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Subject[Patch 15/29] GRU - Fix prefetch and speculation bugs
From: Jack Steiner <steiner@sgi.com>

Fix several bugs related to prefetch, ordering & speculation:

- GRU cch_allocate() instruction causes cacheable memory
to be created. Add a barriers to prevent speculation
from prefetching data before it exists.
- Add memory barriers before cache-flush instructions to ensure
that previously stored data is included in the line flushed to memory.

Signed-off-by: Jack Steiner <steiner@sgi.com>

---
drivers/misc/sgi-gru/gru_instructions.h | 1 +
drivers/misc/sgi-gru/grufault.c | 2 ++
drivers/misc/sgi-gru/gruhandles.c | 22 ++++++++++++++++++++--
drivers/misc/sgi-gru/grukservices.c | 10 ++++++----
drivers/misc/sgi-gru/grumain.c | 9 +++++++++
5 files changed, 38 insertions(+), 6 deletions(-)
Index: linux/drivers/misc/sgi-gru/gru_instructions.h
===================================================================
--- linux.orig/drivers/misc/sgi-gru/gru_instructions.h 2009-11-20 09:32:25.000000000 -0600
+++ linux/drivers/misc/sgi-gru/gru_instructions.h 2009-11-20 09:32:33.000000000 -0600
@@ -325,6 +325,7 @@ static inline void gru_flush_cache(void
static inline void gru_start_instruction(struct gru_instruction *ins, int op32)
{
gru_ordered_store_int(ins, op32);
+ mb();
gru_flush_cache(ins);
}

Index: linux/drivers/misc/sgi-gru/grufault.c
===================================================================
--- linux.orig/drivers/misc/sgi-gru/grufault.c 2009-11-20 09:32:33.000000000 -0600
+++ linux/drivers/misc/sgi-gru/grufault.c 2009-11-20 09:32:33.000000000 -0600
@@ -333,6 +333,7 @@ static int gru_try_dropin(struct gru_thr
*/
if (tfh->status != TFHSTATUS_EXCEPTION) {
gru_flush_cache(tfh);
+ sync_core();
if (tfh->status != TFHSTATUS_EXCEPTION)
goto failnoexception;
STAT(tfh_stale_on_fault);
@@ -599,6 +600,7 @@ int gru_get_exception_detail(unsigned lo
cbrnum = thread_cbr_number(gts, ucbnum);
cbe = get_cbe_by_index(gts->ts_gru, cbrnum);
gru_flush_cache(cbe); /* CBE not coherent */
+ sync_core(); /* make sure we are have current data */
excdet.opc = cbe->opccpy;
excdet.exopc = cbe->exopccpy;
excdet.ecause = cbe->ecause;
Index: linux/drivers/misc/sgi-gru/gruhandles.c
===================================================================
--- linux.orig/drivers/misc/sgi-gru/gruhandles.c 2009-11-20 09:32:30.000000000 -0600
+++ linux/drivers/misc/sgi-gru/gruhandles.c 2009-11-20 09:32:33.000000000 -0600
@@ -91,9 +91,18 @@ static int wait_instruction_complete(voi

int cch_allocate(struct gru_context_configuration_handle *cch)
{
+ int ret;
+
cch->opc = CCHOP_ALLOCATE;
start_instruction(cch);
- return wait_instruction_complete(cch, cchop_allocate);
+ ret = wait_instruction_complete(cch, cchop_allocate);
+
+ /*
+ * Stop speculation into the GSEG being mapped by the previous ALLOCATE.
+ * The GSEG memory does not exist until the ALLOCATE completes.
+ */
+ sync_core();
+ return ret;
}

int cch_start(struct gru_context_configuration_handle *cch)
@@ -112,9 +121,18 @@ int cch_interrupt(struct gru_context_con

int cch_deallocate(struct gru_context_configuration_handle *cch)
{
+ int ret;
+
cch->opc = CCHOP_DEALLOCATE;
start_instruction(cch);
- return wait_instruction_complete(cch, cchop_deallocate);
+ ret = wait_instruction_complete(cch, cchop_deallocate);
+
+ /*
+ * Stop speculation into the GSEG being unmapped by the previous
+ * DEALLOCATE.
+ */
+ sync_core();
+ return ret;
}

int cch_interrupt_sync(struct gru_context_configuration_handle
Index: linux/drivers/misc/sgi-gru/grukservices.c
===================================================================
--- linux.orig/drivers/misc/sgi-gru/grukservices.c 2009-11-20 09:32:32.000000000 -0600
+++ linux/drivers/misc/sgi-gru/grukservices.c 2009-11-20 09:32:33.000000000 -0600
@@ -395,6 +395,7 @@ int gru_get_cb_exception_detail(void *cb
cbrnum = thread_cbr_number(bs->bs_kgts, get_cb_number(cb));
cbe = get_cbe(GRUBASE(cb), cbrnum);
gru_flush_cache(cbe); /* CBE not coherent */
+ sync_core();
excdet->opc = cbe->opccpy;
excdet->exopc = cbe->exopccpy;
excdet->ecause = cbe->ecause;
@@ -461,9 +462,10 @@ int gru_check_status_proc(void *cb)
int ret;

ret = gen->istatus;
- if (ret != CBS_EXCEPTION)
- return ret;
- return gru_retry_exception(cb);
+ if (ret == CBS_EXCEPTION)
+ ret = gru_retry_exception(cb);
+ rmb();
+ return ret;

}

@@ -475,7 +477,7 @@ int gru_wait_proc(void *cb)
ret = gru_wait_idle_or_exception(gen);
if (ret == CBS_EXCEPTION)
ret = gru_retry_exception(cb);
-
+ rmb();
return ret;
}

Index: linux/drivers/misc/sgi-gru/grumain.c
===================================================================
--- linux.orig/drivers/misc/sgi-gru/grumain.c 2009-11-20 09:32:31.000000000 -0600
+++ linux/drivers/misc/sgi-gru/grumain.c 2009-11-20 09:32:33.000000000 -0600
@@ -499,6 +499,9 @@ static void gru_load_context_data(void *
memset(cbe + i * GRU_HANDLE_STRIDE, 0,
GRU_CACHE_LINE_BYTES);
}
+ /* Flush CBE to hide race in context restart */
+ mb();
+ gru_flush_cache(cbe + i * GRU_HANDLE_STRIDE);
cb += GRU_HANDLE_STRIDE;
}

@@ -519,6 +522,12 @@ static void gru_unload_context_data(void
cb = gseg + GRU_CB_BASE;
cbe = grubase + GRU_CBE_BASE;
length = hweight64(dsrmap) * GRU_DSR_AU_BYTES;
+
+ /* CBEs may not be coherent. Flush them from cache */
+ for_each_cbr_in_allocation_map(i, &cbrmap, scr)
+ gru_flush_cache(cbe + i * GRU_HANDLE_STRIDE);
+ mb(); /* Let the CL flush complete */
+
gru_prefetch_context(gseg, cb, cbe, cbrmap, length);

for_each_cbr_in_allocation_map(i, &cbrmap, scr) {


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