On Mon, Jun 02, 2025 at 07:26:55PM +0000, Colton Lewis wrote:
> With FGT in place, the remaining trapped registers need to be written
> through to the underlying physical registers as well as the virtual
> ones. Failing to do this means delaying when guest writes take effect.
>
> Signed-off-by: Colton Lewis <[email protected]>
> ---
> arch/arm64/kvm/sys_regs.c | 27 +++++++++++++++++++++++++--
> 1 file changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index d368eeb4f88e..afd06400429a 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -18,6 +18,7 @@
> #include <linux/printk.h>
> #include <linux/uaccess.h>
> #include <linux/irqchip/arm-gic-v3.h>
> +#include <linux/perf/arm_pmu.h>
> #include <linux/perf/arm_pmuv3.h>
>
> #include <asm/arm_pmuv3.h>
> @@ -942,7 +943,11 @@ static bool pmu_counter_idx_valid(struct kvm_vcpu *vcpu,
> u64 idx)
> {
> u64 pmcr, val;
>
> - pmcr = kvm_vcpu_read_pmcr(vcpu);
> + if (kvm_vcpu_pmu_is_partitioned(vcpu))
> + pmcr = read_pmcr();
Reading PMCR_EL0 from EL2 is not going to have the desired effect.
PMCR_EL0.N only returns HPMN when read from the guest.
> + else
> + pmcr = kvm_vcpu_read_pmcr(vcpu);
> +
> val = FIELD_GET(ARMV8_PMU_PMCR_N, pmcr);
> if (idx >= val && idx != ARMV8_PMU_CYCLE_IDX) {
> kvm_inject_undefined(vcpu);
> @@ -1037,6 +1042,22 @@ static bool access_pmu_evcntr(struct kvm_vcpu *vcpu,
> return true;
> }
>
> +static void writethrough_pmevtyper(struct kvm_vcpu *vcpu, struct
> sys_reg_params *p,
> + u64 reg, u64 idx)
> +{
> + u64 evmask = kvm_pmu_evtyper_mask(vcpu->kvm);
> + u64 val = p->regval & evmask;
> +
> + __vcpu_sys_reg(vcpu, reg) = val;
> +
> + if (idx == ARMV8_PMU_CYCLE_IDX)
> + write_pmccfiltr(val);
> + else if (idx == ARMV8_PMU_INSTR_IDX)
> + write_pmicfiltr(val);
> + else
> + write_pmevtypern(idx, val);
> +}
> +
How are you preventing the VM from configuring an event counter to count
at EL2?
I see that you're setting MDCR_EL2.HPMD (which assumes FEAT_PMUv3p1) but
due to an architecture bug there's no control to prohibit the cycle
counter until FEAT_PMUv3p5 (MDCR_EL2.HCCD).
Since you're already trapping PMCCFILTR you could potentially configure
the hardware value in such a way that it filters EL2.
> static bool access_pmu_evtyper(struct kvm_vcpu *vcpu, struct sys_reg_params
> *p,
> const struct sys_reg_desc *r)
> {
> @@ -1063,7 +1084,9 @@ static bool access_pmu_evtyper(struct kvm_vcpu *vcpu,
> struct sys_reg_params *p,
> if (!pmu_counter_idx_valid(vcpu, idx))
> return false;
>
> - if (p->is_write) {
> + if (kvm_vcpu_pmu_is_partitioned(vcpu) && p->is_write) {
> + writethrough_pmevtyper(vcpu, p, reg, idx);
What about the vPMU event filter?
> + } else if (p->is_write) {
> kvm_pmu_set_counter_event_type(vcpu, p->regval, idx);
> kvm_vcpu_pmu_restore_guest(vcpu);
> } else {
> --
> 2.49.0.1204.g71687c7c1d-goog
>
Thanks,
Oliver
