On Wed, Feb 13, 2019 at 02:39:22PM +0000, Julien Thierry wrote: > Hi Peter, > > On 13/02/2019 14:25, Peter Zijlstra wrote: > > On Wed, Feb 13, 2019 at 02:00:26PM +0000, Will Deacon wrote: > >> The difference is because getting preempted in the sequence above is > >> triggered off the back of an interrupt. On arm64, and I think also on x86, > >> the user access state (SMAP or PAN) is saved and restored across exceptions > >> but not across context switch. > > > > A quick reading of the SDM seems to suggest the SMAP state is part of > > EFLAGS, which is context switched just fine AFAIK. > > > I fail to see where this is happening when looking at the switch_to() > logic in x86_64.
Yeah, me too.. we obviously preserve EFLAGS for user context, but for kernel-kernel switches we do not seem to preserve it :-(
