Re: [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region

Hi Peter,

On 13/02/2019 14:25, Peter Zijlstra wrote:

On Wed, Feb 13, 2019 at 02:00:26PM +0000, Will Deacon wrote:

quoted

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

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