[RFC PATCH 0/5] KVM: arm64: New PTE dirty-page encoding, HAFDBS new usage

[Leonardo Bras]

This series have 2 main goals:

1 - Patches #1,#2,#3 : Change the PTE descriptor to use WD/WC/RO encodings
    making use of the DBM bit, adapting all usages, and
2 - Patches #4,#5 are an RFC on using HAFDBS on a guest to avoid resetting
    all PTEs to WC when dirty-logging starts, speeding-up startup.

(1) will also introduce a new walker for cleaning the dirty-bit, which will
clear the DBM bit if it's a block mapping (hugepage). This is needed as on
lazy-splitting we need to fault a write so we can do the lazy splitting.
This is needed for both the next patches, and for HDBSS & HACDBS
enablement.

On (2), I really just want feedback to understand if it's worth pursuing.
My main idea is that we can use HAFDBS _outside_ dirty-logging to only mark
dirty the pages that were actually written to. That is supposed to make it
faster to transverse the pagetables when we need to clean the dirty-bit, as
there is potentially less atomic writes to perform. The price paid for that
is disabling HAFDBS on every vcpu before we can start cleaning the pages,
done by a (new) vcpu request.

Please let me know of what do you think!

Thanks!
Leo

Leonardo Bras (5):
  KVM: arm64: pgtables: Change write bit from S2AP_W to DBM
  KVM: arm64: Add KVM_PGTABLE_PROT_DIRTY
  KVM: arm64: Introduce a dedicated walker for stage2 write-protect
  KVM: arm64: Add KVM_REQ_RELOAD_STAGE2
  KVM: arm64: Enable HAFDBS for guests not on migration

 arch/arm64/include/asm/kvm_host.h    |  2 ++
 arch/arm64/include/asm/kvm_mmu.h     |  6 ++++
 arch/arm64/include/asm/kvm_nested.h  |  9 +++--
 arch/arm64/include/asm/kvm_pgtable.h | 12 +++++--
 arch/arm64/kvm/arm.c                 | 15 ++++++++
 arch/arm64/kvm/hyp/pgtable.c         | 49 +++++++++++++++++++++-----
 arch/arm64/kvm/mmu.c                 | 51 ++++++++++++++++++++++------
 arch/arm64/kvm/nested.c              |  4 ++-
 arch/arm64/kvm/ptdump.c              | 10 ++++--
 9 files changed, 130 insertions(+), 28 deletions(-)


base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
-- 
2.55.0