On Fri, Jul 6, 2012 at 11:16 AM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > If some code then changes the values in the pt_regs, it is *that* code > that needs to think twice about what it does. Where is that code? >From a quick grep it looks like it is __intel_pmu_pebs_event() that does this. THAT is where you would possibly have a huge honking big comment about how you have to fake the CS register contents because the PEBS information is incomplete. But make it clear that it is a total hack. Also, somebody should check. Is the PEBS information *actually* the instruction pointer (address within the code segment), or is it the "linear address" (segment base + rip)? I hope it is the latter, because in the absense of CS, the segment-based address is very unclear indeed. And if it *is* the linear address, then at that point you could do regs->cs = kernel_ip(ip) ? __KERNEL_CS : __USER_CS; regs->eflags &= ~X86_EFLAGS_VM; and document this as a "we fake the CS and vm86 mode, using the known zero-based code segments". At that point it would be technically correct. But any code that does "kernel_ip(regs->ip)" is just terminally confused and can never be sane. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html