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authorRob Gardner <rob.gardner@oracle.com>2017-07-17 09:22:27 -0600
committerDavid S. Miller <davem@davemloft.net>2017-07-18 11:25:52 -0700
commitfc290a114fc6034b0f6a5a46e2fb7d54976cf87a (patch)
treee85cf28ba65067495ce49e02bd4387830cb50c1e /arch/sparc/configs
parentMerge git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc (diff)
downloadlinux-dev-fc290a114fc6034b0f6a5a46e2fb7d54976cf87a.tar.xz
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sparc64: Prevent perf from running during super critical sections
This fixes another cause of random segfaults and bus errors that may occur while running perf with the callgraph option. Critical sections beginning with spin_lock_irqsave() raise the interrupt level to PIL_NORMAL_MAX (14) and intentionally do not block performance counter interrupts, which arrive at PIL_NMI (15). But some sections of code are "super critical" with respect to perf because the perf_callchain_user() path accesses user space and may cause TLB activity as well as faults as it unwinds the user stack. One particular critical section occurs in switch_mm: spin_lock_irqsave(&mm->context.lock, flags); ... load_secondary_context(mm); tsb_context_switch(mm); ... spin_unlock_irqrestore(&mm->context.lock, flags); If a perf interrupt arrives in between load_secondary_context() and tsb_context_switch(), then perf_callchain_user() could execute with the context ID of one process, but with an active TSB for a different process. When the user stack is accessed, it is very likely to incur a TLB miss, since the h/w context ID has been changed. The TLB will then be reloaded with a translation from the TSB for one process, but using a context ID for another process. This exposes memory from one process to another, and since it is a mapping for stack memory, this usually causes the new process to crash quickly. This super critical section needs more protection than is provided by spin_lock_irqsave() since perf interrupts must not be allowed in. Since __tsb_context_switch already goes through the trouble of disabling interrupts completely, we fix this by moving the secondary context load down into this better protected region. Orabug: 25577560 Signed-off-by: Dave Aldridge <david.j.aldridge@oracle.com> Signed-off-by: Rob Gardner <rob.gardner@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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