From 8f902b005ece690f0f50b217975601b804905dc8 Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Fri, 20 Mar 2015 20:39:38 +1100 Subject: [PATCH] KVM: PPC: Book3S HV: Fix spinlock/mutex ordering issue in kvmppc_set_lpcr() Currently, kvmppc_set_lpcr() has a spinlock around the whole function, and inside that does mutex_lock(&kvm->lock). It is not permitted to take a mutex while holding a spinlock, because the mutex_lock might call schedule(). In addition, this causes lockdep to warn about a lock ordering issue: ====================================================== [ INFO: possible circular locking dependency detected ] 3.18.0-kvm-04645-gdfea862-dirty #131 Not tainted ------------------------------------------------------- qemu-system-ppc/8179 is trying to acquire lock: (&kvm->lock){+.+.+.}, at: [] .kvmppc_set_lpcr+0xf4/0x1c0 [kvm_hv] but task is already holding lock: (&(&vcore->lock)->rlock){+.+...}, at: [] .kvmppc_set_lpcr+0x40/0x1c0 [kvm_hv] which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&(&vcore->lock)->rlock){+.+...}: [] .mutex_lock_nested+0x80/0x570 [] .kvmppc_vcpu_run_hv+0xc4/0xe40 [kvm_hv] [] .kvmppc_vcpu_run+0x2c/0x40 [kvm] [] .kvm_arch_vcpu_ioctl_run+0x54/0x160 [kvm] [] .kvm_vcpu_ioctl+0x4a8/0x7b0 [kvm] [] .do_vfs_ioctl+0x444/0x770 [] .SyS_ioctl+0xc4/0xe0 [] syscall_exit+0x0/0x98 -> #0 (&kvm->lock){+.+.+.}: [] .lock_acquire+0xcc/0x1a0 [] .mutex_lock_nested+0x80/0x570 [] .kvmppc_set_lpcr+0xf4/0x1c0 [kvm_hv] [] .kvmppc_set_one_reg_hv+0x4dc/0x990 [kvm_hv] [] .kvmppc_set_one_reg+0x44/0x330 [kvm] [] .kvm_vcpu_ioctl_set_one_reg+0x5c/0x150 [kvm] [] .kvm_arch_vcpu_ioctl+0x214/0x2c0 [kvm] [] .kvm_vcpu_ioctl+0xe0/0x7b0 [kvm] [] .do_vfs_ioctl+0x444/0x770 [] .SyS_ioctl+0xc4/0xe0 [] syscall_exit+0x0/0x98 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&(&vcore->lock)->rlock); lock(&kvm->lock); lock(&(&vcore->lock)->rlock); lock(&kvm->lock); *** DEADLOCK *** 2 locks held by qemu-system-ppc/8179: #0: (&vcpu->mutex){+.+.+.}, at: [] .vcpu_load+0x28/0x90 [kvm] #1: (&(&vcore->lock)->rlock){+.+...}, at: [] .kvmppc_set_lpcr+0x40/0x1c0 [kvm_hv] stack backtrace: CPU: 4 PID: 8179 Comm: qemu-system-ppc Not tainted 3.18.0-kvm-04645-gdfea862-dirty #131 Call Trace: [c000001a66c0f310] [c000000000b486ac] .dump_stack+0x88/0xb4 (unreliable) [c000001a66c0f390] [c0000000000f8bec] .print_circular_bug+0x27c/0x3d0 [c000001a66c0f440] [c0000000000fe9e8] .__lock_acquire+0x2028/0x2190 [c000001a66c0f5d0] [c0000000000ff28c] .lock_acquire+0xcc/0x1a0 [c000001a66c0f6a0] [c000000000b3c120] .mutex_lock_nested+0x80/0x570 [c000001a66c0f7c0] [d00000000ecc1f54] .kvmppc_set_lpcr+0xf4/0x1c0 [kvm_hv] [c000001a66c0f860] [d00000000ecc510c] .kvmppc_set_one_reg_hv+0x4dc/0x990 [kvm_hv] [c000001a66c0f8d0] [d00000000eb9f234] .kvmppc_set_one_reg+0x44/0x330 [kvm] [c000001a66c0f960] [d00000000eb9c9dc] .kvm_vcpu_ioctl_set_one_reg+0x5c/0x150 [kvm] [c000001a66c0f9f0] [d00000000eb9ced4] .kvm_arch_vcpu_ioctl+0x214/0x2c0 [kvm] [c000001a66c0faf0] [d00000000eb940b0] .kvm_vcpu_ioctl+0xe0/0x7b0 [kvm] [c000001a66c0fcb0] [c00000000026cbb4] .do_vfs_ioctl+0x444/0x770 [c000001a66c0fd90] [c00000000026cfa4] .SyS_ioctl+0xc4/0xe0 [c000001a66c0fe30] [c000000000009264] syscall_exit+0x0/0x98 This fixes it by moving the mutex_lock()/mutex_unlock() pair outside the spin-locked region. Signed-off-by: Paul Mackerras Signed-off-by: Alexander Graf --- arch/powerpc/kvm/book3s_hv.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index de4018a1bc4bd2..b2731933f80775 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -942,20 +942,20 @@ static int kvm_arch_vcpu_ioctl_set_sregs_hv(struct kvm_vcpu *vcpu, static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr, bool preserve_top32) { + struct kvm *kvm = vcpu->kvm; struct kvmppc_vcore *vc = vcpu->arch.vcore; u64 mask; + mutex_lock(&kvm->lock); spin_lock(&vc->lock); /* * If ILE (interrupt little-endian) has changed, update the * MSR_LE bit in the intr_msr for each vcpu in this vcore. */ if ((new_lpcr & LPCR_ILE) != (vc->lpcr & LPCR_ILE)) { - struct kvm *kvm = vcpu->kvm; struct kvm_vcpu *vcpu; int i; - mutex_lock(&kvm->lock); kvm_for_each_vcpu(i, vcpu, kvm) { if (vcpu->arch.vcore != vc) continue; @@ -964,7 +964,6 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr, else vcpu->arch.intr_msr &= ~MSR_LE; } - mutex_unlock(&kvm->lock); } /* @@ -981,6 +980,7 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr, mask &= 0xFFFFFFFF; vc->lpcr = (vc->lpcr & ~mask) | (new_lpcr & mask); spin_unlock(&vc->lock); + mutex_unlock(&kvm->lock); } static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,