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Revision 32ffa4f71e10009498ae6b54da65ab316db967bd authored by Axel Rasmussen on 19 May 2021, 20:03:33 UTC, committed by Paolo Bonzini on 27 May 2021, 11:45:55 UTC 
KVM: selftests: compute correct demand paging size
 
This is a preparatory commit needed before we can use different kinds of
backing pages for guest memory.

Previously, we used perf_test_args.host_page_size, which is the host's
native page size (commonly 4K). For VM_MEM_SRC_ANONYMOUS this turns out
to be okay, but in a follow-up commit we want to allow using different
kinds of backing memory.

Take VM_MEM_SRC_ANONYMOUS_HUGETLB for example. Without this change, if
we used that backing page type, when we issued a UFFDIO_COPY ioctl we'd
only do so with 4K, rather than the full 2M of a backing hugepage. In
this case, UFFDIO_COPY returns -EINVAL (__mcopy_atomic_hugetlb checks
the size).

Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Message-Id: <20210519200339.829146-5-axelrasmussen@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 parent 25408e5
Raw File
is_single_threaded.c 
// SPDX-License-Identifier: GPL-2.0-or-later
/* Function to determine if a thread group is single threaded or not
 *
 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 * - Derived from security/selinux/hooks.c
 */
#include <linux/sched/signal.h>
#include <linux/sched/task.h>
#include <linux/sched/mm.h>

/*
 * Returns true if the task does not share ->mm with another thread/process.
 */
bool current_is_single_threaded(void)
{
	struct task_struct *task = current;
	struct mm_struct *mm = task->mm;
	struct task_struct *p, *t;
	bool ret;

	if (atomic_read(&task->signal->live) != 1)
		return false;

	if (atomic_read(&mm->mm_users) == 1)
		return true;

	ret = false;
	rcu_read_lock();
	for_each_process(p) {
		if (unlikely(p->flags & PF_KTHREAD))
			continue;
		if (unlikely(p == task->group_leader))
			continue;

		for_each_thread(p, t) {
			if (unlikely(t->mm == mm))
				goto found;
			if (likely(t->mm))
				break;
			/*
			 * t->mm == NULL. Make sure next_thread/next_task
			 * will see other CLONE_VM tasks which might be
			 * forked before exiting.
			 */
			smp_rmb();
		}
	}
	ret = true;
found:
	rcu_read_unlock();

	return ret;
}
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