[PATCH 4/4] hvc_dcc: disable user-space access to DCC

On Jul 1, 2015, at 8:00 PM, Stephen Boyd wrote:

quoted

#include <asm/barrier.h>
+#include <asm/hardware/cp14.h>

That's new.

And no one else is using it either.

quoted

+
+static inline void __dcc_initialize(void)
+{
+	u32 val;
+
+	/* Disable user-space access to DCC */
+	val = MRC14(0, c0, c1, 0);
+	val |= 1 << 12; /* DSCR[Comms] */
+	MCR14(val, 0, c0, c1, 0);
+}

Nitpick: We do raw cp14 accesses for other functions in this file, so it
would be nice to be consistent throughout.

I agree, but I didn't want to expand the scope of this patch beyond what it's supposed to do.

quoted

+static inline void __dcc_initialize(void)
+{
+	u32 val;
+
+	/* Disable user-space access to DCC */
+	asm ("mrs %0, mdscr_el1\n"

shouldn't this be volatile?

Well, I figured it wasn't important exactly why these instructions are executed, since it just disables user-space.  I usually get chewed out by someone if I add volatile where it's not needed, so I didn't add it this time.

quoted

+		"	orr %0, %0, #4096\n" /* Set the TDCC bit */

arm64 has some #defines in debug-monitors.h which we should probably
extend to have this bit as a #define too.

Hmmm, the only thing I see in debug_monitors.h that seems applicable are the mdscr_write() and mdscr_read() functions, which seem to overlap cp14.h.