gru: fix istatus race in GRU tlb dropin

TLB dropins require updates to the CBR instruction istatus field.  This is
needed to resolve race conditions in the chip.

The code currently uses the user address of the CBR.  This works but opens
up additional endcases related to stealing of contexts and accessing the
CBR from tasks that do not have access to the user address space.  (Some
of this non-user task access is debug code that is not currently being
pushed to the community).

User CBRs are also directly accessible using the kernel mapping of the
CBR.  Change the TLB dropin code to use the the kernel mapping of the CBR.
Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/misc/sgi-gru/grufault.c

@@ -122,22 +122,11 @@ static void gru_unlock_gts(struct gru_thread_state *gts)
  * is necessary to prevent the user from seeing a stale cb.istatus that will
  * change as soon as the TFH restart is complete. Races may cause an
  * occasional failure to clear the cb.istatus, but that is ok.
- *
- * If the cb address is not valid (should not happen, but...), nothing
- * bad will happen.. The get_user()/put_user() will fail but there
- * are no bad side-effects.
  */
-static void gru_cb_set_istatus_active(unsigned long __user *cb)
+static void gru_cb_set_istatus_active(struct gru_instruction_bits *cbk)
 {
-	union {
-		struct gru_instruction_bits bits;
-		unsigned long dw;
-	} u;
-
-	if (cb) {
-		get_user(u.dw, cb);
-		u.bits.istatus = CBS_ACTIVE;
-		put_user(u.dw, cb);
+	if (cbk) {
+		cbk->istatus = CBS_ACTIVE;
 	}
 }
 
@@ -322,9 +311,9 @@ static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
  */
 static int gru_try_dropin(struct gru_thread_state *gts,
 			  struct gru_tlb_fault_handle *tfh,
-			  unsigned long __user *cb)
+			  struct gru_instruction_bits *cbk)
 {
-	int pageshift = 0, asid, write, ret, atomic = !cb;
+	int pageshift = 0, asid, write, ret, atomic = !cbk;
 	unsigned long gpa = 0, vaddr = 0;
 
 	/*
@@ -347,7 +336,7 @@ static int gru_try_dropin(struct gru_thread_state *gts,
 	}
 	if (tfh->state == TFHSTATE_IDLE)
 		goto failidle;
-	if (tfh->state == TFHSTATE_MISS_FMM && cb)
+	if (tfh->state == TFHSTATE_MISS_FMM && cbk)
 		goto failfmm;
 
 	write = (tfh->cause & TFHCAUSE_TLB_MOD) != 0;
@@ -378,7 +367,7 @@ static int gru_try_dropin(struct gru_thread_state *gts,
 			goto failupm;
 		}
 	}
-	gru_cb_set_istatus_active(cb);
+	gru_cb_set_istatus_active(cbk);
 	tfh_write_restart(tfh, gpa, GAA_RAM, vaddr, asid, write,
 			  GRU_PAGESIZE(pageshift));
 	STAT(tlb_dropin);
@@ -392,7 +381,7 @@ static int gru_try_dropin(struct gru_thread_state *gts,
 	/* No asid (delayed unload). */
 	STAT(tlb_dropin_fail_no_asid);
 	gru_dbg(grudev, "FAILED no_asid tfh: 0x%p, vaddr 0x%lx\n", tfh, vaddr);
-	if (!cb)
+	if (!cbk)
 		tfh_user_polling_mode(tfh);
 	else
 		gru_flush_cache(tfh);
@@ -415,17 +404,18 @@ static int gru_try_dropin(struct gru_thread_state *gts,
 failnoexception:
 	/* TFH status did not show exception pending */
 	gru_flush_cache(tfh);
-	if (cb)
-		gru_flush_cache(cb);
+	if (cbk)
+		gru_flush_cache(cbk);
 	STAT(tlb_dropin_fail_no_exception);
-	gru_dbg(grudev, "FAILED non-exception tfh: 0x%p, status %d, state %d\n", tfh, tfh->status, tfh->state);
+	gru_dbg(grudev, "FAILED non-exception tfh: 0x%p, status %d, state %d\n",
+		tfh, tfh->status, tfh->state);
 	return 0;
 
 failidle:
 	/* TFH state was idle  - no miss pending */
 	gru_flush_cache(tfh);
-	if (cb)
-		gru_flush_cache(cb);
+	if (cbk)
+		gru_flush_cache(cbk);
 	STAT(tlb_dropin_fail_idle);
 	gru_dbg(grudev, "FAILED idle tfh: 0x%p, state %d\n", tfh, tfh->state);
 	return 0;
@@ -439,7 +429,7 @@ static int gru_try_dropin(struct gru_thread_state *gts,
 
 failactive:
 	/* Range invalidate active. Switch to UPM iff atomic */
-	if (!cb)
+	if (!cbk)
 		tfh_user_polling_mode(tfh);
 	else
 		gru_flush_cache(tfh);
@@ -512,7 +502,7 @@ irqreturn_t gru_intr(int irq, void *dev_id)
 
 static int gru_user_dropin(struct gru_thread_state *gts,
 			   struct gru_tlb_fault_handle *tfh,
-			   unsigned long __user *cb)
+			   void *cb)
 {
 	struct gru_mm_struct *gms = gts->ts_gms;
 	int ret;
@@ -538,7 +528,7 @@ int gru_handle_user_call_os(unsigned long cb)
 {
 	struct gru_tlb_fault_handle *tfh;
 	struct gru_thread_state *gts;
-	unsigned long __user *cbp;
+	void *cbk;
 	int ucbnum, cbrnum, ret = -EINVAL;
 
 	STAT(call_os);
@@ -548,7 +538,6 @@ int gru_handle_user_call_os(unsigned long cb)
 	ucbnum = get_cb_number((void *)cb);
 	if ((cb & (GRU_HANDLE_STRIDE - 1)) || ucbnum >= GRU_NUM_CB)
 		return -EINVAL;
-	cbp = (unsigned long *)cb;
 
 	gts = gru_find_lock_gts(cb);
 	if (!gts)
@@ -583,7 +572,9 @@ int gru_handle_user_call_os(unsigned long cb)
 		gru_unload_context(gts, 1);
 	} else if (gts->ts_gru) {
 		tfh = get_tfh_by_index(gts->ts_gru, cbrnum);
-		ret = gru_user_dropin(gts, tfh, cbp);
+		cbk = get_gseg_base_address_cb(gts->ts_gru->gs_gru_base_vaddr,
+				gts->ts_ctxnum, ucbnum);
+		ret = gru_user_dropin(gts, tfh, cbk);
 	}
 exit:
 	gru_unlock_gts(gts);