a backport of the patch that conforms to the patch requirements below.

    • Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux, additions of EXPORT_SYMBOL_GPL() require an in-tree modular driver that uses the symbol -- so include the new driver or changes to an existing driver in the same patchset as the export.
    • When sending patches upstream, the commit message must contain a clear case for why the patch is needed and beneficial to the community. Enabling out-of-tree drivers or functionality is not a persuasive case.

  2. LESS GOOD: Develop your patches out-of-tree (from an upstream Linux point-of-view). Unless these are fixing an Android-specific bug, these are very unlikely to be accepted unless they have been coordinated with kernel-team@android.com. If you want to proceed, post a patch that conforms to the patch requirements below.

Common Kernel patch requirements

  • All patches must conform to the Linux kernel coding standards and pass scripts/checkpatch.pl
  • Patches shall not break gki_defconfig or allmodconfig builds for arm, arm64, x86, x86_64 architectures (see https://source.android.com/setup/build/building-kernels)
  • If the patch is not merged from an upstream branch, the subject must be tagged with the type of patch: UPSTREAM:, BACKPORT:, FROMGIT:, FROMLIST:, or ANDROID:.
  • All patches must have a Change-Id: tag (see https://gerrit-review.googlesource.com/Documentation/user-changeid.html)
  • If an Android bug has been assigned, there must be a Bug: tag.
  • All patches must have a Signed-off-by: tag by the author and the submitter

Additional requirements are listed below based on patch type

Requirements for backports from mainline Linux: UPSTREAM:, BACKPORT:

  • If the patch is a cherry-pick from Linux mainline with no changes at all
    • tag the patch subject with UPSTREAM:.
    • add upstream commit information with a (cherry picked from commit ...) line
    • Example:
      • if the upstream commit message is
        important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>
  • then Joe Smith would upload the patch for the common kernel as
        UPSTREAM: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch requires any changes from the upstream version, tag the patch with BACKPORT: instead of UPSTREAM:.
    • use the same tags as UPSTREAM:
    • add comments about the changes under the (cherry picked from commit ...) line
    • Example:
        BACKPORT: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
        [joe: Resolved minor conflict in drivers/foo/bar.c ]
        Signed-off-by: Joe Smith <joe.smith@foo.org>

Requirements for other backports: FROMGIT:, FROMLIST:,

  • If the patch has been merged into an upstream maintainer tree, but has not yet been merged into Linux mainline
    • tag the patch subject with FROMGIT:
    • add info on where the patch came from as (cherry picked from commit <sha1> <repo> <branch>). This must be a stable maintainer branch (not rebased, so don't use linux-next for example).
    • if changes were required, use BACKPORT: FROMGIT:
    • Example:
      • if the commit message in the maintainer tree is
        important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>
  • then Joe Smith would upload the patch for the common kernel as
        FROMGIT: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        (cherry picked from commit 878a2fd9de10b03d11d2f622250285c7e63deace
         https://git.kernel.org/pub/scm/linux/kernel/git/foo/bar.git test-branch)
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch has been submitted to LKML, but not accepted into any maintainer tree
    • tag the patch subject with FROMLIST:
    • add a Link: tag with a link to the submittal on lore.kernel.org
    • add a Bug: tag with the Android bug (required for patches not accepted into a maintainer tree)
    • if changes were required, use BACKPORT: FROMLIST:
    • Example:
        FROMLIST: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Link: https://lore.kernel.org/lkml/20190619171517.GA17557@someone.com/
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>

Requirements for Android-specific patches: ANDROID:

  • If the patch is fixing a bug to Android-specific code
    • tag the patch subject with ANDROID:
    • add a Fixes: tag that cites the patch with the bug
    • Example:
        ANDROID: fix android-specific bug in foobar.c

        This is the detailed description of the important fix

        Fixes: 1234abcd2468 ("foobar: add cool feature")
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch is a new feature
    • tag the patch subject with ANDROID:
    • add a Bug: tag with the Android bug (required for android-specific features)