From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
watchdog: BUG: soft lockup - CPU#5 stuck for 22s! [warn_test:3089]
irq event stamp: 20532
hardirqs last enabled at (20531): [<ffffffff8e9b6908>] restore_regs_and_iret+0x0/0x1d
hardirqs last disabled at (20532): [<ffffffff8e9b7ae8>] apic_timer_interrupt+0x98/0xb0
softirqs last enabled at (8266): [<ffffffff8e9badc6>] __do_softirq+0x206/0x4c1
softirqs last disabled at (8253): [<ffffffff8e083918>] irq_exit+0xf8/0x100
CPU: 5 PID: 3089 Comm: warn_test Tainted: G OE 4.13.0-rc3+ #8
RIP: 0010:kvm_mmu_prepare_zap_page+0x72/0x4b0 [kvm]
Call Trace:
make_mmu_pages_available.isra.120+0x71/0xc0 [kvm]
kvm_mmu_load+0x1cf/0x410 [kvm]
kvm_arch_vcpu_ioctl_run+0x1316/0x1bf0 [kvm]
kvm_vcpu_ioctl+0x340/0x700 [kvm]
? kvm_vcpu_ioctl+0x340/0x700 [kvm]
? __fget+0xfc/0x210
do_vfs_ioctl+0xa4/0x6a0
? __fget+0x11d/0x210
SyS_ioctl+0x79/0x90
entry_SYSCALL_64_fastpath+0x23/0xc2
? __this_cpu_preempt_check+0x13/0x20
This can be reproduced readily by ept=N and running syzkaller tests since
many syzkaller testcases don't setup any memory regions. However, if ept=Y
rmode identity map will be created, then kvm_mmu_calculate_mmu_pages() will
extend the number of VM's mmu pages to at least KVM_MIN_ALLOC_MMU_PAGES
which just hide the issue.
I saw the scenario kvm->arch.n_max_mmu_pages == 0 && kvm->arch.n_used_mmu_pages == 1,
so there is one active mmu page on the list, kvm_mmu_prepare_zap_page() fails
to zap any pages, however prepare_zap_oldest_mmu_page() always returns true.
It incurs infinite loop in make_mmu_pages_available() which causes mmu->lock
softlockup.
This patch fixes it by setting the return value of prepare_zap_oldest_mmu_page()
according to whether or not there is mmu page zapped. In addition, we bail out
immediately if there is no available mmu page to alloc root page.
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
---
arch/x86/kvm/mmu.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 9b1dd11..b9897e8 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2608,9 +2608,7 @@ static bool prepare_zap_oldest_mmu_page(struct kvm *kvm,
sp = list_last_entry(&kvm->arch.active_mmu_pages,
struct kvm_mmu_page, link);
- kvm_mmu_prepare_zap_page(kvm, sp, invalid_list);
-
- return true;
+ return kvm_mmu_prepare_zap_page(kvm, sp, invalid_list);
}
/*
@@ -3379,6 +3377,10 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
if (vcpu->arch.mmu.shadow_root_level == PT64_ROOT_LEVEL) {
spin_lock(&vcpu->kvm->mmu_lock);
make_mmu_pages_available(vcpu);
+ if (!kvm_mmu_available_pages(vcpu->kvm)) {
+ spin_unlock(&vcpu->kvm->mmu_lock);
+ return 1;
+ }
sp = kvm_mmu_get_page(vcpu, 0, 0, PT64_ROOT_LEVEL, 1, ACC_ALL);
++sp->root_count;
spin_unlock(&vcpu->kvm->mmu_lock);
@@ -3390,6 +3392,10 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
MMU_WARN_ON(VALID_PAGE(root));
spin_lock(&vcpu->kvm->mmu_lock);
make_mmu_pages_available(vcpu);
+ if (!kvm_mmu_available_pages(vcpu->kvm)) {
+ spin_unlock(&vcpu->kvm->mmu_lock);
+ return 1;
+ }
sp = kvm_mmu_get_page(vcpu, i << (30 - PAGE_SHIFT),
i << 30, PT32_ROOT_LEVEL, 1, ACC_ALL);
root = __pa(sp->spt);
@@ -3427,6 +3433,10 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
spin_lock(&vcpu->kvm->mmu_lock);
make_mmu_pages_available(vcpu);
+ if (!kvm_mmu_available_pages(vcpu->kvm)) {
+ spin_unlock(&vcpu->kvm->mmu_lock);
+ return 1;
+ }
sp = kvm_mmu_get_page(vcpu, root_gfn, 0, PT64_ROOT_LEVEL,
0, ACC_ALL);
root = __pa(sp->spt);
--
2.7.4
