Merge tag 'kvm-s390-next-6.17-1' of https://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux into HEAD

RCU wakeup fix for KVM s390 guest entry

Author: bonzini

arch/s390/include/asm/entry-common.h

@@ -59,4 +59,14 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
 
 #define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare
 
+static __always_inline bool arch_in_rcu_eqs(void)
+{
+	if (IS_ENABLED(CONFIG_KVM))
+		return current->flags & PF_VCPU;
+
+	return false;
+}
+
+#define arch_in_rcu_eqs arch_in_rcu_eqs
+
 #endif

arch/s390/include/asm/kvm_host.h

@@ -716,6 +716,9 @@ extern char sie_exit;
 bool kvm_s390_pv_is_protected(struct kvm *kvm);
 bool kvm_s390_pv_cpu_is_protected(struct kvm_vcpu *vcpu);
 
+extern int kvm_s390_enter_exit_sie(struct kvm_s390_sie_block *scb,
+				   u64 *gprs, unsigned long gasce);
+
 extern int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc);
 extern int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc);
 

arch/s390/kvm/kvm-s390.c

@@ -5062,6 +5062,30 @@ static int vcpu_post_run(struct kvm_vcpu *vcpu, int exit_reason)
 	return vcpu_post_run_handle_fault(vcpu);
 }
 
+int noinstr kvm_s390_enter_exit_sie(struct kvm_s390_sie_block *scb,
+				    u64 *gprs, unsigned long gasce)
+{
+	int ret;
+
+	guest_state_enter_irqoff();
+
+	/*
+	 * The guest_state_{enter,exit}_irqoff() functions inform lockdep and
+	 * tracing that entry to the guest will enable host IRQs, and exit from
+	 * the guest will disable host IRQs.
+	 *
+	 * We must not use lockdep/tracing/RCU in this critical section, so we
+	 * use the low-level arch_local_irq_*() helpers to enable/disable IRQs.
+	 */
+	arch_local_irq_enable();
+	ret = sie64a(scb, gprs, gasce);
+	arch_local_irq_disable();
+
+	guest_state_exit_irqoff();
+
+	return ret;
+}
+
 #define PSW_INT_MASK (PSW_MASK_EXT | PSW_MASK_IO | PSW_MASK_MCHECK)
 static int __vcpu_run(struct kvm_vcpu *vcpu)
 {
@@ -5082,20 +5106,27 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 		kvm_vcpu_srcu_read_unlock(vcpu);
 		/*
 		 * As PF_VCPU will be used in fault handler, between
-		 * guest_enter and guest_exit should be no uaccess.
+		 * guest_timing_enter_irqoff and guest_timing_exit_irqoff
+		 * should be no uaccess.
 		 */
-		local_irq_disable();
-		guest_enter_irqoff();
-		__disable_cpu_timer_accounting(vcpu);
-		local_irq_enable();
 		if (kvm_s390_pv_cpu_is_protected(vcpu)) {
 			memcpy(sie_page->pv_grregs,
 			       vcpu->run->s.regs.gprs,
 			       sizeof(sie_page->pv_grregs));
 		}
-		exit_reason = sie64a(vcpu->arch.sie_block,
-				     vcpu->run->s.regs.gprs,
-				     vcpu->arch.gmap->asce);
+
+		local_irq_disable();
+		guest_timing_enter_irqoff();
+		__disable_cpu_timer_accounting(vcpu);
+
+		exit_reason = kvm_s390_enter_exit_sie(vcpu->arch.sie_block,
+						      vcpu->run->s.regs.gprs,
+						      vcpu->arch.gmap->asce);
+
+		__enable_cpu_timer_accounting(vcpu);
+		guest_timing_exit_irqoff();
+		local_irq_enable();
+
 		if (kvm_s390_pv_cpu_is_protected(vcpu)) {
 			memcpy(vcpu->run->s.regs.gprs,
 			       sie_page->pv_grregs,
@@ -5111,10 +5142,6 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 				vcpu->arch.sie_block->gpsw.mask &= ~PSW_INT_MASK;
 			}
 		}
-		local_irq_disable();
-		__enable_cpu_timer_accounting(vcpu);
-		guest_exit_irqoff();
-		local_irq_enable();
 		kvm_vcpu_srcu_read_lock(vcpu);
 
 		rc = vcpu_post_run(vcpu, exit_reason);

arch/s390/kvm/vsie.c

@@ -1170,10 +1170,6 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 	    vcpu->arch.sie_block->fpf & FPF_BPBC)
 		set_thread_flag(TIF_ISOLATE_BP_GUEST);
 
-	local_irq_disable();
-	guest_enter_irqoff();
-	local_irq_enable();
-
 	/*
 	 * Simulate a SIE entry of the VCPU (see sie64a), so VCPU blocking
 	 * and VCPU requests also hinder the vSIE from running and lead
@@ -1183,15 +1179,16 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 	vcpu->arch.sie_block->prog0c |= PROG_IN_SIE;
 	current->thread.gmap_int_code = 0;
 	barrier();
-	if (!kvm_s390_vcpu_sie_inhibited(vcpu))
-		rc = sie64a(scb_s, vcpu->run->s.regs.gprs, vsie_page->gmap->asce);
+	if (!kvm_s390_vcpu_sie_inhibited(vcpu)) {
+		local_irq_disable();
+		guest_timing_enter_irqoff();
+		rc = kvm_s390_enter_exit_sie(scb_s, vcpu->run->s.regs.gprs, vsie_page->gmap->asce);
+		guest_timing_exit_irqoff();
+		local_irq_enable();
+	}
 	barrier();
 	vcpu->arch.sie_block->prog0c &= ~PROG_IN_SIE;
 
-	local_irq_disable();
-	guest_exit_irqoff();
-	local_irq_enable();
-
 	/* restore guest state for bp isolation override */
 	if (!guest_bp_isolation)
 		clear_thread_flag(TIF_ISOLATE_BP_GUEST);

include/linux/entry-common.h

@@ -86,6 +86,22 @@ static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs);
 static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs) {}
 #endif
 
+/**
+ * arch_in_rcu_eqs - Architecture specific check for RCU extended quiescent
+ * states.
+ *
+ * Returns: true if the CPU is potentially in an RCU EQS, false otherwise.
+ *
+ * Architectures only need to define this if threads other than the idle thread
+ * may have an interruptible EQS. This does not need to handle idle threads. It
+ * is safe to over-estimate at the cost of redundant RCU management work.
+ *
+ * Invoked from irqentry_enter()
+ */
+#ifndef arch_in_rcu_eqs
+static __always_inline bool arch_in_rcu_eqs(void) { return false; }
+#endif
+
 /**
  * enter_from_user_mode - Establish state when coming from user mode
  *

kernel/entry/common.c

@@ -220,7 +220,8 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
 	 * TINY_RCU does not support EQS, so let the compiler eliminate
 	 * this part when enabled.
 	 */
-	if (!IS_ENABLED(CONFIG_TINY_RCU) && is_idle_task(current)) {
+	if (!IS_ENABLED(CONFIG_TINY_RCU) &&
+	    (is_idle_task(current) || arch_in_rcu_eqs())) {
 		/*
 		 * If RCU is not watching then the same careful
 		 * sequence vs. lockdep and tracing is required