[lkml]   [2018]   [Sep]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: Access to non-RAM pages
On Sun, 2 Sep 2018, Linus Torvalds wrote:

> Which basically doesn't happen on x86 in reality. BIOSes just don't put
> MMIO right after the last page of RAM. I think this is why it only
> triggered on Xen, due to some crazy "Xen reacts badly" case where we do
> the speculation into a balloon address.
> So _practically_ this is just a Xen bug, nothing more.

Yeah, and Xen guys are already working on fixing that AFAIK.

> But since in _theory_ you could have MMIO abut regular RAM directly,
> it's worth maybe making sure it's purely theory.

Well, we've been hit by similar/related issue in practice, on x86 machines
where GART aperture is being mapped over physical RAM. For the curious --
see commit 2a3e83c6f ("x86/gart: Exclude GART aperture from vmcore").


Jiri Kosina

 \ /
  Last update: 2018-09-03 08:06    [W:0.105 / U:9.208 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site