Commit dd3035a2 authored by Anton Ivanov's avatar Anton Ivanov Committed by Richard Weinberger
Browse files

um: add a UML specific futex implementation 



The generic asm futex implementation emulates atomic access to
memory by doing a get_user followed by put_user. These translate
to two mapping operations on UML with paging enabled in the
meantime. This, in turn may end up changing interrupts,
invoking the signal loop, etc.

This replaces the generic implementation by a mapping followed
by an operation on the mapped segment.

Signed-off-by: default avatarAnton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: default avatarRichard Weinberger <richard@nod.at>
parent c0ecca66

arch/um/include/asm/Kbuild

+0 −1
Original line number Diff line number Diff line
@@ -9,7 +9,6 @@ generic-y += exec.h 
generic-y += extable.h

generic-y += fb.h

generic-y += ftrace.h

generic-y += futex.h

generic-y += hw_irq.h

generic-y += irq_regs.h

generic-y += irq_work.h

arch/um/include/asm/futex.h

0 → 100644
+14 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

#ifndef _ASM_UM_FUTEX_H

#define _ASM_UM_FUTEX_H



#include <linux/futex.h>

#include <linux/uaccess.h>

#include <asm/errno.h>





int arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr);

int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,

			      u32 oldval, u32 newval);



#endif

arch/um/kernel/skas/uaccess.c

+136 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
#include <asm/current.h>

#include <asm/page.h>

#include <kern_util.h>

#include <asm/futex.h>

#include <os.h>



pte_t *virt_to_pte(struct mm_struct *mm, unsigned long addr)
@@ -248,3 +249,138 @@ long __strnlen_user(const void __user *str, long len) 
	return 0;

}

EXPORT_SYMBOL(__strnlen_user);



/**

 * arch_futex_atomic_op_inuser() - Atomic arithmetic operation with constant

 *			  argument and comparison of the previous

 *			  futex value with another constant.

 *

 * @encoded_op:	encoded operation to execute

 * @uaddr:	pointer to user space address

 *

 * Return:

 * 0 - On success

 * -EFAULT - User access resulted in a page fault

 * -EAGAIN - Atomic operation was unable to complete due to contention

 * -ENOSYS - Operation not supported

 */



int arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)

{

	int oldval, ret;

	struct page *page;

	unsigned long addr = (unsigned long) uaddr;

	pte_t *pte;



	ret = -EFAULT;

	if (!access_ok(uaddr, sizeof(*uaddr)))

		return -EFAULT;

	preempt_disable();

	pte = maybe_map(addr, 1);

	if (pte == NULL)

		goto out_inuser;



	page = pte_page(*pte);

#ifdef CONFIG_64BIT

	pagefault_disable();

	addr = (unsigned long) page_address(page) +

			(((unsigned long) addr) & ~PAGE_MASK);

#else

	addr = (unsigned long) kmap_atomic(page) +

		((unsigned long) addr & ~PAGE_MASK);

#endif

	uaddr = (u32 *) addr;

	oldval = *uaddr;



	ret = 0;



	switch (op) {

	case FUTEX_OP_SET:

		*uaddr = oparg;

		break;

	case FUTEX_OP_ADD:

		*uaddr += oparg;

		break;

	case FUTEX_OP_OR:

		*uaddr |= oparg;

		break;

	case FUTEX_OP_ANDN:

		*uaddr &= ~oparg;

		break;

	case FUTEX_OP_XOR:

		*uaddr ^= oparg;

		break;

	default:

		ret = -ENOSYS;

	}

#ifdef CONFIG_64BIT

	pagefault_enable();

#else

	kunmap_atomic((void *)addr);

#endif



out_inuser:

	preempt_enable();



	if (ret == 0)

		*oval = oldval;



	return ret;

}

EXPORT_SYMBOL(arch_futex_atomic_op_inuser);



/**

 * futex_atomic_cmpxchg_inatomic() - Compare and exchange the content of the

 *				uaddr with newval if the current value is

 *				oldval.

 * @uval:	pointer to store content of @uaddr

 * @uaddr:	pointer to user space address

 * @oldval:	old value

 * @newval:	new value to store to @uaddr

 *

 * Return:

 * 0 - On success

 * -EFAULT - User access resulted in a page fault

 * -EAGAIN - Atomic operation was unable to complete due to contention

 * -ENOSYS - Function not implemented (only if !HAVE_FUTEX_CMPXCHG)

 */



int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,

			      u32 oldval, u32 newval)

{

	struct page *page;

	pte_t *pte;

	int ret = -EFAULT;



	if (!access_ok(uaddr, sizeof(*uaddr)))

		return -EFAULT;



	preempt_disable();

	pte = maybe_map((unsigned long) uaddr, 1);

	if (pte == NULL)

		goto out_inatomic;



	page = pte_page(*pte);

#ifdef CONFIG_64BIT

	pagefault_disable();

	uaddr = page_address(page) + (((unsigned long) uaddr) & ~PAGE_MASK);

#else

	uaddr = kmap_atomic(page) + ((unsigned long) uaddr & ~PAGE_MASK);

#endif



	*uval = *uaddr;



	ret = cmpxchg(uaddr, oldval, newval);



#ifdef CONFIG_64BIT

	pagefault_enable();

#else

	kunmap_atomic(uaddr);

#endif

	ret = 0;



out_inatomic:

	preempt_enable();

	return ret;

}

EXPORT_SYMBOL(futex_atomic_cmpxchg_inatomic);