On Tue, Jul 29, 2014 at 2:57 PM, Russell King - ARM Linux <[email protected]> wrote: > On Mon, Jul 28, 2014 at 11:57:16PM +0400, Konstantin Khlebnikov wrote: >> On Mon, Jul 28, 2014 at 11:42 PM, Russell King - ARM Linux >> <[email protected]> wrote: >> > On Mon, Jul 28, 2014 at 11:29:39PM +0400, Konstantin Khlebnikov wrote: >> >> Ok, before switching from identity mapping to normal mapping kernel must >> >> switch instruction pointer from physical address to virtual. >> > >> > "switch instruction pointer from physical address to virtual." >> > >> > There's no such distinction for the instruction pointer. >> >> I know. I mean "logically". >> > ... >> >> Sorry but I'm really look so dumb? Maybe it's true, it's almost >> midnight at my side. > > When you use language which suggests a lack of understanding, then > I will explain things. > >> > It doesn't matter, provided the kernel text and data in the virtual >> > address space are not overwritten by the identity mapping. If it >> > ends up in the vmalloc or IO space, that should not be a problem. >> >> In my case it's been overwritten. >> And it always happens when PHYS_OFFSET >= PAGE_OFFSET >> because in case of LPAE idmap always overwrites 1Gb at once. > > Right, I now see what you're getting at. Here's a better description > which I've used when committing your patch. I've only taken patch 2 > at the present time. > >
Ok. Thank you for your time. > > On LPAE, each level 1 (pgd) page table entry maps 1GiB, and the level 2 > (pmd) entries map 2MiB. > > When the identity mapping is created on LPAE, the pgd pointers are copied > from the swapper_pg_dir. If we find that we need to modify the contents > of a pmd, we allocate a new empty pmd table and insert it into the > appropriate 1GB slot, before then filling it with the identity mapping. > > However, if the 1GB slot covers the kernel lowmem mappings, we obliterate > those mappings. > > When replacing a PMD, first copy the old PMD contents to the new PMD, so > that we preserve the existing mappings in the 1GiB region, particularly > the mappings of the kernel itself. > > > -- > FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up > according to speedtest.net. -- 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/
