On Wed, Jul 22, 2020 at 11:59:59PM +0200, Thomas Gleixner wrote: > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > Entering a guest is similar to exiting to user space. Pending work like > handling signals, rescheduling, task work etc. needs to be handled before > that. > > Provide generic infrastructure to avoid duplication of the same handling > code all over the place. > > The transfer to guest mode handling is different from the exit to usermode > handling, e.g. vs. rseq and live patching, so a separate function is used. > > The initial list of work items handled is: > > TIF_SIGPENDING, TIF_NEED_RESCHED, TIF_NOTIFY_RESUME > > Architecture specific TIF flags can be added via defines in the > architecture specific include files. > > The calling convention is also different from the syscall/interrupt entry > functions as KVM invokes this from the outer vcpu_run() loop with > interrupts and preemption enabled. To prevent missing a pending work item > it invokes a check for pending TIF work from interrupt disabled code right > before transitioning to guest mode. The lockdep, RCU and tracing state > handling is also done directly around the switch to and from guest mode. > > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> SR-IOV will start trigger a warning below in this commit, A reproducer: # echo 1 > /sys/class/net/eno58/device/sriov_numvfs (bnx2x) # git clone https://gitlab.com/cailca/linux-mm # cd linux-mm; make # ./random -x 0-100 -k0000:02:09.0 https://gitlab.com/cailca/linux-mm/-/blob/master/random.c#L1247 (x86.config is also included in the repo.) [ 765.409027] ------------[ cut here ]------------ [ 765.434611] WARNING: CPU: 13 PID: 3377 at include/linux/entry-kvm.h:75 kvm_arch_vcpu_ioctl_run+0xb52/0x1320 [kvm] [ 765.487229] Modules linked in: vfio_pci vfio_virqfd vfio_iommu_type1 vfio loop nls_ascii nls_cp437 vfat fat [ 766.118568] CPU: 13 PID: 3377 Comm: qemu-kvm Not tainted 5.8.0-rc7-next-20200729 #2 [ 766.147011] ? kthread_create_worker_on_cpu+0xc0/0xc0 [ 766.147016] ret_from_fork+0x22/0x30 [ 766.782999] Hardware name: HP ProLiant BL660c Gen9, BIOS I38 10/17/2018 [ 766.817799] RIP: 0010:kvm_arch_vcpu_ioctl_run+0xb52/0x1320 [kvm] [ 766.850054] Code: e8 03 0f b6 04 18 84 c0 74 06 0f 8e 4a 03 00 00 41 c6 85 50 2d 00 00 00 e9 24 f8 ff ff 4c 89 ef e8 93 a8 02 00 e9 3d f8 ff ff <0f> 0b e9 f2 f8 ff ff 48 81 c6 c0 01 00 00 4c 89 ef e8 18 4c fe ff [ 766.942485] RSP: 0018:ffffc90007017b58 EFLAGS: 00010202 [ 766.970899] RAX: 0000000000000001 RBX: dffffc0000000000 RCX: ffffffffc0f0ef8a [ 767.008488] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff88956a3821a0 [ 767.045726] RBP: ffffc90007017bb8 R08: ffffed1269290010 R09: ffffed1269290010 [ 767.083242] R10: ffff88934948007f R11: ffffed126929000f R12: ffff889349480424 [ 767.120809] R13: ffff889349480040 R14: ffff88934948006c R15: ffff88980e2da000 [ 767.160531] FS: 00007f12b0e98700(0000) GS:ffff88985fa40000(0000) knlGS:0000000000000000 [ 767.203199] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 767.235083] CR2: 0000000000000000 CR3: 000000120d186002 CR4: 00000000001726e0 [ 767.272303] Call Trace: [ 767.272303] Call Trace: [ 767.286947] kvm_vcpu_ioctl+0x3e9/0xb30 [kvm] [ 767.311162] ? kvm_vcpu_block+0xd30/0xd30 [kvm] [ 767.335281] ? find_held_lock+0x33/0x1c0 [ 767.357492] ? __fget_files+0x1cb/0x300 [ 767.378687] ? lock_downgrade+0x730/0x730 [ 767.401410] ? rcu_read_lock_held+0xaa/0xc0 [ 767.424228] ? rcu_read_lock_sched_held+0xd0/0xd0 [ 767.450078] ? find_held_lock+0x33/0x1c0 [ 767.471876] ? __fget_files+0x1e5/0x300 [ 767.493841] __x64_sys_ioctl+0x315/0x102f [ 767.516579] ? generic_block_fiemap+0x60/0x60 [ 767.540678] ? syscall_enter_from_user_mode+0x1b/0x210 [ 767.568612] ? rcu_read_lock_sched_held+0xaa/0xd0 [ 767.593950] ? lockdep_hardirqs_on_prepare+0x33e/0x4e0 [ 767.621355] ? syscall_enter_from_user_mode+0x20/0x210 [ 767.649283] ? trace_hardirqs_on+0x20/0x1b5 [ 767.673770] do_syscall_64+0x33/0x40 [ 767.694699] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 767.723392] RIP: 0033:0x7f12b999a87b [ 767.744252] Code: 0f 1e fa 48 8b 05 0d 96 2c 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d dd 95 2c 00 f7 d8 64 89 8 [ 767.837418] RSP: 002b:00007f12b0e97678 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [ 767.877074] RAX: ffffffffffffffda RBX: 000055712c857c60 RCX: 00007f12b999a87b [ 767.914242] RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000014 [ 767.951945] RBP: 000055712c857cfb R08: 000055712ac4fad0 R09: 000055712b3f2080 [ 767.989036] R10: 0000000000000000 R11: 0000000000000246 R12: 000055712ac38100 [ 768.025851] R13: 00007ffd996e9edf R14: 00007f12becc5000 R15: 000055712c857c60 [ 768.063363] irq event stamp: 5257 [ 768.082559] hardirqs last enabled at (5273): [<ffffffffa1800ce2>] asm_sysvec_call_function_single+0x12/0x20 [ 768.132704] hardirqs last disabled at (5290): [<ffffffffa179ae3d>] irqentry_enter+0x1d/0x50 [ 768.176563] softirqs last enabled at (5108): [<ffffffffa1a0070f>] __do_softirq+0x70f/0xa9f [ 768.221270] softirqs last disabled at (5093): [<ffffffffa1800ec2>] asm_call_on_stack+0x12/0x20 [ 768.267273] ---[ end trace 8730450ad8cfee9f ]--- > --- > V5: Rename exit -> xfer (Sean) > > V3: Reworked and simplified version adopted to recent X86 and KVM changes > > V2: Moved KVM specific functions to kvm (Paolo) > Added lockdep assert (Andy) > Dropped live patching from enter guest mode work (Miroslav) > --- > include/linux/entry-kvm.h | 80 ++++++++++++++++++++++++++++++++++++++++++++++ > include/linux/kvm_host.h | 8 ++++ > kernel/entry/Makefile | 3 + > kernel/entry/kvm.c | 51 +++++++++++++++++++++++++++++ > virt/kvm/Kconfig | 3 + > 5 files changed, 144 insertions(+), 1 deletion(-) > > --- /dev/null > +++ b/include/linux/entry-kvm.h > @@ -0,0 +1,80 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef __LINUX_ENTRYKVM_H > +#define __LINUX_ENTRYKVM_H > + > +#include <linux/entry-common.h> > + > +/* Transfer to guest mode work */ > +#ifdef CONFIG_KVM_XFER_TO_GUEST_WORK > + > +#ifndef ARCH_XFER_TO_GUEST_MODE_WORK > +# define ARCH_XFER_TO_GUEST_MODE_WORK (0) > +#endif > + > +#define XFER_TO_GUEST_MODE_WORK \ > + (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \ > + _TIF_NOTIFY_RESUME | ARCH_XFER_TO_GUEST_MODE_WORK) > + > +struct kvm_vcpu; > + > +/** > + * arch_xfer_to_guest_mode_work - Architecture specific xfer to guest mode > + * work function. > + * @vcpu: Pointer to current's VCPU data > + * @ti_work: Cached TIF flags gathered in xfer_to_guest_mode() > + * > + * Invoked from xfer_to_guest_mode_work(). Defaults to NOOP. Can be > + * replaced by architecture specific code. > + */ > +static inline int arch_xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, > + unsigned long ti_work); > + > +#ifndef arch_xfer_to_guest_mode_work > +static inline int arch_xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, > + unsigned long ti_work) > +{ > + return 0; > +} > +#endif > + > +/** > + * xfer_to_guest_mode - Check and handle pending work which needs to be > + * handled before returning to guest mode > + * @vcpu: Pointer to current's VCPU data > + * > + * Returns: 0 or an error code > + */ > +int xfer_to_guest_mode(struct kvm_vcpu *vcpu); > + > +/** > + * __xfer_to_guest_mode_work_pending - Check if work is pending > + * > + * Returns: True if work pending, False otherwise. > + * > + * Bare variant of xfer_to_guest_mode_work_pending(). Can be called from > + * interrupt enabled code for racy quick checks with care. > + */ > +static inline bool __xfer_to_guest_mode_work_pending(void) > +{ > + unsigned long ti_work = READ_ONCE(current_thread_info()->flags); > + > + return !!(ti_work & XFER_TO_GUEST_MODE_WORK); > +} > + > +/** > + * xfer_to_guest_mode_work_pending - Check if work is pending which needs to be > + * handled before returning to guest mode > + * > + * Returns: True if work pending, False otherwise. > + * > + * Has to be invoked with interrupts disabled before the transition to > + * guest mode. > + */ > +static inline bool xfer_to_guest_mode_work_pending(void) > +{ > + lockdep_assert_irqs_disabled(); > + return __xfer_to_guest_mode_work_pending(); > +} > +#endif /* CONFIG_KVM_XFER_TO_GUEST_WORK */ > + > +#endif > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -1439,4 +1439,12 @@ int kvm_vm_create_worker_thread(struct k > uintptr_t data, const char *name, > struct task_struct **thread_ptr); > > +#ifdef CONFIG_KVM_XFER_TO_GUEST_WORK > +static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu) > +{ > + vcpu->run->exit_reason = KVM_EXIT_INTR; > + vcpu->stat.signal_exits++; > +} > +#endif /* CONFIG_KVM_XFER_TO_GUEST_WORK */ > + > #endif > --- a/kernel/entry/Makefile > +++ b/kernel/entry/Makefile > @@ -9,4 +9,5 @@ KCOV_INSTRUMENT := n > CFLAGS_REMOVE_common.o = -fstack-protector -fstack-protector-strong > CFLAGS_common.o += -fno-stack-protector > > -obj-$(CONFIG_GENERIC_ENTRY) += common.o > +obj-$(CONFIG_GENERIC_ENTRY) += common.o > +obj-$(CONFIG_KVM_XFER_TO_GUEST_WORK) += kvm.o > --- /dev/null > +++ b/kernel/entry/kvm.c > @@ -0,0 +1,51 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +#include <linux/entry-kvm.h> > +#include <linux/kvm_host.h> > + > +static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work) > +{ > + do { > + int ret; > + > + if (ti_work & _TIF_SIGPENDING) { > + kvm_handle_signal_exit(vcpu); > + return -EINTR; > + } > + > + if (ti_work & _TIF_NEED_RESCHED) > + schedule(); > + > + if (ti_work & _TIF_NOTIFY_RESUME) { > + clear_thread_flag(TIF_NOTIFY_RESUME); > + tracehook_notify_resume(NULL); > + } > + > + ret = arch_xfer_to_guest_mode_work(vcpu, ti_work); > + if (ret) > + return ret; > + > + ti_work = READ_ONCE(current_thread_info()->flags); > + } while (ti_work & XFER_TO_GUEST_MODE_WORK || need_resched()); > + return 0; > +} > + > +int xfer_to_guest_mode(struct kvm_vcpu *vcpu) > +{ > + unsigned long ti_work; > + > + /* > + * This is invoked from the outer guest loop with interrupts and > + * preemption enabled. > + * > + * KVM invokes xfer_to_guest_mode_work_pending() with interrupts > + * disabled in the inner loop before going into guest mode. No need > + * to disable interrupts here. > + */ > + ti_work = READ_ONCE(current_thread_info()->flags); > + if (!(ti_work & XFER_TO_GUEST_MODE_WORK)) > + return 0; > + > + return xfer_to_guest_mode_work(vcpu, ti_work); > +} > +EXPORT_SYMBOL_GPL(xfer_to_guest_mode); > --- a/virt/kvm/Kconfig > +++ b/virt/kvm/Kconfig > @@ -60,3 +60,6 @@ config HAVE_KVM_VCPU_RUN_PID_CHANGE > > config HAVE_KVM_NO_POLL > bool > + > +config KVM_XFER_TO_GUEST_WORK > + bool >
