[PATCH] RISC-V: KVM: Use a raw lock for IMSIC wakeup state

[Andrew Jones]

kvm_riscv_vcpu_aia_imsic_put() can run from the scheduler preemption
notifier while the raw runqueue lock is held. Taking vsfile_lock, an
rwlock_t, there violates the lockdep wait-context rules.

Protect the CPU/HGEI pair with a separate raw spinlock. All updates to
that pair retain vsfile_lock and take the new lock, while scheduler-out
uses only the new lock around the HGEIE update. This keeps the wakeup
setup serialized with VS-file publication and release without bringing
wider IMSIC operations into a raw critical section.

Fixes: 4cec89db80ba ("RISC-V: KVM: Move HGEI[E|P] CSR access to IMSIC virtualization")
Signed-off-by: Andrew Jones <andrew.jones@xxxxxxxxxxxxxxxx>
---
 arch/riscv/kvm/aia_imsic.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/kvm/aia_imsic.c b/arch/riscv/kvm/aia_imsic.c
index c1af23e79ae0..1ccb7eac9f45 100644
--- a/arch/riscv/kvm/aia_imsic.c
+++ b/arch/riscv/kvm/aia_imsic.c
@@ -48,6 +48,8 @@ struct imsic {
 
 	/* IMSIC VS-file */
 	rwlock_t vsfile_lock;
+	/* Writers hold both locks; scheduler-out only takes hgei_lock. */
+	raw_spinlock_t hgei_lock;
 	int vsfile_cpu;
 	int vsfile_hgei;
 	void __iomem *vsfile_va;
@@ -582,6 +584,17 @@ static void imsic_vsfile_local_update(int vsfile_hgei, u32 nr_eix,
 	csr_write(CSR_VSISELECT, old_vsiselect);
 }
 
+static void imsic_vsfile_set_hgei(struct imsic *imsic, int cpu, int hgei)
+{
+	unsigned long flags;
+
+	/* Serialize the CPU/HGEI pair with scheduler-out's wakeup setup. */
+	raw_spin_lock_irqsave(&imsic->hgei_lock, flags);
+	imsic->vsfile_cpu = cpu;
+	imsic->vsfile_hgei = hgei;
+	raw_spin_unlock_irqrestore(&imsic->hgei_lock, flags);
+}
+
 static void imsic_vsfile_cleanup(struct imsic *imsic)
 {
 	int old_vsfile_hgei, old_vsfile_cpu;
@@ -596,7 +609,7 @@ static void imsic_vsfile_cleanup(struct imsic *imsic)
 	write_lock_irqsave(&imsic->vsfile_lock, flags);
 	old_vsfile_hgei = imsic->vsfile_hgei;
 	old_vsfile_cpu = imsic->vsfile_cpu;
-	imsic->vsfile_cpu = imsic->vsfile_hgei = -1;
+	imsic_vsfile_set_hgei(imsic, -1, -1);
 	imsic->vsfile_va = NULL;
 	imsic->vsfile_pa = 0;
 	write_unlock_irqrestore(&imsic->vsfile_lock, flags);
@@ -727,10 +740,10 @@ void kvm_riscv_vcpu_aia_imsic_put(struct kvm_vcpu *vcpu)
 	if (!kvm_vcpu_is_blocking(vcpu))
 		return;
 
-	read_lock_irqsave(&imsic->vsfile_lock, flags);
+	raw_spin_lock_irqsave(&imsic->hgei_lock, flags);
 	if (imsic->vsfile_cpu > -1)
 		csr_set(CSR_HGEIE, BIT(imsic->vsfile_hgei));
-	read_unlock_irqrestore(&imsic->vsfile_lock, flags);
+	raw_spin_unlock_irqrestore(&imsic->hgei_lock, flags);
 }
 
 void kvm_riscv_vcpu_aia_imsic_release(struct kvm_vcpu *vcpu)
@@ -747,7 +760,7 @@ void kvm_riscv_vcpu_aia_imsic_release(struct kvm_vcpu *vcpu)
 	write_lock_irqsave(&imsic->vsfile_lock, flags);
 	old_vsfile_hgei = imsic->vsfile_hgei;
 	old_vsfile_cpu = imsic->vsfile_cpu;
-	imsic->vsfile_cpu = imsic->vsfile_hgei = -1;
+	imsic_vsfile_set_hgei(imsic, -1, -1);
 	imsic->vsfile_va = NULL;
 	imsic->vsfile_pa = 0;
 	write_unlock_irqrestore(&imsic->vsfile_lock, flags);
@@ -861,8 +874,7 @@ int kvm_riscv_vcpu_aia_imsic_update(struct kvm_vcpu *vcpu)
 
 	/* Update new IMSIC VS-file details in IMSIC context */
 	write_lock_irqsave(&imsic->vsfile_lock, flags);
-	imsic->vsfile_hgei = new_vsfile_hgei;
-	imsic->vsfile_cpu = vcpu->cpu;
+	imsic_vsfile_set_hgei(imsic, vcpu->cpu, new_vsfile_hgei);
 	imsic->vsfile_va = new_vsfile_va;
 	imsic->vsfile_pa = new_vsfile_pa;
 	write_unlock_irqrestore(&imsic->vsfile_lock, flags);
@@ -1112,6 +1124,7 @@ int kvm_riscv_vcpu_aia_imsic_init(struct kvm_vcpu *vcpu)
 	/* Setup IMSIC context  */
 	imsic->nr_msis = kvm->arch.aia.nr_ids + 1;
 	rwlock_init(&imsic->vsfile_lock);
+	raw_spin_lock_init(&imsic->hgei_lock);
 	imsic->nr_eix = BITS_TO_U64(imsic->nr_msis);
 	imsic->nr_hw_eix = BITS_TO_U64(kvm_riscv_aia_max_ids);
 	imsic->vsfile_hgei = imsic->vsfile_cpu = -1;
-- 
2.43.0