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e3c1d51868
commita493d1ca1aupstream. sync_core_before_usermode() had an incorrect optimization. If the kernel returns from an interrupt, it can get to usermode without IRET. It just has to schedule to a different task in the same mm and do SYSRET. Fortunately, there were no callers of sync_core_before_usermode() that could have had in_irq() or in_nmi() equal to true, because it's only ever called from the scheduler. While at it, clarify a related comment. Fixes:70216e18e5("membarrier: Provide core serializing command, *_SYNC_CORE") Signed-off-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/5afc7632be1422f91eaf7611aaaa1b5b8580a086.1607058304.git.luto@kernel.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
29 lines
894 B
C
29 lines
894 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_SYNC_CORE_H
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#define _ASM_X86_SYNC_CORE_H
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#include <linux/preempt.h>
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#include <asm/processor.h>
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#include <asm/cpufeature.h>
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/*
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* Ensure that a core serializing instruction is issued before returning
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* to user-mode. x86 implements return to user-space through sysexit,
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* sysrel, and sysretq, which are not core serializing.
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*/
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static inline void sync_core_before_usermode(void)
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{
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/* With PTI, we unconditionally serialize before running user code. */
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if (static_cpu_has(X86_FEATURE_PTI))
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return;
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/*
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* Even if we're in an interrupt, we might reschedule before returning,
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* in which case we could switch to a different thread in the same mm
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* and return using SYSRET or SYSEXIT. Instead of trying to keep
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* track of our need to sync the core, just sync right away.
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*/
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sync_core();
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}
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#endif /* _ASM_X86_SYNC_CORE_H */
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