[PATCH v1 0/4] KVM: arm64: Fix HCR_EL2 for non-protected VMs in pKVM

[Fuad Tabba <fuad.tabba@linux.dev>]

Hi folks,

In pKVM, EL2 sets a non-protected VM's HCR_EL2 in pkvm_vcpu_reset_hcr(),
which covers only part of vcpu_set_hcr(), and takes only TWI, TWE and
VSE from the host. As a result, an AArch32 VM can't run, a VM can read
GMID_EL1 or execute a TLBI OS its ID registers hide, and the host's TVM,
VI and VF never reach it.

Rather than add each missing bit at EL2, the third patch uses the host's
HCR_EL2 on every entry, except for the bits EL2 owns. A bit added to
vcpu_set_hcr() then reaches pKVM with no change at EL2, unless it opens
state EL2 doesn't switch, in which case it goes in PKVM_HCR_EL2_OWNED,
as ATA and DCT do.

The third patch depends on the first: once TTLBOS reaches the VM, a
trapped TLBI OS from a non-nested guest hits a WARN in
handle_tlbi_el1(), as it does without pKVM.

The last patch adds a selftest that checks a feature hidden in an ID
register is UNDEFINED in the guest. Its TLBI OS case fails in pKVM
before the third patch.

VSE still comes from the host as before. Syncing it back after delivery
is a separate fix [1].

Based on Linux 7.3-rc4 (93f51579e7df2).

Cheers,
/fuad

[1] https://lore.kernel.org/all/20260921101030.1231605-1-fuad.tabba@linux.dev/

Fuad Tabba (4):
  KVM: arm64: Don't WARN on an unsupported TLBI OS from vEL1
  KVM: arm64: Clear HCR_EL2.RW for 32-bit non-protected vCPUs
  KVM: arm64: Use the host's HCR_EL2 for non-protected VMs in pKVM
  KVM: arm64: selftests: Check a feature hidden in an ID register is
    UNDEF

 arch/arm64/include/asm/kvm_arm.h              |   1 +
 arch/arm64/kvm/hyp/include/nvhe/pkvm.h        |  13 ++
 arch/arm64/kvm/hyp/nvhe/hyp-main.c            |   7 +-
 arch/arm64/kvm/hyp/nvhe/pkvm.c                |  24 ++-
 arch/arm64/kvm/sys_regs.c                     |   7 +-
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../selftests/kvm/arm64/hidden_features.c     | 184 ++++++++++++++++++
 7 files changed, 222 insertions(+), 15 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/arm64/hidden_features.c


base-commit: 93f51579e7df248780214094418f205253383cc5
-- 
2.39.5