https://bugzilla.kernel.org/show_bug.cgi?id=103141 Alex Lyakas (alex@xxxxxxxxxx) changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |alex@xxxxxxxxxx --- Comment #4 from Alex Lyakas (alex@xxxxxxxxxx) --- We hit the same issue with kernel 3.18.19. After some debugging, I see that the first test program that felix attached, causes kvm_x86_ops->vcpu_create to return -EEXIST instead of a valid vcpu pointer. As a result, the call to kvm_x86_ops->fpu_activate tries to access an invalid pointer, and causes a NULL pointer dereference. The suggested fix was delivered in kernel 4.2. Although it was tagged as "stable", I don't see that it was backported to earlier kernels. I believe that the fix addresses a different issue, in which the vcpu pointer is valid, but further VMCS write has a problem (this is my understanding). But, of course, this fix will address also the issue that felix reported. Although for the latter, a simpler fix would suffice: --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7012,20 +7012,24 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id) { struct kvm_vcpu *vcpu; if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0) printk_once(KERN_WARNING "kvm: SMP vm created on host with unstable TSC; " "guest TSC will not be reliable\n"); vcpu = kvm_x86_ops->vcpu_create(kvm, id); + if (IS_ERR(vcpu)) { + pr_err("kvm_x86_ops->vcpu_create id=%u err=%ld\n", id, PTR_ERR(vcpu)); + return vcpu; + } /* * Activate fpu unconditionally in case the guest needs eager FPU. It will be * deactivated soon if it doesn't. */ kvm_x86_ops->fpu_activate(vcpu); return vcpu; } -- You are receiving this mail because: You are watching the assignee of the bug.
