On Fri, Aug 12, 2016 at 03:21:41PM +0200, Oleg Nesterov wrote:

Whats really interesting is that I still fail to understand do we really
need this hack, iiuc you are not sure too, and Michael didn't bother to
explain why a bogus zero from anon memory is worse than other problems
caused by SIGKKILL from oom-kill.c.

vhost thread will die, but vcpu thread is going on.  If it's memory is
corrupted because vhost read 0 and uses that as an array index, it can
do things like corrupt the disk, so it can't be restarted.

But I really wish we didn't need this special-casing.  Can't PTEs be
made invalid on oom instead of pointing them at the zero page? And then
won't memory accesses trigger pagefaults instead of returning 0? That
would make regular copy_from_user machinery do the right thing,
making vhost stop running as appropriate.

-- 
MST

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