Hi Drew,

I see this series takes the approach we currently have in KVM of masking
features we don't want to expose to the guest. This approach adds yet
another "reject list" to be maintained as hardware evolves. I'd rather see
that we first change KVM to using an accept list, i.e. mask everything and
then only set what we want to enable. Mimicking that new accept list in
pKVM, where much less would be enabled, would reduce the amount of
maintenance needed.

Good point. I agree that having an allow list is preferable to having
a block list. The way this patch series handles system register
accesses is actually an allow list. However, as it is now, features
being exposed to protected guests via the feature registers take the
block list approach. I will fix that to ensure that instead it exposes
a list of allowed features, rather than hiding restricted ones. As you
suggest, this would reduce the amount of maintenance as hardware
evolves and is better for security as well.

As for changing KVM first, I think that that's orthogonal to what this
series is trying to accomplish. Features in pKVM are not controlled or
negotiable by userspace, as it is a fixed virtual platform. When KVM
changes to use allow lists instead, it shouldn't conflict with how
this series works, especially if I fix it to use an allow list
instead.

Thanks for your feedback.

Cheers,
/fuad

Thanks,
drew

quoted

This series is based on kvmarm/next and Will's patches for an Initial pKVM user
ABI [1]. You can find the applied series here [2].

Cheers,
/fuad

[1] https://lore.kernel.org/kvmarm/20210603183347.1695-1-will@kernel.org/ (local)

For more details about pKVM, please refer to Will's talk at KVM Forum 2020:
https://www.youtube.com/watch?v=edqJSzsDRxk

[2] https://android-kvm.googlesource.com/linux/+/refs/heads/tabba/el2_fixed_feature_v1

To: kvmarm@lists.cs.columbia.edu
Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Alexandru Elisei <redacted>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Christoffer Dall <redacted>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Quentin Perret <redacted>
Cc: kvm@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: kernel-team@android.com

Fuad Tabba (13):
  KVM: arm64: Remove trailing whitespace in comments
  KVM: arm64: MDCR_EL2 is a 64-bit register
  KVM: arm64: Fix name of HCR_TACR to match the spec
  KVM: arm64: Refactor sys_regs.h,c for nVHE reuse
  KVM: arm64: Restore mdcr_el2 from vcpu
  KVM: arm64: Add feature register flag definitions
  KVM: arm64: Add config register bit definitions
  KVM: arm64: Guest exit handlers for nVHE hyp
  KVM: arm64: Add trap handlers for protected VMs
  KVM: arm64: Move sanitized copies of CPU features
  KVM: arm64: Trap access to pVM restricted features
  KVM: arm64: Handle protected guests at 32 bits
  KVM: arm64: Check vcpu features at pVM creation

 arch/arm64/include/asm/kvm_arm.h        |  34 +-
 arch/arm64/include/asm/kvm_asm.h        |   2 +-
 arch/arm64/include/asm/kvm_host.h       |   2 +-
 arch/arm64/include/asm/kvm_hyp.h        |   4 +
 arch/arm64/include/asm/sysreg.h         |   6 +
 arch/arm64/kvm/arm.c                    |   4 +
 arch/arm64/kvm/debug.c                  |   5 +-
 arch/arm64/kvm/hyp/include/hyp/switch.h |  42 ++
 arch/arm64/kvm/hyp/nvhe/Makefile        |   2 +-
 arch/arm64/kvm/hyp/nvhe/debug-sr.c      |   2 +-
 arch/arm64/kvm/hyp/nvhe/mem_protect.c   |   6 -
 arch/arm64/kvm/hyp/nvhe/switch.c        | 114 +++++-
 arch/arm64/kvm/hyp/nvhe/sys_regs.c      | 501 ++++++++++++++++++++++++
 arch/arm64/kvm/hyp/vhe/debug-sr.c       |   2 +-
 arch/arm64/kvm/pkvm.c                   |  31 ++
 arch/arm64/kvm/sys_regs.c               |  62 +--
 arch/arm64/kvm/sys_regs.h               |  35 ++
 17 files changed, 782 insertions(+), 72 deletions(-)
 create mode 100644 arch/arm64/kvm/hyp/nvhe/sys_regs.c


base-commit: 35b256a5eebe3ac715b4ea6234aa4236a10d1a88
--
2.32.0.rc1.229.g3e70b5a671-goog

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