| Message ID | 20250409160106.6445-1-maz@kernel.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: arm64: EL2 PMU handling fixes | expand |
On Wed, Apr 09, 2025 at 05:01:00PM +0100, Marc Zyngier wrote: > Joey reports that some of his PMU tests do not behave quite as > expected: > > - MDCR_EL2.HPMN is set to 0 out of reset > > - PMCR_EL0.P should reset all the counters when written from EL2 > > Oliver points out that setting PMCR_EL0.N from userspace by writing to > the register is silly with NV, and that we need a new PMU attribute > instead. > > On top of that, I figured out that we had a number of little gotchas: > > - It is possible for a guest to write an HPMN value that is out of > bound, and it seems valuable to limit it > > - PMCR_EL0.N should be the maximum number of counters when read from > EL2, and MDCR_EL2.HPMN when read from EL0/EL1 > > - Prevent userspace from updating PMCR_EL0.N when EL2 is available > > I haven't added any Cc stable, as NV is not functional upstream yet. Similarly, I don't see a compelling reason for this to go in as a fix for 6.15, especially since you're adding new UAPI. Do you mind grabbing it for the next merge window? With the comments addressed: Reviewed-by: Oliver Upton <oliver.upton@linux.dev> Thanks, Oliver
On Wed, 09 Apr 2025 21:31:31 +0100, Oliver Upton <oliver.upton@linux.dev> wrote: > > On Wed, Apr 09, 2025 at 05:01:00PM +0100, Marc Zyngier wrote: > > Joey reports that some of his PMU tests do not behave quite as > > expected: > > > > - MDCR_EL2.HPMN is set to 0 out of reset > > > > - PMCR_EL0.P should reset all the counters when written from EL2 > > > > Oliver points out that setting PMCR_EL0.N from userspace by writing to > > the register is silly with NV, and that we need a new PMU attribute > > instead. > > > > On top of that, I figured out that we had a number of little gotchas: > > > > - It is possible for a guest to write an HPMN value that is out of > > bound, and it seems valuable to limit it > > > > - PMCR_EL0.N should be the maximum number of counters when read from > > EL2, and MDCR_EL2.HPMN when read from EL0/EL1 > > > > - Prevent userspace from updating PMCR_EL0.N when EL2 is available > > > > I haven't added any Cc stable, as NV is not functional upstream yet. > > Similarly, I don't see a compelling reason for this to go in as a fix > for 6.15, especially since you're adding new UAPI. Do you mind grabbing > it for the next merge window? > > With the comments addressed: > > Reviewed-by: Oliver Upton <oliver.upton@linux.dev> Thanks. I'll repost the whole thing next week and queue it for 6.16. M.
Joey reports that some of his PMU tests do not behave quite as expected: - MDCR_EL2.HPMN is set to 0 out of reset - PMCR_EL0.P should reset all the counters when written from EL2 Oliver points out that setting PMCR_EL0.N from userspace by writing to the register is silly with NV, and that we need a new PMU attribute instead. On top of that, I figured out that we had a number of little gotchas: - It is possible for a guest to write an HPMN value that is out of bound, and it seems valuable to limit it - PMCR_EL0.N should be the maximum number of counters when read from EL2, and MDCR_EL2.HPMN when read from EL0/EL1 - Prevent userspace from updating PMCR_EL0.N when EL2 is available I haven't added any Cc stable, as NV is not functional upstream yet. * From v1 [1]: - Added patch for the new PMU attribute - Added fix for HPMN limit - Prevent update of PMCR_EL0.N with NV - Fix kvm_vcpu_read_pmcr() - Rebased on 6.15-rc1 [1] https://lore.kernel.org/r/20250217112412.3963324-1-maz@kernel.org Marc Zyngier (6): KVM: arm64: Fix MDCR_EL2.HPMN reset value KVM: arm64: Contextualise the handling of PMCR_EL0.P writes KVM: arm64: Allow userspace to limit the number of PMU counters for EL2 VMs KVM: arm64: Don't let userspace write to PMCR_EL0.N when the vcpu has EL2 KVM: arm64: Handle out-of-bound write to HDCR_EL2.HPMN KVM: arm64: Let kvm_vcpu_read_pmcr() return an EL-dependent value for PMCR_EL0.N Documentation/virt/kvm/devices/vcpu.rst | 24 ++++++++++++ arch/arm64/include/uapi/asm/kvm.h | 9 +++-- arch/arm64/kvm/pmu-emul.c | 51 ++++++++++++++++++++++--- arch/arm64/kvm/sys_regs.c | 43 ++++++++++++++++----- 4 files changed, 107 insertions(+), 20 deletions(-)