On Fri 03-07-20 15:29:22, Jann Horn wrote:

On Fri, Jul 3, 2020 at 1:30 PM Michal Hocko [off-list ref] wrote:

quoted

On Fri 03-07-20 10:34:09, Catangiu, Adrian Costin wrote:

quoted

This patch adds logic to the kernel power code to zero out contents of
all MADV_WIPEONSUSPEND VMAs present in the system during its transition
to any suspend state equal or greater/deeper than Suspend-to-memory,
known as S3.

How does the application learn that its memory got wiped? S2disk is an
async operation and it can happen at any time during the task execution.
So how does the application work to prevent from corrupted state - e.g.
when suspended between two memory loads?

You can do it seqlock-style, kind of - you reserve the first byte of
the page or so as a "is this page initialized" marker, and after every
read from the page, you do a compiler barrier and check whether that
byte has been cleared.

This is certainly possible yet wery awkwar interface to use IMHO.
MADV_EXTERNALY_VOLATILE would express the actual semantic much better.
I might not still understand the expected usecase but if the target
application has to be changed anyway then why not simply use a
transparent and proper signaling mechanism like poll on a fd. That would
be certainly a more natural and less error prone programming interface.

-- 
Michal Hocko
SUSE Labs