On 10/08/2017 15:55, Wanpeng Li wrote:
> 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.
Nice!
But I think all callers of make_mmu_pages_available should be handled
the same way. I'm committing the first hunk for now. In the meanwhile,
can you look into returning -ENOSPC from make_mmu_pages_available if
!kvm_mmu_available_pages after zapping the pages?
Thanks,
Paolo
> 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);
>
