On 05/12/2017 07:21, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> The below test case can cause infinite loop in kvm when ept=0.
>
> #include <unistd.h>
> #include <sys/syscall.h>
> #include <string.h>
> #include <stdint.h>
> #include <linux/kvm.h>
> #include <fcntl.h>
> #include <sys/ioctl.h>
>
> long r[5];
> int main()
> {
> r[2] = open("/dev/kvm", O_RDONLY);
> r[3] = ioctl(r[2], KVM_CREATE_VM, 0);
> r[4] = ioctl(r[3], KVM_CREATE_VCPU, 7);
> ioctl(r[4], KVM_RUN, 0);
> }
>
> It doesn't setup the memory regions, mmu_alloc_shadow/direct_roots() in
> kvm return 1 when kvm fails to allocate root page table which can result
> in beblow infinite loop:
>
> vcpu_run() {
> for (;;) {
> r = vcpu_enter_guest()::kvm_mmu_reload() returns 1
> if (r <= 0)
> break;
> if (need_resched())
> cond_resched();
> }
> }
>
> This patch fixes it by returning -ENOSPC when there is no available kvm mmu
> page for root page table.
>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Fixes: 26eeb53cf0f (KVM: MMU: Bail out immediately if there is no available mmu page)
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index c9aaa18..89da688 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3395,7 +3395,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
> spin_lock(&vcpu->kvm->mmu_lock);
> if(make_mmu_pages_available(vcpu) < 0) {
> spin_unlock(&vcpu->kvm->mmu_lock);
> - return 1;
> + return -ENOSPC;
> }
> sp = kvm_mmu_get_page(vcpu, 0, 0,
> vcpu->arch.mmu.shadow_root_level, 1, ACC_ALL);
> @@ -3410,7 +3410,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
> spin_lock(&vcpu->kvm->mmu_lock);
> if (make_mmu_pages_available(vcpu) < 0) {
> spin_unlock(&vcpu->kvm->mmu_lock);
> - return 1;
> + return -ENOSPC;
> }
> sp = kvm_mmu_get_page(vcpu, i << (30 - PAGE_SHIFT),
> i << 30, PT32_ROOT_LEVEL, 1, ACC_ALL);
> @@ -3450,7 +3450,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
> spin_lock(&vcpu->kvm->mmu_lock);
> if (make_mmu_pages_available(vcpu) < 0) {
> spin_unlock(&vcpu->kvm->mmu_lock);
> - return 1;
> + return -ENOSPC;
> }
> sp = kvm_mmu_get_page(vcpu, root_gfn, 0,
> vcpu->arch.mmu.shadow_root_level, 0, ACC_ALL);
> @@ -3487,7 +3487,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
> spin_lock(&vcpu->kvm->mmu_lock);
> if (make_mmu_pages_available(vcpu) < 0) {
> spin_unlock(&vcpu->kvm->mmu_lock);
> - return 1;
> + return -ENOSPC;
> }
> sp = kvm_mmu_get_page(vcpu, root_gfn, i << 30, PT32_ROOT_LEVEL,
> 0, ACC_ALL);
>
Queued, thanks.
