Benjamin Herrenschmidt <b...@kernel.crashing.org> wrote on 2012/06/01 11:12:51: > > On Thu, 2012-05-31 at 11:05 +0200, Joakim Tjernlund wrote: > > Abatron Support <supp...@abatron.ch> wrote on 2012/05/30 14:08:26: > > > > > > >> I have tested this briefly with BDI2000 on P2010(e500) and > > > >> it works for me. I don't know if there are any bad side effects, > > > >> therfore > > > >> this RFC. > > > > > > > We used to have MSR_DE surrounded by CONFIG_something > > > > to ensure it wasn't set under normal operation. IIRC, if MSR_DE > > > > is set, you will have problems with software debuggers that > > > > utilize the the debugging registers in the chip itself. You only want > > > > to force this to be set when using the BDI, not at other times. > > > > > > This MSR_DE is also of interest and used for software debuggers that > > > make use of the debug registers. Only if MSR_DE is set then debug > > > interrupts are generated. If a debug event leads to a debug interrupt > > > handled by a software debugger or if it leads to a debug halt handled > > > by a JTAG tool is selected with DBCR0_EDM / DBCR0_IDM. > > > > > > The "e500 Core Family Reference Manual" chapter "Chapter 8 > > > Debug Support" explains in detail the effect of MSR_DE. > > > > So what is the verdict on this? I don't buy into Dan argument without some > > hard data. > > The kernel normally controls when to set or not set MSR:DE, at least > when using SW breakpoints. Setting it globally should remain some kind > of specific debug option. > > In fact on some CPUs, we even leave user set dbcr settings and rely on > DE being off in kernel space to avoid user->kernel attacks via the debug > registers (I think we still do that on 64-bit BookE though it should > eventually change).
hmm, would it not be better to always clear out/control dbcr settings and always have MSR:DE on? It would be much easier to control dbcr, even dynamically, than MSR:DE Jocke _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev