ARM: vfp: fix vfp_sync_state()

The more I look at vfp_sync_state(), the more I believe it's trying
to do its job in a really obscure way.

Essentially, last_VFP_context[] tracks who owns the state in the VFP
hardware.  If last_VFP_context[] is the context for the thread which
we're interested in, then the VFP hardware has context which is not
saved in the software state - so we need to bring the software state
up to date.

If last_VFP_context[] is for some other thread, we really don't care
what state the VFP hardware is in; it doesn't contain any information
pertinent to the thread we're trying to deal with - so don't touch
the hardware.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 16 insertions, 20 deletions

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index f60a5400a25b..86a57aeeda4a 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -444,32 +444,28 @@ void vfp_sync_state(struct thread_info *thread)
 void vfp_sync_state(struct thread_info *thread)
 {
         unsigned int cpu = get_cpu();
-        u32 fpexc = fmrx(FPEXC);
 
         /*
-         * If VFP is enabled, the previous state was already saved and
-         * last_VFP_context updated.
+         * If the thread we're interested in is the current owner of the
+         * hardware VFP state, then we need to save its state.
          */
-        if (fpexc & FPEXC_EN)
-                goto out;
-
-        if (!last_VFP_context[cpu])
-                goto out;
+        if (last_VFP_context[cpu] == &thread->vfpstate) {
+                u32 fpexc = fmrx(FPEXC);
 
-        /*
-         * Save the last VFP state on this CPU.
-         */
-        fmxr(FPEXC, fpexc | FPEXC_EN);
-        vfp_save_state(last_VFP_context[cpu], fpexc);
-        fmxr(FPEXC, fpexc);
+                /*
+                 * Save the last VFP state on this CPU.
+                 */
+                fmxr(FPEXC, fpexc | FPEXC_EN);
+                vfp_save_state(&thread->vfpstate, fpexc | FPEXC_EN);
+                fmxr(FPEXC, fpexc & ~FPEXC_EN);
 
-        /*
-         * Set the context to NULL to force a reload the next time the thread
-         * uses the VFP.
-         */
-        last_VFP_context[cpu] = NULL;
+                /*
+                 * Set the context to NULL to force a reload the next time
+                 * the thread uses the VFP.
+                 */
+                last_VFP_context[cpu] = NULL;
+        }
 
-out:
         put_cpu();
 }
 #endif