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SubjectRe: [PATCH v3 05/10] KVM: arm64: Support stolen time reporting via shared structure
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Hi Steven,

Only one comment, at the bottom.

On 2019/8/21 23:36, Steven Price 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.
>
> The hypervisor allocates memory which is placed at an IPA 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 | 25 +++++++++++-
> arch/arm64/kvm/Kconfig | 1 +
> include/linux/kvm_types.h | 2 +
> virt/kvm/arm/arm.c | 10 +++++
> virt/kvm/arm/hypercalls.c | 3 ++
> virt/kvm/arm/pvtime.c | 67 +++++++++++++++++++++++++++++++
> 7 files changed, 127 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 369b5d2d54bf..47d2ced99421 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 int kvm_hypercall_pv_features(struct kvm_vcpu *vcpu)
> return SMCCC_RET_NOT_SUPPORTED;
> }
>
> +static inline int 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_pvtime_init_vm(struct kvm_arch *kvm_arch)
> +{
> +}
> +
> +static inline bool kvm_is_pvtime_enabled(struct kvm_arch *kvm_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 583b3639062a..b6fa7beffd8a 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);
>
> @@ -83,6 +84,11 @@ struct kvm_arch {
>
> /* Mandated version of PSCI */
> u32 psci_version;
> +
> + struct kvm_arch_pvtime {
> + gpa_t st_base;
> + u64 st_size;
> + } pvtime;
> };
>
> #define KVM_NR_MEM_OBJS 40
> @@ -338,8 +344,13 @@ 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;
> + } steal;
> +};
> /* 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 +490,18 @@ int kvm_perf_init(void);
> int kvm_perf_teardown(void);
>
> int kvm_hypercall_pv_features(struct kvm_vcpu *vcpu);
> +int kvm_hypercall_stolen_time(struct kvm_vcpu *vcpu);
> +int kvm_update_stolen_time(struct kvm_vcpu *vcpu, bool init);
> +
> +static inline void kvm_pvtime_init_vm(struct kvm_arch *kvm_arch)
> +{
> + kvm_arch->pvtime.st_base = GPA_INVALID;
> +}
> +
> +static inline bool kvm_is_pvtime_enabled(struct kvm_arch *kvm_arch)
> +{
> + return (kvm_arch->pvtime.st_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 35a069815baf..5e8343e2dd62 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
> @@ -135,6 +139,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> kvm->arch.max_vcpus = vgic_present ?
> kvm_vgic_get_max_vcpus() : KVM_MAX_VCPUS;
>
> + kvm_pvtime_init_vm(&kvm->arch);
> return ret;
> out_free_stage2_pgd:
> kvm_free_stage2_pgd(kvm);
> @@ -379,6 +384,8 @@ 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_is_pvtime_enabled(&vcpu->kvm->arch))
> + kvm_make_request(KVM_REQ_RECORD_STEAL, vcpu);
>
> if (single_task_running())
> vcpu_clear_wfe_traps(vcpu);
> @@ -644,6 +651,9 @@ 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 63ae629c466a..ac678eabf15f 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_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 6201d71cb1f8..28603689f6e0 100644
> --- a/virt/kvm/arm/pvtime.c
> +++ b/virt/kvm/arm/pvtime.c
> @@ -3,8 +3,51 @@
>
> #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;
> + struct kvm_arch_pvtime *pvtime = &kvm->arch.pvtime;
> + u64 steal;
> + u64 steal_le;
> + u64 offset;
> + int idx;
> + const int stride = sizeof(struct pvclock_vcpu_stolen_time);
> +
> + if (pvtime->st_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;
> +
> + offset = stride * kvm_vcpu_get_idx(vcpu);
> +
> + if (unlikely(offset + stride > pvtime->st_size))
> + return -EINVAL;
> +
> + 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
> + };
> + kvm_write_guest(kvm, pvtime->st_base + offset, &init_values,
> + sizeof(init_values));
> + }
> + offset += offsetof(struct pvclock_vcpu_stolen_time, stolen_time);
> + kvm_put_guest(kvm, pvtime->st_base + offset, steal_le, u64);
> + srcu_read_unlock(&kvm->srcu, idx);
> +
> + return 0;
> +}
> +
> int kvm_hypercall_pv_features(struct kvm_vcpu *vcpu)
> {
> u32 feature = smccc_get_arg1(vcpu);
> @@ -12,6 +55,7 @@ int kvm_hypercall_pv_features(struct kvm_vcpu *vcpu)
>
> switch (feature) {
> case ARM_SMCCC_HV_PV_FEATURES:
> + case ARM_SMCCC_HV_PV_TIME_ST:
> val = SMCCC_RET_SUCCESS;
> break;
> }
> @@ -19,3 +63,26 @@ int kvm_hypercall_pv_features(struct kvm_vcpu *vcpu)
> return val;
> }
>
> +int kvm_hypercall_stolen_time(struct kvm_vcpu *vcpu)
> +{
> + u64 ret;
> + 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)
> + ret = SMCCC_RET_NOT_SUPPORTED;
> + else
> + ret = vcpu->kvm->arch.pvtime.st_base +
> + (sizeof(struct pvclock_vcpu_stolen_time) *
> + kvm_vcpu_get_idx(vcpu));
> +
> + return ret;

The *type* of the 'ret' here looks a bit messy to me:
(1)u64 -> (2)int -> (3)u32 -> (4)unsigned long

(1)->(2): just inside kvm_hypercall_stolen_time()
(2)->(3): inside kvm_hvc_call_handler(), assign 'ret' to 'val'
(3)->(4): through smccc_set_retval()

I really have seen an issue caused by (2)->(3).

When the PV guest running without PV_TIME device supporting, the result
of the ARM_SMCCC_HV_PV_TIME_ST hypercall is expected to be -1 (which
means "not supported"), but the actual result I got is 4294967295.
Guest continues to run blindly, bad things would happen then...

I think this needs a fix?


Thanks,
zenghui

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