Re: [PATCH v4 08/14] RISC-V: KVM: Add SBI PMU extension support
From: Atish Patra
Date: Fri Feb 03 2023 - 04:08:18 EST
On Thu, Feb 2, 2023 at 9:29 AM Andrew Jones <ajones@xxxxxxxxxxxxxxxx> wrote:
>
> On Wed, Feb 01, 2023 at 03:12:44PM -0800, Atish Patra wrote:
> > SBI PMU extension allows KVM guests to configure/start/stop/query about
> > the PMU counters in virtualized enviornment as well.
> >
> > In order to allow that, KVM implements the entire SBI PMU extension.
> >
> > Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>
> > Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx>
> > ---
> > arch/riscv/kvm/Makefile | 2 +-
> > arch/riscv/kvm/vcpu_sbi.c | 11 +++++
> > arch/riscv/kvm/vcpu_sbi_pmu.c | 85 +++++++++++++++++++++++++++++++++++
> > 3 files changed, 97 insertions(+), 1 deletion(-)
> > create mode 100644 arch/riscv/kvm/vcpu_sbi_pmu.c
> >
> > diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
> > index 5de1053..278e97c 100644
> > --- a/arch/riscv/kvm/Makefile
> > +++ b/arch/riscv/kvm/Makefile
> > @@ -25,4 +25,4 @@ kvm-y += vcpu_sbi_base.o
> > kvm-y += vcpu_sbi_replace.o
> > kvm-y += vcpu_sbi_hsm.o
> > kvm-y += vcpu_timer.o
> > -kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_pmu.o
> > +kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_pmu.o vcpu_sbi_pmu.o
> > diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
> > index fe2897e..15fde15 100644
> > --- a/arch/riscv/kvm/vcpu_sbi.c
> > +++ b/arch/riscv/kvm/vcpu_sbi.c
> > @@ -20,6 +20,16 @@ static const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_v01 = {
> > };
> > #endif
> >
> > +#ifdef CONFIG_RISCV_PMU_SBI
> > +extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pmu;
> > +#else
> > +static const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pmu = {
> > + .extid_start = -1UL,
> > + .extid_end = -1UL,
> > + .handler = NULL,
> > +};
> > +#endif
> > +
> > static const struct kvm_vcpu_sbi_extension *sbi_ext[] = {
> > &vcpu_sbi_ext_v01,
> > &vcpu_sbi_ext_base,
> > @@ -28,6 +38,7 @@ static const struct kvm_vcpu_sbi_extension *sbi_ext[] = {
> > &vcpu_sbi_ext_rfence,
> > &vcpu_sbi_ext_srst,
> > &vcpu_sbi_ext_hsm,
> > + &vcpu_sbi_ext_pmu,
> > &vcpu_sbi_ext_experimental,
> > &vcpu_sbi_ext_vendor,
> > };
> > diff --git a/arch/riscv/kvm/vcpu_sbi_pmu.c b/arch/riscv/kvm/vcpu_sbi_pmu.c
> > new file mode 100644
> > index 0000000..e028b0a
> > --- /dev/null
> > +++ b/arch/riscv/kvm/vcpu_sbi_pmu.c
> > @@ -0,0 +1,85 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (c) 2023 Rivos Inc
> > + *
> > + * Authors:
> > + * Atish Patra <atishp@xxxxxxxxxxxx>
> > + */
> > +
> > +#include <linux/errno.h>
> > +#include <linux/err.h>
> > +#include <linux/kvm_host.h>
> > +#include <asm/csr.h>
> > +#include <asm/sbi.h>
> > +#include <asm/kvm_vcpu_sbi.h>
> > +
> > +static int kvm_sbi_ext_pmu_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
> > + struct kvm_vcpu_sbi_return *retdata)
> > +{
> > + int ret = 0;
> > + struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
> > + struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> > + unsigned long funcid = cp->a6;
> > + uint64_t temp;
> > +
> > + /* Return not supported if PMU is not initialized */
> > + if (!kvpmu->init_done)
> > + return -EINVAL;
>
> Shouldn't this be the following?
>
> if (!kvpmu->init_done)
> retdata->err_val = SBI_ERR_NOT_SUPPORTED;
> return 0;
> }
>
This condition presents an additional sanity check and indicates a bug
in the guest code
where it invokes PMU extension calls when the probe function already
returns NOT_SUPPORTED.
Earlier, I was in two minds whether this should just return not
supported to the guest or report an
error. However, given that it's just a driver in the guest, the error
shouldn't be fatal. It should just
return the sbi error back to the guest.
Thanks for catching this. I have fixed it in v5.
> > +
> > + switch (funcid) {
> > + case SBI_EXT_PMU_NUM_COUNTERS:
> > + ret = kvm_riscv_vcpu_pmu_num_ctrs(vcpu, retdata);
> > + break;
> > + case SBI_EXT_PMU_COUNTER_GET_INFO:
> > + ret = kvm_riscv_vcpu_pmu_ctr_info(vcpu, cp->a0, retdata);
> > + break;
> > + case SBI_EXT_PMU_COUNTER_CFG_MATCH:
> > +#if defined(CONFIG_32BIT)
> > + temp = ((uint64_t)cp->a5 << 32) | cp->a4;
> > +#else
> > + temp = cp->a4;
> > +#endif
> > + /*
> > + * This can fail if perf core framework fails to create an event.
> > + * Forward the error to the user space because its an error happened
>
> "Forward the error to userspace because it's an error which happened within
> the host kernel."
>
Fixed.
> > + * within host kernel. The other option would be convert this to
> ^ to
> > + * an SBI error and forward to the guest.
> > + */
> > + ret = kvm_riscv_vcpu_pmu_ctr_cfg_match(vcpu, cp->a0, cp->a1,
> > + cp->a2, cp->a3, temp, retdata);
> > + break;
> > + case SBI_EXT_PMU_COUNTER_START:
> > +#if defined(CONFIG_32BIT)
> > + temp = ((uint64_t)cp->a4 << 32) | cp->a3;
> > +#else
> > + temp = cp->a3;
> > +#endif
> > + ret = kvm_riscv_vcpu_pmu_ctr_start(vcpu, cp->a0, cp->a1, cp->a2,
> > + temp, retdata);
> > + break;
> > + case SBI_EXT_PMU_COUNTER_STOP:
> > + ret = kvm_riscv_vcpu_pmu_ctr_stop(vcpu, cp->a0, cp->a1, cp->a2, retdata);
> > + break;
> > + case SBI_EXT_PMU_COUNTER_FW_READ:
> > + ret = kvm_riscv_vcpu_pmu_ctr_read(vcpu, cp->a0, retdata);
> > + break;
> > + default:
> > + retdata->err_val = SBI_ERR_NOT_SUPPORTED;
> > + }
> > +
> > + return ret;
> > +}
> > +
> > +unsigned long kvm_sbi_ext_pmu_probe(struct kvm_vcpu *vcpu)
> > +{
> > + struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> > +
> > + return kvpmu->init_done;
> > +}
> > +
> > +const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pmu = {
> > + .extid_start = SBI_EXT_PMU,
> > + .extid_end = SBI_EXT_PMU,
> > + .handler = kvm_sbi_ext_pmu_handler,
> > + .probe = kvm_sbi_ext_pmu_probe,
> > +};
> > --
> > 2.25.1
> >
>
> Thanks,
> drew
--
Regards,
Atish