[PATCH v7 2/4] KVM: x86: Dirty quota-based throttling of vcpus

[Shivam Kumar <shivam.kumar1@xxxxxxxxxxx>]

Exit to userspace whenever the dirty quota is exhausted (i.e. dirty count
equals/exceeds dirty quota) to request more dirty quota.

Suggested-by: Shaju Abraham <shaju.abraham@xxxxxxxxxxx>
Suggested-by: Manish Mishra <manish.mishra@xxxxxxxxxxx>
Co-developed-by: Anurag Madnawat <anurag.madnawat@xxxxxxxxxxx>
Signed-off-by: Anurag Madnawat <anurag.madnawat@xxxxxxxxxxx>
Signed-off-by: Shivam Kumar <shivam.kumar1@xxxxxxxxxxx>
---
 arch/x86/kvm/mmu/spte.c |  4 ++--
 arch/x86/kvm/vmx/vmx.c  |  3 +++
 arch/x86/kvm/x86.c      | 28 ++++++++++++++++++++++++++++
 3 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index 2e08b2a45361..c0ed35abbf2d 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -228,9 +228,9 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
 		  "spte = 0x%llx, level = %d, rsvd bits = 0x%llx", spte, level,
 		  get_rsvd_bits(&vcpu->arch.mmu->shadow_zero_check, spte, level));
 
-	if ((spte & PT_WRITABLE_MASK) && kvm_slot_dirty_track_enabled(slot)) {
+	if (spte & PT_WRITABLE_MASK) {
 		/* Enforced by kvm_mmu_hugepage_adjust. */
-		WARN_ON(level > PG_LEVEL_4K);
+		WARN_ON(level > PG_LEVEL_4K && kvm_slot_dirty_track_enabled(slot));
 		mark_page_dirty_in_slot(vcpu->kvm, slot, gfn);
 	}
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 63247c57c72c..cc130999eddf 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5745,6 +5745,9 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
 		 */
 		if (__xfer_to_guest_mode_work_pending())
 			return 1;
+
+		if (kvm_test_request(KVM_REQ_DIRTY_QUOTA_EXIT, vcpu))
+			return 1;
 	}
 
 	return 1;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ecea83f0da49..1a960fbb51f4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10494,6 +10494,30 @@ void __kvm_request_immediate_exit(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(__kvm_request_immediate_exit);
 
+static inline bool kvm_check_dirty_quota_request(struct kvm_vcpu *vcpu)
+{
+#ifdef CONFIG_HAVE_KVM_DIRTY_QUOTA
+	struct kvm_run *run;
+
+	if (kvm_check_request(KVM_REQ_DIRTY_QUOTA_EXIT, vcpu)) {
+		run = vcpu->run;
+		run->exit_reason = KVM_EXIT_DIRTY_QUOTA_EXHAUSTED;
+		run->dirty_quota_exit.count = vcpu->stat.generic.pages_dirtied;
+		run->dirty_quota_exit.quota = READ_ONCE(run->dirty_quota);
+
+		/*
+		 * Re-check the quota and exit if and only if the vCPU still
+		 * exceeds its quota.  If userspace increases (or disables
+		 * entirely) the quota, then no exit is required as KVM is
+		 * still honoring its ABI, e.g. userspace won't even be aware
+		 * that KVM temporarily detected an exhausted quota.
+		 */
+		return run->dirty_quota_exit.count >= run->dirty_quota_exit.quota;
+	}
+#endif
+	return false;
+}
+
 /*
  * Called within kvm->srcu read side.
  * Returns 1 to let vcpu_run() continue the guest execution loop without
@@ -10625,6 +10649,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 			r = 0;
 			goto out;
 		}
+		if (kvm_check_dirty_quota_request(vcpu)) {
+			r = 0;
+			goto out;
+		}
 
 		/*
 		 * KVM_REQ_HV_STIMER has to be processed after
-- 
2.22.3