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.
And Peter A. didn't seem to suggest that this transfer of the eflags was happening without them being saved on the stack through exception handling. What am I missing? Thanks, -- Julien Thierry
