[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>
diff --git a/arch/arm/vfp/entry.S b/arch/arm/vfp/entry.S
index 7b59554..ca2a5ad 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 f279789..54a2ad6 100644
--- a/arch/arm/vfp/vfp.h
+++ b/arch/arm/vfp/vfp.h
@@ -370,3 +370,7 @@
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 e51e667..d4b7b22 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 @@
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 @@
@ 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 @@
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 @@
@ 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 490d9d1..f1e5951 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -28,7 +28,7 @@
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 @@
{
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 @@
}
/* 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;
}