[PATCH v6 0/7] KVM: arm64: Hide unsupported MPAM from the guest
Marc Zyngier
maz at kernel.org
Thu Oct 31 06:11:56 PDT 2024
On Wed, 30 Oct 2024 16:03:10 +0000,
Joey Gouly <joey.gouly at arm.com> wrote:
>
> Hi,
>
> changes since v5 [1]:
> - Removed Kconfig option, the KVM traps shouldn't rely on host kernel support
> - Renamed cpus_support_* to system_supports_* since that matches other functions
> - Replace static branch arm64_mpam_has_hcr with a normal cpufeature capability
> - Add MPAM*_EL2 regs to KVM (undef_access)
> - Use constants in the test, instead of hardcoded values
> - Added R-b and T-b tags
> - Rebased on v6.12-rc5
>
> James wrote:
> This series fixes up a long standing bug where MPAM was accidentally exposed
> to a guest, but the feature was not otherwise trapped or context switched.
> This could result in KVM warning about unexpected traps, and injecting an
> undef into the guest contradicting the ID registers.
> This would prevent an MPAM aware kernel from booting - fortunately, there
> aren't any of those.
>
> Ideally, we'd take the MPAM feature away from the ID registers, but that
> would leave existing guests unable to migrate to a newer kernel. Instead,
> just ignore that field when it matches the hardware. KVM wasn't going to
> expose MPAM anyway. The guest will not see MPAM in the id registers.
>
> This series includes the head.S and KVM changes to enable/disable traps. If
> MPAM is neither enabled nor emulated by EL3 firmware, these system register
> accesses will trap to EL3.
> If your kernel doesn't boot, and the problem bisects here - please update
> your firmware. MPAM has been supported by trusted firmware since v1.6 in
> 2018. (also noted on patch 3).
>
> Thanks,
> Joey
>
> [1] https://lore.kernel.org/kvmarm/20241015133923.3910916-1-joey.gouly@arm.com/
>
> James Morse (7):
> arm64/sysreg: Convert existing MPAM sysregs and add the remaining
> entries
> arm64: head.S: Initialise MPAM EL2 registers and disable traps
> arm64: cpufeature: discover CPU support for MPAM
> KVM: arm64: Fix missing traps of guest accesses to the MPAM registers
> KVM: arm64: Add a macro for creating filtered sys_reg_descs entries
> KVM: arm64: Disable MPAM visibility by default and ignore VMM writes
> KVM: arm64: selftests: Test ID_AA64PFR0.MPAM isn't completely ignored
>
> .../arch/arm64/cpu-feature-registers.rst | 2 +
> arch/arm64/include/asm/cpu.h | 1 +
> arch/arm64/include/asm/cpucaps.h | 5 +
> arch/arm64/include/asm/cpufeature.h | 17 ++
> arch/arm64/include/asm/el2_setup.h | 14 ++
> arch/arm64/include/asm/kvm_arm.h | 1 +
> arch/arm64/include/asm/sysreg.h | 12 --
> arch/arm64/kernel/cpufeature.c | 96 +++++++++++
> arch/arm64/kernel/cpuinfo.c | 3 +
> arch/arm64/kvm/hyp/include/hyp/switch.h | 31 ++++
> arch/arm64/kvm/sys_regs.c | 121 +++++++++----
> arch/arm64/tools/cpucaps | 2 +
> arch/arm64/tools/sysreg | 161 ++++++++++++++++++
> .../selftests/kvm/aarch64/set_id_regs.c | 99 ++++++++++-
> 14 files changed, 523 insertions(+), 42 deletions(-)
For the series:
Reviewed-by: Marc Zyngier <maz at kernel.org>
M.
--
Without deviation from the norm, progress is not possible.
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