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From: Marc Zyngier <maz@kernel.org>
To: Steven Price <steven.price@arm.com>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu
Cc: "Catalin Marinas" <catalin.marinas@arm.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Russell King" <linux@armlinux.org.uk>,
	"James Morse" <james.morse@arm.com>,
	"Julien Thierry" <julien.thierry.kdev@gmail.com>,
	"Suzuki K Pouloze" <suzuki.poulose@arm.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	kvm@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/9] KVM: arm64: Support stolen time reporting via shared structure
Date: Mon, 19 Aug 2019 17:40:22 +0100
Message-ID: <f6fad4fa-323d-306c-c582-de07464f4d00@kernel.org> (raw)
In-Reply-To: <20190819140436.12207-5-steven.price@arm.com>

Hi Steven,

On 19/08/2019 15:04, 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 uses WRITE_ONCE() to update the shared
> structure ensuring single copy atomicity of the 64-bit unsigned value
> that reports 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   | 15 +++++++
>  arch/arm64/include/asm/kvm_host.h | 16 ++++++-
>  arch/arm64/kvm/Kconfig            |  1 +
>  include/linux/kvm_types.h         |  2 +
>  virt/kvm/arm/arm.c                | 19 +++++++++
>  virt/kvm/arm/hypercalls.c         |  3 ++
>  virt/kvm/arm/pvtime.c             | 71 +++++++++++++++++++++++++++++++
>  7 files changed, 126 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 369b5d2d54bf..14d61a84c270 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);
>  
> @@ -77,6 +78,12 @@ struct kvm_arch {
>  
>  	/* Mandated version of PSCI */
>  	u32 psci_version;
> +
> +	struct kvm_arch_pvtime {
> +		struct gfn_to_hva_cache st_ghc;
> +		gpa_t st_base;
> +		u64 st_size;
> +	} pvtime;

It'd be good if we could avoid having this in the 32bit vcpu structure,
given that it serves no real purpose (other than being able to compile
things).

>  };
>  
>  #define KVM_NR_MEM_OBJS     40
> @@ -328,6 +335,14 @@ 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;
> +}
>  
>  void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>  
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 583b3639062a..627ecbdd0c59 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 +84,12 @@ struct kvm_arch {
>  
>  	/* Mandated version of PSCI */
>  	u32 psci_version;
> +
> +	struct kvm_arch_pvtime {
> +		struct gfn_to_hva_cache st_ghc;
> +		gpa_t st_base;
> +		u64 st_size;
> +	} pvtime;
>  };
>  
>  #define KVM_NR_MEM_OBJS     40
> @@ -338,8 +345,13 @@ 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 +491,8 @@ 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);
>  
>  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..53cc80e98d8b 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->arch.pvtime.st_base = GPA_INVALID;
>  	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 (vcpu->kvm->arch.pvtime.st_base != GPA_INVALID)
> +		kvm_make_request(KVM_REQ_RECORD_STEAL, vcpu);
>  
>  	if (single_task_running())
>  		vcpu_clear_wfe_traps(vcpu);
> @@ -625,6 +632,15 @@ static void vcpu_req_sleep(struct kvm_vcpu *vcpu)
>  	smp_rmb();
>  }
>  
> +static void vcpu_req_record_steal(struct kvm_vcpu *vcpu)
> +{
> +	int idx;
> +
> +	idx = srcu_read_lock(&vcpu->kvm->srcu);
> +	kvm_update_stolen_time(vcpu, false);
> +	srcu_read_unlock(&vcpu->kvm->srcu, idx);
> +}
> +
>  static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu)
>  {
>  	return vcpu->arch.target >= 0;
> @@ -644,6 +660,9 @@ 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))
> +			vcpu_req_record_steal(vcpu);
>  	}
>  }
>  
> 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..f169184e4076 100644
> --- a/virt/kvm/arm/pvtime.c
> +++ b/virt/kvm/arm/pvtime.c
> @@ -3,8 +3,55 @@
>  
>  #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);
> +	pagefault_disable();

What's the reason for doing a pagefault_disable()? What I'd expect is
for the userspace page to be faulted in and written to, and doing a
pagefault_disable() seems to be going against this idea.

> +	idx = srcu_read_lock(&kvm->srcu);
> +	if (init) {
> +		struct pvclock_vcpu_stolen_time init_values = {
> +			.revision = 0,
> +			.attributes = 0
> +		};
> +		kvm_write_guest_offset_cached(kvm,
> +				&pvtime->st_ghc,
> +				&init_values, offset, sizeof(init_values));
> +	}
> +	offset += offsetof(struct pvclock_vcpu_stolen_time, stolen_time);
> +	kvm_write_guest_offset_cached(kvm, &pvtime->st_ghc,
> +			&steal_le, offset, sizeof(steal_le));
> +	srcu_read_unlock(&kvm->srcu, idx);
> +	pagefault_enable();
> +
> +	return 0;
> +}
> +
>  int kvm_hypercall_pv_features(struct kvm_vcpu *vcpu)
>  {
>  	u32 feature = smccc_get_arg1(vcpu);
> @@ -12,6 +59,7 @@ 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 +67,26 @@ 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;
> +}
> 

Thanks,

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

  reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-19 14:04 [PATCH v2 0/9] arm64: Stolen time support Steven Price
2019-08-19 14:04 ` [PATCH v2 1/9] KVM: arm64: Document PV-time interface Steven Price
2019-08-19 14:04 ` [PATCH v2 2/9] KVM: arm/arm64: Factor out hypercall handling from PSCI code Steven Price
2019-08-19 14:04 ` [PATCH v2 3/9] KVM: arm64: Implement PV_FEATURES call Steven Price
2019-08-19 14:04 ` [PATCH v2 4/9] KVM: arm64: Support stolen time reporting via shared structure Steven Price
2019-08-19 16:40   ` Marc Zyngier [this message]
2019-08-21 10:27     ` Steven Price
2019-08-19 14:04 ` [PATCH v2 5/9] KVM: Allow kvm_device_ops to be const Steven Price
2019-08-19 14:04 ` [PATCH v2 6/9] KVM: arm64: Provide a PV_TIME device to user space Steven Price
2019-08-19 14:04 ` [PATCH v2 7/9] arm/arm64: Provide a wrapper for SMCCC 1.1 calls Steven Price
2019-08-19 14:04 ` [PATCH v2 8/9] arm/arm64: Make use of the SMCCC 1.1 wrapper Steven Price
2019-08-19 14:04 ` [PATCH v2 9/9] arm64: Retrieve stolen time as paravirtualized guest Steven Price

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