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[0/1] KVM: arm64: Skip RCU protection for hyp stage-1

Message ID 20221114201127.1814794-1-oliver.upton@linux.dev (mailing list archive)
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Series KVM: arm64: Skip RCU protection for hyp stage-1 | expand

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Oliver Upton Nov. 14, 2022, 8:11 p.m. UTC 
Whelp, that was quick.

Marek reports [1] that the parallel faults series leads to a kernel BUG
when initializing the hyp stage-1 page tables. Work around the issue by
never acquiring the RCU read lock when walking hyp stage-1. This is safe
because hyp stage-1 is protected by a spinlock (pKVM) or mutex (regular
nVHE).

The included patch applies to the parallel faults series. To avoid
breaking bisection, the patch should immediately precede commit
c3119ae45dfb ("KVM: arm64: Protect stage-2 traversal with RCU"). Or, if
preferred, I can respin the whole series in the correct order.

Tested with the pKVM isolated vCPU state series [2] merged on top, w/
kvm-arm.mode={nvhe,protected} on an Ampere Altra system.

Cc: Marek Szyprowski <m.szyprowski@samsung.com>

[1]: https://lore.kernel.org/kvmarm/d9854277-0411-8169-9e8b-68d15e4c0248@samsung.com/
[2]: https://lore.kernel.org/linux-arm-kernel/20221110190259.26861-1-will@kernel.org/

Oliver Upton (1):
  KVM: arm64: Use a separate function for hyp stage-1 walks

 arch/arm64/include/asm/kvm_pgtable.h | 24 ++++++++++++++++++++++++
 arch/arm64/kvm/hyp/nvhe/setup.c      |  2 +-
 arch/arm64/kvm/hyp/pgtable.c         | 18 +++++++++++++++---
 3 files changed, 40 insertions(+), 4 deletions(-)