On Tue, Jul 14, 2009 at 01:12:24PM -0700, David Miller wrote: > From: Joerg Roedel <joerg.roedel@xxxxxxx> > Date: Tue, 14 Jul 2009 11:23:55 +0200 > > > On Tue, Jul 14, 2009 at 10:40:16AM +0900, FUJITA Tomonori wrote: > >> On Mon, 13 Jul 2009 20:56:21 -0400 > >> Robert Reif <reif@xxxxxxxxxxxxx> wrote: > >> > >> > The bad address is within the kernel so it looks like > >> > it's catching a real bug. > >> > > >> > cat kallsyms | grep f0007000 > >> > f0007000 T trapbase_cpu3 > >> > > >> > WARNING: at lib/dma-debug.c:873 check_for_illegal_area+0xc8/0x100() > >> > esp ffd7ba30: DMA-API: device driver maps memory from kernel text or > >> > rodata [addr=f0007000] [len=4096] > >> > Modules linked in: ext3 jbd sd_mod sun_esp esp_scsi scsi_transport_spi > >> > >> Ok, I looked at check_for_illegal_area() in dma-debug. > >> > >> What check_for_illegal_area() does looks bogus to me with some of I/O > >> remapping hardware. > > > > Can you be more specific about this one? check_for_illegal_area() should > > not depend on any hardware because all it does is checking the machine > > addresses to be mapped. > > The check can't work properly on sparc32. > > Sparc32 always maps the kernel to a fixed physical location, and it > therefore can execute in the identity mapping area of physical memory > like where all the free pages and kmalloc areas live virtually. > > So if we free up some pages within the kernel image (because the > memory is unused, for exmple that's what's happening here with the > extra trap table pages on Robert's machine) we have pages in the free > page pool that are located right inside of the kernel text, data, etc. > > We'll thus need a way to turn off these checks somehow. You could > also augment this check by seeing if there is a backing page, and if > so, whether it is PageReserved or not. That's just one idea. Hmm these checks sound specific and hard to maintain. I think its best to give architectures the option whether to enable this check or not. Joerg -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
