On 12/08/16 13:33, Russell King - ARM Linux wrote: > On Fri, Aug 12, 2016 at 06:19:17PM +1000, Nicholas Piggin wrote: >> This patch adds an option which defaults to "y" in cases where we >> could possibly be running Cortex A8 and using Thumb2 instructions. >> In reality the workaround might not be required at all for the kernel >> if virtual instruction memory is linear in physical memory. > > Hmm. > > The main kernel image is guaranteed to be contiguous in physical memory > for all sorts of reasons, so this really isn't a concern for the kernel > itself. I'm not sure being contiguous matters much - looking at the errata doc, the implication is that the branch is supposed to use bits 31:12 of the address of the first page, but under the erratum conditions ends up taking bits 31:12 of the address of the _second_ page instead. There doesn't seem to be any importance of where those pages actually are relative to each other. > Modules, however, are a different matter, as they are mapped in using > individual pages, and are most likely to be non-contiguous in physical > memory. The kernel's module linker knows nothing about this errata, > so it'll generally just fix up the relocations in the most basic of > ways. > > So, I think we should always use this --no-fix-cortex-a8 option where > the linker supports it irrespective of whether we're running on a core > needing this workaround, but we probably need to fix the kernel module > linker to know about this. Given the above, I'm not convinced that sounds safe, but then I can't claim to have fist-hand experience with this bug either. Robin. -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
