From 42bcbebf11dff0c2501831f1d86655eee506240f Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Thu, 10 Aug 2017 06:55:51 -0700 Subject: [PATCH] KVM: MMU: Fix softlockup due to mmu_lock is held too long MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit watchdog: BUG: soft lockup - CPU#5 stuck for 22s! [warn_test:3089] irq event stamp: 20532 hardirqs last enabled at (20531): [] restore_regs_and_iret+0x0/0x1d hardirqs last disabled at (20532): [] apic_timer_interrupt+0x98/0xb0 softirqs last enabled at (8266): [] __do_softirq+0x206/0x4c1 softirqs last disabled at (8253): [] 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. Cc: Paolo Bonzini Cc: Radim Krčmář Signed-off-by: Wanpeng Li Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 7ee21c087c83..e4ce20bee5de 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); } /* -- 2.20.1