>There seems to be support for block stepping in arch/x86/kernel/step.c, >which is used by kernel/ptrace.c. > >This is now another user for the DEBUGCTL MSR; the access needs to be >synchronized. I'll look into it.
I looked into the new block/single stepping support in arch/x86/kernel/step.c. It uses a TIF DEBUGCTLMSR and a field unsigned long debugctlmsr in struct thread_struct. When they are done stepping, they clear the TIF and the MSR. Our patch uses a ds_area field in struct thread_struct and two TIF to mark the functionality, rather than the resource. We need to access the DEBUGCTL and DS_SAVE_AREA MSR's. I would rewrite our patch to rename the TIF to name the used resource and move the code setting the DS_SAVE_AREA MSR to __switch_to_xtra; that leaves only the code to take the timestamp in ptrace_bts.c. The two MSR accesses (or, rather, the two users of the TIF) still conflict. When either is done, he clears the TIF bit and thus disables the other user. I would introduce a convention: - each user clears only the debugctl bits he used - the TIF bit is cleared, if thread_struct.debugctlmsr == 0 - before setting any bit, each user first checks all bits he intends to set if any is set already, he bails out with an error Is there some better way to do this? thanks and regards, markus. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/