On Fri, Aug 05, 2022 at 02:58:04PM +0100, Marc Zyngier wrote: > Ricardo recently reported[1] that our PMU emulation was busted when it > comes to chained events, as we cannot expose the overflow on a 32bit > boundary (which the architecture requires). > > This series aims at fixing this (by deleting a lot of code), and as a > bonus adds support for PMUv3p5, as this requires us to fix a few more > things. > > Tested on A53 (PMUv3) and FVP (PMUv3p5). > > [1] https://lore.kernel.org/r/20220805004139.990531-1-ricarkol@xxxxxxxxxx > > Marc Zyngier (9): > KVM: arm64: PMU: Align chained counter implementation with > architecture pseudocode > KVM: arm64: PMU: Distinguish between 64bit counter and 64bit overflow > KVM: arm64: PMU: Only narrow counters that are not 64bit wide > KVM: arm64: PMU: Add counter_index_to_*reg() helpers > KVM: arm64: PMU: Simplify setting a counter to a specific value > KVM: arm64: PMU: Move the ID_AA64DFR0_EL1.PMUver limit to VM creation > KVM: arm64: PMU: Aleven ID_AA64DFR0_EL1.PMUver to be set from userspace > KVM: arm64: PMU: Implement PMUv3p5 long counter support > KVM: arm64: PMU: Aleven PMUv3p5 to be exposed to the guest > > arch/arm64/include/asm/kvm_host.h | 1 + > arch/arm64/kvm/arm.c | 6 + > arch/arm64/kvm/pmu-emul.c | 372 ++++++++++-------------------- > arch/arm64/kvm/sys_regs.c | 65 +++++- > include/kvm/arm_pmu.h | 16 +- > 5 files changed, 208 insertions(+), 252 deletions(-) > > -- > 2.34.1 > Hi Marc, There is one extra potential issue with exposing PMUv3p5. I see this weird behavior when doing passthrough ("bare metal") on the fast-model configured to emulate PMUv3p5: the [63:32] half of the counters overflowing at 32-bits is still incremented. Fast model - ARMv8.5: Assuming the initial state is even=0xFFFFFFFF and odd=0x0, incrementing the even counter leads to: 0x00000001_00000000 0x00000000_00000001 0x1 even counter odd counter PMOVSET Assuming the initial state is even=0xFFFFFFFF and odd=0xFFFFFFFF, incrementing the even counter leads to: 0x00000001_00000000 0x00000001_00000000 0x3 even counter odd counter PMOVSET More specifically, the pmu-chained-sw-incr kvm-unit-test fails when doing passthrough of PMUv3p5 (fast model - ARMv8.5): INFO: PMU version: 0x5 INFO: PMU implementer/ID code: 0x41("A")/0 INFO: Implements 8 event counters PASS: pmu: pmu-chained-sw-incr: overflow and chain counter incremented after 100 SW_INCR/CHAIN INFO: pmu: pmu-chained-sw-incr: overflow=0x1, #0=4294967380 #1=1 ^^^^^^^^^^^^^ #0=0x00000001_00000054 #1=0x00000000_00000001 FAIL: pmu: pmu-chained-sw-incr: expected overflows and values after 100 SW_INCR/CHAIN INFO: pmu: pmu-chained-sw-incr: overflow=0x3, #0=4294967380 #1=4294967296 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ #0=0x00000001_00000054 #1=0x00000001_00000000 There's really no good use for this behavior, and not sure if it's worth emulating it. Can't find any reference in the ARM ARM. Thanks, Ricardo
