On Tue, Jul 11, 2017 at 6:58 AM, Brian Gerst <brgerst@xxxxxxxxx> wrote: > On Mon, Jul 10, 2017 at 3:50 PM, Tom Lendacky <thomas.lendacky@xxxxxxx> wrote: >> On 7/8/2017 7:57 AM, Brian Gerst wrote: >>> On Fri, Jul 7, 2017 at 9:39 AM, Tom Lendacky <thomas.lendacky@xxxxxxx> >> >> I originally had a check for SME here in a previous version of the >> patch. Thomas Gleixner recommended removing the check so that the code >> path was always exercised regardless of the state of SME in order to >> better detect issues: >> >> http://marc.info/?l=linux-kernel&m=149803067811436&w=2 > > Looking a bit closer, this shortcut doesn't set the caching > attributes. So it's probably best to get rid of it anyways. Also > note, there is a corresponding check in iounmap(). Could that cause regressions if a driver relies on (write-through) cacheable access to the VGA frame buffer RAM or an read-only cached access to an option ROM but now gets uncached access? I also tried to find out whether we can stop mapping the ISA MMIO area into the linear mapping, but at least the VGA code uses VGA_MAP_MEM() to get access to the same pointers. I'm pretty sure this got copied incorrectly into most other architectures, but it is definitely still used on x86 with vga16fb/vgacon/mdacon. On the plus side, I see that removing this code path will end up restoring MMIOTRACE support for the ISA MMIO range that was apparently removed by accident in commit d61fc44853f4 ("x86: mmiotrace, preview 2") in linux-2.6.27. Arnd
