powerpc: Add support for userspace P9 copy paste
The copy paste facility introduced in POWER9 provides an optimised
mechanism for a userspace application to copy a cacheline. This is
provided by a pair of instructions, copy and paste, while a third,
cp_abort (copy paste abort), provides a clean up of the state in case of
a failure.
The copy instruction will read a 128 byte cacheline and store it in an
internal buffer. The subsequent paste instruction will store this
internal buffer to memory and set a CR field if the paste succeeds.
Since the state of the copy paste buffer is internal (and not
architecturally visible), in the unlikely event of a context switch, the
state cannot be stored and the paste should therefore fail.
The cp_abort instruction exists to fail and clean up any such
interrupted copy paste sequence and is to be called by the kernel as
part of the context switch. Doing so prevents data from a preceding copy
in one process leaking into the paste of another.
This code enables use of the cp_abort instruction if a supported
processor is detected.
NOTE: this is for userspace only, not in kernel, and does not deal
with KVM guests.
Patch created with much assistance from Michael Neuling
<mikey@neuling.org>
Signed-off-by: Chris Smart <chris@distroguy.com>
Reviewed-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 39a79c8..4fd4922 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -37,6 +37,7 @@
#include <asm/hw_irq.h>
#include <asm/context_tracking.h>
#include <asm/tm.h>
+#include <asm/ppc-opcode.h>
/*
* System calls.
@@ -509,6 +510,14 @@
ldarx r6,0,r1
END_FTR_SECTION_IFSET(CPU_FTR_STCX_CHECKS_ADDRESS)
+BEGIN_FTR_SECTION
+/*
+ * A cp_abort (copy paste abort) here ensures that when context switching, a
+ * copy from one process can't leak into the paste of another.
+ */
+ PPC_CP_ABORT
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
+
#ifdef CONFIG_PPC_BOOK3S
/* Cancel all explict user streams as they will have no use after context
* switch and will stop the HW from creating streams itself
