[RFC,0/3] Fix several bugs in KVM stage 2 translation

Message

Yanan Wang Nov. 30, 2020, 12:18 p.m. UTC

Several problems about KVM stage 2 translation were found when testing based
on the mainline code. The following is description of the problems and the
corresponding patchs.

When installing a new pte entry or updating an old valid entry in stage 2
translation, we use get_page()/put_page() to record page_count of the page-table
pages. PATCH 1/3 aims to fix incorrect use of get_page()/put_page() in stage 2,
which might make page-table pages unable to be freed when unmapping a range.

When dirty logging of a guest with hugepages is finished, we should merge tables
back into a block entry if adjustment of huge mapping is found necessary.
In addition to installing the block entry, mapping of the lower-levels for the
block should also be unmapped to avoid multiple TLB entries.
PATCH 2/3 adds unmap operation when merge tables into a block entry.

The rewrite of page-table code and fault handling add two different handlers
for "just relaxing permissions" and "map by stage2 page-table walk", that's
great improvement. Yet, in function user_mem_abort(), conditions where we choose
the above two fault handlers are not strictly distinguished. This will causes
guest errors such as infinite-loop (soft lockup will occur in result), because of
calling the inappropriate fault handler. So, a solution that can strictly
distinguish conditions is introduced in PATCH 3/3.

Yanan Wang (3):
  KVM: arm64: Fix possible memory leak in kvm stage2
  KVM: arm64: Fix handling of merging tables into a block entry
  KVM: arm64: Add usage of stage 2 fault lookup level in
    user_mem_abort()

 arch/arm64/include/asm/esr.h         |  1 +
 arch/arm64/include/asm/kvm_emulate.h |  5 +++++
 arch/arm64/kvm/hyp/pgtable.c         | 22 +++++++++++++++++-----
 arch/arm64/kvm/mmu.c                 | 11 +++++++++--
 4 files changed, 32 insertions(+), 7 deletions(-)