423ecfea77
Make a KVM_REQ_APICV_UPDATE request when creating a vCPU with an in-kernel local APIC and APICv enabled at the module level. Consuming kvm_apicv_activated() and stuffing vcpu->arch.apicv_active directly can race with __kvm_set_or_clear_apicv_inhibit(), as vCPU creation happens before the vCPU is fully onlined, i.e. it won't get the request made to "all" vCPUs. If APICv is globally inhibited between setting apicv_active and onlining the vCPU, the vCPU will end up running with APICv enabled and trigger KVM's sanity check. Mark APICv as active during vCPU creation if APICv is enabled at the module level, both to be optimistic about it's final state, e.g. to avoid additional VMWRITEs on VMX, and because there are likely bugs lurking since KVM checks apicv_active in multiple vCPU creation paths. While keeping the current behavior of consuming kvm_apicv_activated() is arguably safer from a regression perspective, force apicv_active so that vCPU creation runs with deterministic state and so that if there are bugs, they are found sooner than later, i.e. not when some crazy race condition is hit. WARNING: CPU: 0 PID: 484 at arch/x86/kvm/x86.c:9877 vcpu_enter_guest+0x2ae3/0x3ee0 arch/x86/kvm/x86.c:9877 Modules linked in: CPU: 0 PID: 484 Comm: syz-executor361 Not tainted 5.16.13 #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1~cloud0 04/01/2014 RIP: 0010:vcpu_enter_guest+0x2ae3/0x3ee0 arch/x86/kvm/x86.c:9877 Call Trace: <TASK> vcpu_run arch/x86/kvm/x86.c:10039 [inline] kvm_arch_vcpu_ioctl_run+0x337/0x15e0 arch/x86/kvm/x86.c:10234 kvm_vcpu_ioctl+0x4d2/0xc80 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3727 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:874 [inline] __se_sys_ioctl fs/ioctl.c:860 [inline] __x64_sys_ioctl+0x16d/0x1d0 fs/ioctl.c:860 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae The bug was hit by a syzkaller spamming VM creation with 2 vCPUs and a call to KVM_SET_GUEST_DEBUG. r0 = openat$kvm(0xffffffffffffff9c, &(0x7f0000000000), 0x0, 0x0) r1 = ioctl$KVM_CREATE_VM(r0, 0xae01, 0x0) ioctl$KVM_CAP_SPLIT_IRQCHIP(r1, 0x4068aea3, &(0x7f0000000000)) (async) r2 = ioctl$KVM_CREATE_VCPU(r1, 0xae41, 0x0) (async) r3 = ioctl$KVM_CREATE_VCPU(r1, 0xae41, 0x400000000000002) ioctl$KVM_SET_GUEST_DEBUG(r3, 0x4048ae9b, &(0x7f00000000c0)={0x5dda9c14aa95f5c5}) ioctl$KVM_RUN(r2, 0xae80, 0x0) Reported-by: Gaoning Pan <pgn@zju.edu.cn> Reported-by: Yongkang Jia <kangel@zju.edu.cn> Fixes: 8df14af42f00 ("kvm: x86: Add support for dynamic APICv activation") Cc: stable@vger.kernel.org Cc: Maxim Levitsky <mlevitsk@redhat.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> Message-Id: <20220420013732.3308816-4-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.