On Fri 03-07-20 15:29:22, Jann Horn wrote: > On Fri, Jul 3, 2020 at 1:30 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Fri 03-07-20 10:34:09, Catangiu, Adrian Costin wrote: > > > 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
