Re: [PATCH] powerpc/vas: do not set uses_vas for kernel windows

Nicholas Piggin [npiggin@gmail.com] wrote:

cp_abort is only required or user windows, because kernel context
must not be preempted between a copy/paste pair.

Yes, that is a good optimization.

Without this patch, the init task gets used_vas set when it runs
the nx842_powernv_init initcall, which opens windows for kernel
usage.

used_vas is then never cleared anywhere, so it gets propagated
into all other tasks. It's a property of the address space, so it
should really be cleared when a new mm is created (or in dup_mmap
if the mmaps are marked as VM_DONTCOPY). For now we seem to have
no such driver, so leave that for another patch.

If the parent process has the paste address mapped, the child inherits
those mappings - so we can't clear the ->used_vas in a process until
it has unmapped all the send windows right?

If VM_DONCOPY is set, then we can clear it.

Cc: Sukadev Bhattiprolu <redacted>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Reviewed-by: Sukadev Bhattiprolu <redacted>