[ARM] 4111/1: Allow VFP to work with thread migration on SMP

The current lazy saving of the VFP registers is no longer possible
with thread migration on SMP. This patch implements a per-CPU
vfp-state pointer and the saving of the VFP registers at every context
switch. The registers restoring is still performed in a lazy way.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

4 files changed, 55 insertions, 6 deletions

diff --git a/arch/arm/vfp/entry.S b/arch/arm/vfp/entry.S
index 7b595547c1c8..ca2a5ad19ea6 100644
--- a/arch/arm/vfp/entry.S
+++ b/arch/arm/vfp/entry.S
@@ -25,6 +25,7 @@
 do_vfp:
         enable_irq
         ldr     r4, .LCvfp
+        ldr     r11, [r10, #TI_CPU]     @ CPU number
         add     r10, r10, #TI_VFPSTATE  @ r10 = workspace
         ldr     pc, [r4]                @ call VFP entry point
 
diff --git a/arch/arm/vfp/vfp.h b/arch/arm/vfp/vfp.h
index f2797896e6d5..54a2ad6d9ca2 100644
--- a/arch/arm/vfp/vfp.h
+++ b/arch/arm/vfp/vfp.h
@@ -370,3 +370,7 @@ struct op {
         u32 (* const fn)(int dd, int dn, int dm, u32 fpscr);
         u32 flags;
 };
+
+#ifdef CONFIG_SMP
+extern void vfp_save_state(void *location, u32 fpexc);
+#endif
diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
index e51e6679c402..d4b7b229631d 100644
--- a/arch/arm/vfp/vfphw.S
+++ b/arch/arm/vfp/vfphw.S
@@ -65,6 +65,7 @@
 @  r2  = faulted PC+4
 @  r9  = successful return
 @  r10 = vfp_state union
+@  r11 = CPU number
 @  lr  = failure return
 
         .globl  vfp_support_entry
@@ -79,7 +80,7 @@ vfp_support_entry:
         DBGSTR1 "enable %x", r10
         ldr     r3, last_VFP_context_address
         orr     r1, r1, #FPEXC_ENABLE   @ user FPEXC has the enable bit set
-        ldr     r4, [r3]                @ last_VFP_context pointer
+        ldr     r4, [r3, r11, lsl #2]   @ last_VFP_context pointer
         bic     r5, r1, #FPEXC_EXCEPTION @ make sure exceptions are disabled
         cmp     r4, r10
         beq     check_for_exception     @ we are returning to the same
@@ -91,7 +92,9 @@ vfp_support_entry:
                                         @ exceptions, so we can get at the
                                         @ rest of it
 
+#ifndef CONFIG_SMP
         @ Save out the current registers to the old thread state
+        @ No need for SMP since this is not done lazily
 
         DBGSTR1 "save old state %p", r4
         cmp     r4, #0
@@ -105,10 +108,11 @@ vfp_support_entry:
         stmia   r4, {r1, r5, r6, r8}    @ save FPEXC, FPSCR, FPINST, FPINST2
                                         @ and point r4 at the word at the
                                         @ start of the register dump
+#endif
 
 no_old_VFP_process:
         DBGSTR1 "load state %p", r10
-        str     r10, [r3]               @ update the last_VFP_context pointer
+        str     r10, [r3, r11, lsl #2]  @ update the last_VFP_context pointer
                                         @ Load the saved state back into the VFP
         VFPFLDMIA r10                   @ reload the working registers while
                                         @ FPEXC is in a safe state
@@ -162,6 +166,24 @@ process_exception:
                                         @ required. If not, the user code will
                                         @ retry the faulted instruction
 
+#ifdef CONFIG_SMP
+        .globl  vfp_save_state
+        .type   vfp_save_state, %function
+vfp_save_state:
+        @ Save the current VFP state
+        @ r0 - save location
+        @ r1 - FPEXC
+        DBGSTR1 "save VFP state %p", r0
+        VFPFMRX r2, FPSCR               @ current status
+        VFPFMRX r3, FPINST              @ FPINST (always there, rev0 onwards)
+        tst     r1, #FPEXC_FPV2         @ is there an FPINST2 to read?
+        VFPFMRX r12, FPINST2, NE        @ FPINST2 if needed - avoids reading
+                                        @ nonexistant reg on rev0
+        VFPFSTMIA r0                    @ save the working registers
+        stmia   r0, {r1, r2, r3, r12}   @ save FPEXC, FPSCR, FPINST, FPINST2
+        mov     pc, lr
+#endif
+
 last_VFP_context_address:
         .word   last_VFP_context
 
diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 490d9d18a7d1..f1e5951dc721 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -28,7 +28,7 @@ void vfp_testing_entry(void);
 void vfp_support_entry(void);
 
 void (*vfp_vector)(void) = vfp_testing_entry;
-union vfp_state *last_VFP_context;
+union vfp_state *last_VFP_context[NR_CPUS];
 
 /*
  * Dual-use variable.
@@ -41,13 +41,35 @@ static int vfp_notifier(struct notifier_block *self, unsigned long cmd, void *v)
 {
         struct thread_info *thread = v;
         union vfp_state *vfp;
+        __u32 cpu = thread->cpu;
 
         if (likely(cmd == THREAD_NOTIFY_SWITCH)) {
+                u32 fpexc = fmrx(FPEXC);
+
+#ifdef CONFIG_SMP
+                /*
+                 * On SMP, if VFP is enabled, save the old state in
+                 * case the thread migrates to a different CPU. The
+                 * restoring is done lazily.
+                 */
+                if ((fpexc & FPEXC_ENABLE) && last_VFP_context[cpu]) {
+                        vfp_save_state(last_VFP_context[cpu], fpexc);
+                        last_VFP_context[cpu]->hard.cpu = cpu;
+                }
+                /*
+                 * Thread migration, just force the reloading of the
+                 * state on the new CPU in case the VFP registers
+                 * contain stale data.
+                 */
+                if (thread->vfpstate.hard.cpu != cpu)
+                        last_VFP_context[cpu] = NULL;
+#endif
+
                 /*
                  * Always disable VFP so we can lazily save/restore the
                  * old state.
                  */
-                fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_ENABLE);
+                fmxr(FPEXC, fpexc & ~FPEXC_ENABLE);
                 return NOTIFY_DONE;
         }
 
@@ -68,8 +90,8 @@ static int vfp_notifier(struct notifier_block *self, unsigned long cmd, void *v)
         }
 
         /* flush and release case: Per-thread VFP cleanup. */
-        if (last_VFP_context == vfp)
-                last_VFP_context = NULL;
+        if (last_VFP_context[cpu] == vfp)
+                last_VFP_context[cpu] = NULL;
 
         return NOTIFY_DONE;
 }