powerpc: Define set_thread_uses_vas()

A CP_ABORT instruction is required in processes that have mapped a VAS
"paste address" with the intention of using COPY/PASTE instructions.
But since CP_ABORT is expensive, we want to restrict it to only
processes that use/intend to use COPY/PASTE.

Define an interface, set_thread_uses_vas(), that VAS can use to
indicate that the current process opened a send window. During context
switch, issue CP_ABORT only for processes that have the flag set.

Thanks for input from Nick Piggin, Michael Ellerman.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
[mpe: Fix to not use new_thread after _switch() returns]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h
index f5da32f43fed..07ff06e9dae1 100644
--- a/arch/powerpc/include/asm/switch_to.h
+++ b/arch/powerpc/include/asm/switch_to.h
@@ -91,6 +91,8 @@ static inline void clear_task_ebb(struct task_struct *t)
 #endif
 }
 
+extern int set_thread_uses_vas(void);
+
 extern int set_thread_tidr(struct task_struct *t);
 extern void clear_thread_tidr(struct task_struct *t);