• Peter Zijlstra's avatar
    perf/x86: Fix USER/KERNEL tagging of samples properly · d07bdfd3
    Peter Zijlstra authored
    Some PMUs don't provide a full register set for their sample,
    specifically 'advanced' PMUs like AMD IBS and Intel PEBS which provide
    'better' than regular interrupt accuracy.
    
    In this case we use the interrupt regs as basis and over-write some
    fields (typically IP) with different information.
    
    The perf core however uses user_mode() to distinguish user/kernel
    samples, user_mode() relies on regs->cs. If the interrupt skid pushed
    us over a boundary the new IP might not be in the same domain as the
    interrupt.
    
    Commit ce5c1fe9 ("perf/x86: Fix USER/KERNEL tagging of samples")
    tried to fix this by making the perf core use kernel_ip(). This
    however is wrong (TM), as pointed out by Linus, since it doesn't allow
    for VM86 and non-zero based segments in IA32 mode.
    
    Therefore, provide a new helper to set the regs->ip field,
    set_linear_ip(), which massages the regs into a suitable state
    assuming the provided IP is in fact a linear address.
    
    Also modify perf_instruction_pointer() and perf_callchain_user() to
    deal with segments base offsets.
    Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/1341910954.3462.102.camel@twinsSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    d07bdfd3
perf_event.h 15.5 KB