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6a65d26385
Guests running within virtual machines might be affected by SMP effects even if the guest itself is compiled without SMP support. This is an artifact of interfacing with an SMP host while running an UP kernel. Using mandatory barriers for this use-case would be possible but is often suboptimal. In particular, virtio uses a bunch of confusing ifdefs to work around this, while xen just uses the mandatory barriers. To better handle this case, low-level virt_mb() etc macros are made available. These are implemented trivially using the low-level __smp_xxx macros, the purpose of these wrappers is to annotate those specific cases. These have the same effect as smp_mb() etc when SMP is enabled, but generate identical code for SMP and non-SMP systems. For example, virtual machine guests should use virt_mb() rather than smp_mb() when synchronizing against a (possibly SMP) host. Suggested-by: David Miller <davem@davemloft.net> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
212 lines
4.4 KiB
C
212 lines
4.4 KiB
C
/*
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* Generic barrier definitions, originally based on MN10300 definitions.
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*
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* It should be possible to use these on really simple architectures,
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* but it serves more as a starting point for new ports.
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*
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* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#ifndef __ASM_GENERIC_BARRIER_H
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#define __ASM_GENERIC_BARRIER_H
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#ifndef __ASSEMBLY__
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#include <linux/compiler.h>
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#ifndef nop
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#define nop() asm volatile ("nop")
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#endif
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/*
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* Force strict CPU ordering. And yes, this is required on UP too when we're
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* talking to devices.
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*
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* Fall back to compiler barriers if nothing better is provided.
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*/
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#ifndef mb
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#define mb() barrier()
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#endif
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#ifndef rmb
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#define rmb() mb()
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#endif
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#ifndef wmb
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#define wmb() mb()
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#endif
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#ifndef dma_rmb
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#define dma_rmb() rmb()
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#endif
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#ifndef dma_wmb
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#define dma_wmb() wmb()
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#endif
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#ifndef read_barrier_depends
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#define read_barrier_depends() do { } while (0)
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#endif
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#ifndef __smp_mb
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#define __smp_mb() mb()
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#endif
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#ifndef __smp_rmb
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#define __smp_rmb() rmb()
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#endif
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#ifndef __smp_wmb
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#define __smp_wmb() wmb()
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#endif
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#ifndef __smp_read_barrier_depends
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#define __smp_read_barrier_depends() read_barrier_depends()
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#endif
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#ifdef CONFIG_SMP
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#ifndef smp_mb
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#define smp_mb() __smp_mb()
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#endif
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#ifndef smp_rmb
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#define smp_rmb() __smp_rmb()
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#endif
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#ifndef smp_wmb
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#define smp_wmb() __smp_wmb()
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#endif
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#ifndef smp_read_barrier_depends
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#define smp_read_barrier_depends() __smp_read_barrier_depends()
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#endif
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#else /* !CONFIG_SMP */
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#ifndef smp_mb
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#define smp_mb() barrier()
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#endif
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#ifndef smp_rmb
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#define smp_rmb() barrier()
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#endif
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#ifndef smp_wmb
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#define smp_wmb() barrier()
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#endif
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#ifndef smp_read_barrier_depends
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#define smp_read_barrier_depends() do { } while (0)
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#endif
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#endif /* CONFIG_SMP */
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#ifndef __smp_store_mb
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#define __smp_store_mb(var, value) do { WRITE_ONCE(var, value); __smp_mb(); } while (0)
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#endif
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#ifndef __smp_mb__before_atomic
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#define __smp_mb__before_atomic() __smp_mb()
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#endif
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#ifndef __smp_mb__after_atomic
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#define __smp_mb__after_atomic() __smp_mb()
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#endif
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#ifndef __smp_store_release
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#define __smp_store_release(p, v) \
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do { \
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compiletime_assert_atomic_type(*p); \
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__smp_mb(); \
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WRITE_ONCE(*p, v); \
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} while (0)
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#endif
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#ifndef __smp_load_acquire
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#define __smp_load_acquire(p) \
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({ \
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typeof(*p) ___p1 = READ_ONCE(*p); \
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compiletime_assert_atomic_type(*p); \
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__smp_mb(); \
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___p1; \
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})
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#endif
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#ifdef CONFIG_SMP
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#ifndef smp_store_mb
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#define smp_store_mb(var, value) __smp_store_mb(var, value)
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#endif
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#ifndef smp_mb__before_atomic
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#define smp_mb__before_atomic() __smp_mb__before_atomic()
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#endif
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#ifndef smp_mb__after_atomic
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#define smp_mb__after_atomic() __smp_mb__after_atomic()
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#endif
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#ifndef smp_store_release
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#define smp_store_release(p, v) __smp_store_release(p, v)
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#endif
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#ifndef smp_load_acquire
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#define smp_load_acquire(p) __smp_load_acquire(p)
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#endif
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#else /* !CONFIG_SMP */
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#ifndef smp_store_mb
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#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0)
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#endif
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#ifndef smp_mb__before_atomic
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#define smp_mb__before_atomic() barrier()
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#endif
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#ifndef smp_mb__after_atomic
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#define smp_mb__after_atomic() barrier()
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#endif
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#ifndef smp_store_release
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#define smp_store_release(p, v) \
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do { \
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compiletime_assert_atomic_type(*p); \
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barrier(); \
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WRITE_ONCE(*p, v); \
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} while (0)
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#endif
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#ifndef smp_load_acquire
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#define smp_load_acquire(p) \
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({ \
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typeof(*p) ___p1 = READ_ONCE(*p); \
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compiletime_assert_atomic_type(*p); \
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barrier(); \
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___p1; \
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})
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#endif
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#endif
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/* Barriers for virtual machine guests when talking to an SMP host */
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#define virt_mb() __smp_mb()
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#define virt_rmb() __smp_rmb()
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#define virt_wmb() __smp_wmb()
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#define virt_read_barrier_depends() __smp_read_barrier_depends()
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#define virt_store_mb(var, value) __smp_store_mb(var, value)
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#define virt_mb__before_atomic() __smp_mb__before_atomic()
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#define virt_mb__after_atomic() __smp_mb__after_atomic()
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#define virt_store_release(p, v) __smp_store_release(p, v)
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#define virt_load_acquire(p) __smp_load_acquire(p)
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#endif /* !__ASSEMBLY__ */
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#endif /* __ASM_GENERIC_BARRIER_H */
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