entry: Provide infrastructure for work before transitioning to guest mode

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.

Thomas Gleixner committed 6 years ago

Commit 935ace21 parent a5497ba5 files · +144 −1Browse files

Unified · Split

5 files

include/linux/entry-kvm.h +80 −0
include/linux/kvm_host.h +8 −0
kernel/entry/Makefile +2 −1
kernel/entry/kvm.c +51 −0
virt/kvm/Kconfig +3 −0

include/linux/entry-kvm.h+80−0

@@ -0,0 +1,80 @@
	1	/* SPDX-License-Identifier: GPL-2.0 */
	2	#ifndef __LINUX_ENTRYKVM_H
	3	#define __LINUX_ENTRYKVM_H
	4
	5	#include <linux/entry-common.h>
	6
	7	/* Transfer to guest mode work */
	8	#ifdef CONFIG_KVM_XFER_TO_GUEST_WORK
	9
	10	#ifndef ARCH_XFER_TO_GUEST_MODE_WORK
	11	# define ARCH_XFER_TO_GUEST_MODE_WORK (0)
	12	#endif
	13
	14	#define XFER_TO_GUEST_MODE_WORK \
	15	(_TIF_NEED_RESCHED \| _TIF_SIGPENDING \| \
	16	_TIF_NOTIFY_RESUME \| ARCH_XFER_TO_GUEST_MODE_WORK)
	17
	18	struct kvm_vcpu;
	19
	20	/**
	21	* arch_xfer_to_guest_mode_handle_work - Architecture specific xfer to guest
	22	* mode work handling function.
	23	* @vcpu: Pointer to current's VCPU data
	24	* @ti_work: Cached TIF flags gathered in xfer_to_guest_mode_handle_work()
	25	*
	26	* Invoked from xfer_to_guest_mode_handle_work(). Defaults to NOOP. Can be
	27	* replaced by architecture specific code.
	28	*/
	29	static inline int arch_xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu,
	30	unsigned long ti_work);
	31
	32	#ifndef arch_xfer_to_guest_mode_work
	33	static inline int arch_xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu,
	34	unsigned long ti_work)
	35	{
	36	return 0;
	37	}
	38	#endif
	39
	40	/**
	41	* xfer_to_guest_mode_handle_work - Check and handle pending work which needs
	42	* to be handled before going to guest mode
	43	* @vcpu: Pointer to current's VCPU data
	44	*
	45	* Returns: 0 or an error code
	46	*/
	47	int xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu);
	48
	49	/**
	50	* __xfer_to_guest_mode_work_pending - Check if work is pending
	51	*
	52	* Returns: True if work pending, False otherwise.
	53	*
	54	* Bare variant of xfer_to_guest_mode_work_pending(). Can be called from
	55	* interrupt enabled code for racy quick checks with care.
	56	*/
	57	static inline bool __xfer_to_guest_mode_work_pending(void)
	58	{
	59	unsigned long ti_work = READ_ONCE(current_thread_info()->flags);
	60
	61	return !!(ti_work & XFER_TO_GUEST_MODE_WORK);
	62	}
	63
	64	/**
	65	* xfer_to_guest_mode_work_pending - Check if work is pending which needs to be
	66	* handled before returning to guest mode
	67	*
	68	* Returns: True if work pending, False otherwise.
	69	*
	70	* Has to be invoked with interrupts disabled before the transition to
	71	* guest mode.
	72	*/
	73	static inline bool xfer_to_guest_mode_work_pending(void)
	74	{
	75	lockdep_assert_irqs_disabled();
	76	return __xfer_to_guest_mode_work_pending();
	77	}
	78	#endif /* CONFIG_KVM_XFER_TO_GUEST_WORK */
	79
	80	#endif

include/linux/kvm_host.h+8−0

@@ -1439,4 +1439,12 @@ int kvm_vm_create_worker_thread(struct kvm *kvm, kvm_vm_thread_fn_t thread_fn, · 1438 unmodified lines
1439	uintptr_t data, const char *name,	1439	uintptr_t data, const char *name,
1440	struct task_struct **thread_ptr);	1440	struct task_struct **thread_ptr);
1441		1441
		1442	#ifdef CONFIG_KVM_XFER_TO_GUEST_WORK
		1443	static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
		1444	{
		1445	vcpu->run->exit_reason = KVM_EXIT_INTR;
		1446	vcpu->stat.signal_exits++;
		1447	}
		1448	#endif /* CONFIG_KVM_XFER_TO_GUEST_WORK */
		1449
1442	#endif	1450	#endif

kernel/entry/Makefile+2−1

@@ -9,4 +9,5 @@ KCOV_INSTRUMENT := n · 8 unmodified lines
9	CFLAGS_REMOVE_common.o = -fstack-protector -fstack-protector-strong	9	CFLAGS_REMOVE_common.o = -fstack-protector -fstack-protector-strong
10	CFLAGS_common.o += -fno-stack-protector	10	CFLAGS_common.o += -fno-stack-protector
11		11
12	obj-$(CONFIG_GENERIC_ENTRY) += common.o	12	obj-$(CONFIG_GENERIC_ENTRY) += common.o
		13	obj-$(CONFIG_KVM_XFER_TO_GUEST_WORK) += kvm.o

kernel/entry/kvm.c+51−0

@@ -0,0 +1,51 @@
	1	// SPDX-License-Identifier: GPL-2.0
	2
	3	#include <linux/entry-kvm.h>
	4	#include <linux/kvm_host.h>
	5
	6	static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
	7	{
	8	do {
	9	int ret;
	10
	11	if (ti_work & _TIF_SIGPENDING) {
	12	kvm_handle_signal_exit(vcpu);
	13	return -EINTR;
	14	}
	15
	16	if (ti_work & _TIF_NEED_RESCHED)
	17	schedule();
	18
	19	if (ti_work & _TIF_NOTIFY_RESUME) {
	20	clear_thread_flag(TIF_NOTIFY_RESUME);
	21	tracehook_notify_resume(NULL);
	22	}
	23
	24	ret = arch_xfer_to_guest_mode_handle_work(vcpu, ti_work);
	25	if (ret)
	26	return ret;
	27
	28	ti_work = READ_ONCE(current_thread_info()->flags);
	29	} while (ti_work & XFER_TO_GUEST_MODE_WORK \|\| need_resched());
	30	return 0;
	31	}
	32
	33	int xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu)
	34	{
	35	unsigned long ti_work;
	36
	37	/*
	38	* This is invoked from the outer guest loop with interrupts and
	39	* preemption enabled.
	40	*
	41	* KVM invokes xfer_to_guest_mode_work_pending() with interrupts
	42	* disabled in the inner loop before going into guest mode. No need
	43	* to disable interrupts here.
	44	*/
	45	ti_work = READ_ONCE(current_thread_info()->flags);
	46	if (!(ti_work & XFER_TO_GUEST_MODE_WORK))
	47	return 0;
	48
	49	return xfer_to_guest_mode_work(vcpu, ti_work);
	50	}
	51	EXPORT_SYMBOL_GPL(xfer_to_guest_mode_handle_work);

virt/kvm/Kconfig+3−0

@@ -60,3 +60,6 @@ config HAVE_KVM_VCPU_RUN_PID_CHANGE · 59 unmodified lines
60		60
61	config HAVE_KVM_NO_POLL	61	config HAVE_KVM_NO_POLL
62	bool	62	bool
		63
		64	config KVM_XFER_TO_GUEST_WORK
		65	bool