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Reported by syzkaller: The kvm-intel.unrestricted_guest=0 WARNING: CPU: 5 PID: 1014 at /home/kernel/data/kvm/arch/x86/kvm//x86.c:7227 kvm_arch_vcpu_ioctl_run+0x38b/0x1be0 [kvm] CPU: 5 PID: 1014 Comm: warn_test Tainted: G W OE 4.13.0-rc3+ #8 RIP: 0010:kvm_arch_vcpu_ioctl_run+0x38b/0x1be0 [kvm] Call Trace: ? put_pid+0x3a/0x50 ? rcu_read_lock_sched_held+0x79/0x80 ? kmem_cache_free+0x2f2/0x350 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 The syszkaller folks reported a residual mmio emulation request to userspace due to vm86 fails to emulate inject real mode interrupt(fails to read CS) and incurs a triple fault. The vCPU returns to userspace with vcpu->mmio_needed == true and KVM_EXIT_SHUTDOWN exit reason. However, the syszkaller testcase constructs several threads to launch the same vCPU, the thread which lauch this vCPU after the thread whichs get the vcpu->mmio_needed == true and KVM_EXIT_SHUTDOWN will trigger the warning. #define _GNU_SOURCE #include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/wait.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/mman.h> #include <fcntl.h> #include <unistd.h> #include <linux/kvm.h> #include <stdio.h> int kvmcpu; struct kvm_run *run; void* thr(void* arg) { int res; res = ioctl(kvmcpu, KVM_RUN, 0); printf("ret1=%d exit_reason=%d suberror=%d\n", res, run->exit_reason, run->internal.suberror); return 0; } void test() { int i, kvm, kvmvm; pthread_t th[4]; kvm = open("/dev/kvm", O_RDWR); kvmvm = ioctl(kvm, KVM_CREATE_VM, 0); kvmcpu = ioctl(kvmvm, KVM_CREATE_VCPU, 0); run = (struct kvm_run*)mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, kvmcpu, 0); srand(getpid()); for (i = 0; i < 4; i++) { pthread_create(&th[i], 0, thr, 0); usleep(rand() % 10000); } for (i = 0; i < 4; i++) pthread_join(th[i], 0); } int main() { for (;;) { int pid = fork(); if (pid < 0) exit(1); if (pid == 0) { test(); exit(0); } int status; while (waitpid(pid, &status, __WALL) != pid) {} } return 0; } This patch fixes it by resetting the vcpu->mmio_needed once we receive the triple fault to avoid the residue. Reported-by: Dmitry Vyukov <dvyukov@google.com> Tested-by: Dmitry Vyukov <dvyukov@google.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.