Re: [PATCH v6 05/10] KVM: arm64: Support stolen time reporting via shared structure

Marc Zyngier
2019-10-19T11:12:34Z

On Fri, 11 Oct 2019 13:59:25 +0100,
Steven Price <steven.price@arm.com> wrote:
>
> Implement the service call for configuring a shared structure between a
> VCPU and the hypervisor in which the hypervisor can write the time
> stolen from the VCPU's execution time by other tasks on the host.
>
> User space allocates memory which is placed at an IPA also chosen by user
> space. The hypervisor then updates the shared structure using
> kvm_put_guest() to ensure single copy atomicity of the 64-bit value
> reporting the stolen time in nanoseconds.
>
> Whenever stolen time is enabled by the guest, the stolen time counter is
> reset.
>
> The stolen time itself is retrieved from the sched_info structure
> maintained by the Linux scheduler code. We enable SCHEDSTATS when
> selecting KVM Kconfig to ensure this value is meaningful.
>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> arch/arm/include/asm/kvm_host.h | 20 +++++++++++
> arch/arm64/include/asm/kvm_host.h | 21 +++++++++++-
> arch/arm64/kvm/Kconfig | 1 +
> include/linux/kvm_types.h | 2 ++
> virt/kvm/arm/arm.c | 11 ++++++
> virt/kvm/arm/hypercalls.c | 3 ++
> virt/kvm/arm/pvtime.c | 56 +++++++++++++++++++++++++++++++
> 7 files changed, 113 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 5a0c3569ebde..5c401482d62d 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -39,6 +39,7 @@
> KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> #define KVM_REQ_IRQ_PENDING KVM_ARCH_REQ(1)
> #define KVM_REQ_VCPU_RESET KVM_ARCH_REQ(2)
> +#define KVM_REQ_RECORD_STEAL KVM_ARCH_REQ(3)
>
> DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
>
> @@ -329,6 +330,25 @@ static inline long kvm_hypercall_pv_features(struct kvm_vcpu *vcpu)
> return SMCCC_RET_NOT_SUPPORTED;
> }
>
> +static inline long kvm_hypercall_stolen_time(struct kvm_vcpu *vcpu)
> +{
> + return SMCCC_RET_NOT_SUPPORTED;
> +}
> +
> +static inline int kvm_update_stolen_time(struct kvm_vcpu *vcpu, bool init)
> +{
> + return -ENOTSUPP;
> +}
> +
> +static inline void kvm_arm_pvtime_vcpu_init(struct kvm_vcpu_arch *vcpu_arch)
> +{
> +}
> +
> +static inline bool kvm_arm_is_pvtime_enabled(struct kvm_vcpu_arch *vcpu_arch)
> +{
> + return false;
> +}
> +
> void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>
> struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 93b46d9526d0..1697e63f6dd8 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -44,6 +44,7 @@
> KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> #define KVM_REQ_IRQ_PENDING KVM_ARCH_REQ(1)
> #define KVM_REQ_VCPU_RESET KVM_ARCH_REQ(2)
> +#define KVM_REQ_RECORD_STEAL KVM_ARCH_REQ(3)
>
> DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
>
> @@ -338,8 +339,14 @@ struct kvm_vcpu_arch {
> /* True when deferrable sysregs are loaded on the physical CPU,
> * see kvm_vcpu_load_sysregs and kvm_vcpu_put_sysregs. */
> bool sysregs_loaded_on_cpu;
> -};
>
> + /* Guest PV state */
> + struct {
> + u64 steal;
> + u64 last_steal;
> + gpa_t base;
> + } steal;
> +};

nit: Please keep an empty line at the end of the structure.

> /* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */
> #define vcpu_sve_pffr(vcpu) ((void *)((char *)((vcpu)->arch.sve_state) + \
> sve_ffr_offset((vcpu)->arch.sve_max_vl)))
> @@ -479,6 +486,18 @@ int kvm_perf_init(void);
> int kvm_perf_teardown(void);
>
> long kvm_hypercall_pv_features(struct kvm_vcpu *vcpu);
> +long kvm_hypercall_stolen_time(struct kvm_vcpu *vcpu);
> +int kvm_update_stolen_time(struct kvm_vcpu *vcpu, bool init);
> +
> +static inline void kvm_arm_pvtime_vcpu_init(struct kvm_vcpu_arch *vcpu_arch)
> +{
> + vcpu_arch->steal.base = GPA_INVALID;
> +}
> +
> +static inline bool kvm_arm_is_pvtime_enabled(struct kvm_vcpu_arch *vcpu_arch)
> +{
> + return (vcpu_arch->steal.base != GPA_INVALID);
> +}
>
> void kvm_set_sei_esr(struct kvm_vcpu *vcpu, u64 syndrome);
>
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index a67121d419a2..d8b88e40d223 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -39,6 +39,7 @@ config KVM
> select IRQ_BYPASS_MANAGER
> select HAVE_KVM_IRQ_BYPASS
> select HAVE_KVM_VCPU_RUN_PID_CHANGE
> + select SCHEDSTATS
> ---help---
> Support hosting virtualized guest machines.
> We don't support KVM with 16K page tables yet, due to the multiple
> diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
> index bde5374ae021..1c88e69db3d9 100644
> --- a/include/linux/kvm_types.h
> +++ b/include/linux/kvm_types.h
> @@ -35,6 +35,8 @@ typedef unsigned long gva_t;
> typedef u64 gpa_t;
> typedef u64 gfn_t;
>
> +#define GPA_INVALID (~(gpa_t)0)
> +
> typedef unsigned long hva_t;
> typedef u64 hpa_t;
> typedef u64 hfn_t;
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 86c6aa1cb58e..5d3059aeadb1 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -40,6 +40,10 @@
> #include <asm/kvm_coproc.h>
> #include <asm/sections.h>
>
> +#include <kvm/arm_hypercalls.h>
> +#include <kvm/arm_pmu.h>
> +#include <kvm/arm_psci.h>
> +
> #ifdef REQUIRES_VIRT
> __asm__(".arch_extension virt");
> #endif
> @@ -351,6 +355,8 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
>
> kvm_arm_reset_debug_ptr(vcpu);
>
> + kvm_arm_pvtime_vcpu_init(&vcpu->arch);
> +
> return kvm_vgic_vcpu_init(vcpu);
> }
>
> @@ -380,6 +386,8 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> kvm_vcpu_load_sysregs(vcpu);
> kvm_arch_vcpu_load_fp(vcpu);
> kvm_vcpu_pmu_restore_guest(vcpu);
> + if (kvm_arm_is_pvtime_enabled(&vcpu->arch))
> + kvm_make_request(KVM_REQ_RECORD_STEAL, vcpu);
>
> if (single_task_running())
> vcpu_clear_wfe_traps(vcpu);
> @@ -645,6 +653,9 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu)
> * that a VCPU sees new virtual interrupts.
> */
> kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu);
> +
> + if (kvm_check_request(KVM_REQ_RECORD_STEAL, vcpu))
> + kvm_update_stolen_time(vcpu, false);
> }
> }
>
> diff --git a/virt/kvm/arm/hypercalls.c b/virt/kvm/arm/hypercalls.c
> index 97ea8b133e77..5c333a64390e 100644
> --- a/virt/kvm/arm/hypercalls.c
> +++ b/virt/kvm/arm/hypercalls.c
> @@ -56,6 +56,9 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> case ARM_SMCCC_HV_PV_TIME_FEATURES:
> val = kvm_hypercall_pv_features(vcpu);
> break;
> + case ARM_SMCCC_HV_PV_TIME_ST:
> + val = kvm_hypercall_stolen_time(vcpu);
> + break;
> default:
> return kvm_psci_call(vcpu);
> }
> diff --git a/virt/kvm/arm/pvtime.c b/virt/kvm/arm/pvtime.c
> index 8d0fad671dcf..a90f1b4ebd13 100644
> --- a/virt/kvm/arm/pvtime.c
> +++ b/virt/kvm/arm/pvtime.c
> @@ -3,8 +3,45 @@
>
> #include <linux/arm-smccc.h>
>
> +#include <asm/pvclock-abi.h>
> +
> #include <kvm/arm_hypercalls.h>
>
> +int kvm_update_stolen_time(struct kvm_vcpu *vcpu, bool init)
> +{
> + struct kvm *kvm = vcpu->kvm;
> + u64 steal;
> + u64 steal_le;

This should be __le64.

> + u64 offset;
> + int idx;
> + u64 base = vcpu->arch.steal.base;
> +
> + if (base == GPA_INVALID)
> + return -ENOTSUPP;
> +
> + /* Let's do the local bookkeeping */
> + steal = vcpu->arch.steal.steal;
> + steal += current->sched_info.run_delay - vcpu->arch.steal.last_steal;
> + vcpu->arch.steal.last_steal = current->sched_info.run_delay;
> + vcpu->arch.steal.steal = steal;
> +
> + steal_le = cpu_to_le64(steal);
> + idx = srcu_read_lock(&kvm->srcu);
> + if (init) {
> + struct pvclock_vcpu_stolen_time init_values = {
> + .revision = 0,
> + .attributes = 0

nit: 0 is the default initialiser.

> + };
> + kvm_write_guest(kvm, base, &init_values,
> + sizeof(init_values));
> + }

I'm not convinced by this init phase right in the middle of the normal
path. It looks ugly, and it'd be better if moved out of line. I'd
suggest:

static void kvm_init_stolen_time(struct kvm_vcpu *vcpu)
{
struct pvclock_vcpu_stolen_time init_values = { };

vcpu->arch.steal.steal = 0;
vcpu->arch.steal.last_steal = current->sched_info.run_delay;

idx = srcu_read_lock(&kvm->srcu);
kvm_write_guest(kvm, base, &init_values, sizeof(init_values));
srcu_read_unlock(&kvm->srcu, idx);
}

and change the two callers accordingly. Or even better, move this code
to the hypercall handling function, because that's where it actually
belongs.

> + offset = offsetof(struct pvclock_vcpu_stolen_time, stolen_time);
> + kvm_put_guest(kvm, base + offset, steal_le, u64);
> + srcu_read_unlock(&kvm->srcu, idx);
> +
> + return 0;
> +}
> +
> long kvm_hypercall_pv_features(struct kvm_vcpu *vcpu)
> {
> u32 feature = smccc_get_arg1(vcpu);
> @@ -12,6 +49,7 @@ long kvm_hypercall_pv_features(struct kvm_vcpu *vcpu)
>
> switch (feature) {
> case ARM_SMCCC_HV_PV_TIME_FEATURES:
> + case ARM_SMCCC_HV_PV_TIME_ST:
> val = SMCCC_RET_SUCCESS;
> break;
> }
> @@ -19,3 +57,21 @@ long kvm_hypercall_pv_features(struct kvm_vcpu *vcpu)
> return val;
> }
>
> +long kvm_hypercall_stolen_time(struct kvm_vcpu *vcpu)

Why long? If that's a base address, then it is either a phys_addr_t or
a gpa_t. I'd suggest you move the error check to the caller.

> +{
> + int err;
> +
> + /*
> + * Start counting stolen time from the time the guest requests
> + * the feature enabled.
> + */
> + vcpu->arch.steal.steal = 0;
> + vcpu->arch.steal.last_steal = current->sched_info.run_delay;
> +
> + err = kvm_update_stolen_time(vcpu, true);
> +
> + if (err)
> + return SMCCC_RET_NOT_SUPPORTED;
> +
> + return vcpu->arch.steal.base;
> +}
> --
> 2.20.1
>
>

Thanks,

M.

--
Jazz is not dead, it just smells funny.