On Thu, Jan 21, 2016 at 4:05 PM, Bryan O'Donoghue <pure.logic@xxxxxxxxxxxxxxxxx> wrote: > Currently when setting up an IMR around the kernel .text area we lock that > IMR, preventing further modification. While superficially this appears to > be the right thing to do, in fact this doesn't account for a legitimate > change in the memory map such as when running through kexec. In such a > scenario a second kernel can have a different size and location to it's > predecessor and can view some of the memory occupied by its predecessor as > legitimately usable RAM. This RAM can then be allocated to DMA agents > within the system and trigger an IMR violation. > > The solution to this situation is to keep the kernel .text section IMR lock > bit false. This means that a subsequent kernel will boot and can tear-down > an existing IMR, while still setting up an IMR around its own .text > section. > Like I said you privately it would be nice to have a knob how to behave. My idea is to provide kernel command line imr= and supply imr=lock when user wants to boot kernel locked. Optionally: add a warning if imr=lock and kernel build with kexec that might bring issues Optionally: add a kernel config option to boot always in locked mode (should depend on !KEXEC) > Signed-off-by: Bryan O'Donoghue <pure.logic@xxxxxxxxxxxxxxxxx> > Reported-by: Andriy Shevchenko <andriy.shevchenko@xxxxxxxxx> > --- > arch/x86/platform/intel-quark/imr.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/platform/intel-quark/imr.c b/arch/x86/platform/intel-quark/imr.c > index c1bdafa..1c43639 100644 > --- a/arch/x86/platform/intel-quark/imr.c > +++ b/arch/x86/platform/intel-quark/imr.c > @@ -591,7 +591,7 @@ static void __init imr_fixup_memmap(struct imr_device *idev) > * from the beginning of the .text secton to the end of the > * .rodata section as one physically contiguous block. > */ > - ret = imr_add_range(base, size, IMR_CPU, IMR_CPU, true); > + ret = imr_add_range(base, size, IMR_CPU, IMR_CPU, false); > if (ret < 0) { > pr_err("unable to setup IMR for kernel: (%p - %p)\n", > &_text, &__end_rodata); > -- > 2.5.0 > -- With Best Regards, Andy Shevchenko -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html