On Sat, 3 Aug 2019 18:58:17 +0100
Marc Zyngier [off-list ref] wrote:

On Fri,  2 Aug 2019 15:50:12 +0100
Steven Price [off-list ref] wrote:

quoted

Implement the service call for configuring a shared structre 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
structre 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/arm64/include/asm/kvm_host.h | 13 +++++-
 arch/arm64/kvm/Kconfig            |  1 +
 include/kvm/arm_hypercalls.h      |  1 +
 include/linux/kvm_types.h         |  2 +
 virt/kvm/arm/arm.c                | 18 ++++++++
 virt/kvm/arm/hypercalls.c         | 70 +++++++++++++++++++++++++++++++
 6 files changed, 104 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index f656169db8c3..78f270190d43 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 {
+		void *st;
+		gpa_t st_base;
+	} 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)))

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/kvm/arm_hypercalls.h b/include/kvm/arm_hypercalls.h
index 35a5abcc4ca3..9f0710ab4292 100644
--- a/include/kvm/arm_hypercalls.h
+++ b/include/kvm/arm_hypercalls.h

@@ -7,6 +7,7 @@
 #include <asm/kvm_emulate.h>
 
 int kvm_hvc_call_handler(struct kvm_vcpu *vcpu);
+int kvm_update_stolen_time(struct kvm_vcpu *vcpu);
 
 static inline u32 smccc_get_function(struct kvm_vcpu *vcpu)
 {

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 f645c0fbf7ec..ebd963d2580b 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);

@@ -371,6 +376,7 @@ 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);
+	kvm_make_request(KVM_REQ_RECORD_STEAL, vcpu);
 
 	if (single_task_running())
 		vcpu_clear_wfe_traps(vcpu);

@@ -617,6 +623,15 @@ 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);
+	srcu_read_unlock(&vcpu->kvm->srcu, idx);
+}
+
 static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu)
 {
 	return vcpu->arch.target >= 0;

@@ -636,6 +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))
+			vcpu_req_record_steal(vcpu);  

Something troubles me. Here, you've set the request on load. But you
can be preempted at any time (preemption gets disabled just after).

I have the feeling that should you get preempted right here, you'll
end-up having accumulated the wrong amount of steal time, as the
request put via load when you'll get scheduled back in will only get
processed after a full round of entry/exit/entry, which doesn't look
great.

Ah, no. We're saved by the check for pending requests right before we
jump in the guest, causing an early exit and the whole shebang to be
restarted.

	M.
-- 
Without deviation from the norm, progress is not possible.

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