On Tue, Jul 11, 2017 at 6:58 AM, Brian Gerst [off-list ref] wrote:
On Mon, Jul 10, 2017 at 3:50 PM, Tom Lendacky [off-list ref] wrote:
quoted
On 7/8/2017 7:57 AM, Brian Gerst wrote:
quoted
On Fri, Jul 7, 2017 at 9:39 AM, Tom Lendacky [off-list ref]
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