[PATCH Utopic SRU 4/4] cxl: Fix PSL error due to duplicate segment table entries

tim.gardner at canonical.com tim.gardner at canonical.com
Thu Oct 30 13:15:32 UTC 2014


From: Ian Munsie <imunsie at au1.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1387523

In certain circumstances the PSL (Power Service Layer, which provides
translation services for CXL hardware) can send an interrupt for a
segment miss that the kernel has already handled. This can happen if
multiple translations for the same segment are queued in the PSL before
the kernel has restarted the first translation.

The CXL driver does not expect this situation and does not check if a
segment had already been handled. This could cause a duplicate segment
table entry which in turn caused a PSL error taking down the card.

This patch fixes the issue by checking for existing entries in the
segment table that match the segment we are trying to insert, so as to
avoid inserting duplicate entries.

Signed-off-by: Ian Munsie <imunsie at au1.ibm.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
(cherry picked from commit eb01d4c2388ce3b5bcc120d0f72912117ed7599d)
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 drivers/misc/cxl/fault.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/drivers/misc/cxl/fault.c b/drivers/misc/cxl/fault.c
index cb4f323..c99e896 100644
--- a/drivers/misc/cxl/fault.c
+++ b/drivers/misc/cxl/fault.c
@@ -21,11 +21,20 @@
 
 #include "cxl.h"
 
-/* This finds a free SSTE for the given SLB */
+static bool sste_matches(struct cxl_sste *sste, struct copro_slb *slb)
+{
+	return ((sste->vsid_data == cpu_to_be64(slb->vsid)) &&
+		(sste->esid_data == cpu_to_be64(slb->esid)));
+}
+
+/*
+ * This finds a free SSTE for the given SLB, or returns NULL if it's already in
+ * the segment table.
+ */
 static struct cxl_sste* find_free_sste(struct cxl_context *ctx,
 				       struct copro_slb *slb)
 {
-	struct cxl_sste *primary, *sste;
+	struct cxl_sste *primary, *sste, *ret = NULL;
 	unsigned int mask = (ctx->sst_size >> 7) - 1; /* SSTP0[SegTableSize] */
 	unsigned int entry;
 	unsigned int hash;
@@ -38,15 +47,19 @@ static struct cxl_sste* find_free_sste(struct cxl_context *ctx,
 	primary = ctx->sstp + (hash << 3);
 
 	for (entry = 0, sste = primary; entry < 8; entry++, sste++) {
-		if (!(be64_to_cpu(sste->esid_data) & SLB_ESID_V))
-			return sste;
+		if (!ret && !(be64_to_cpu(sste->esid_data) & SLB_ESID_V))
+			ret = sste;
+		if (sste_matches(sste, slb))
+			return NULL;
 	}
+	if (ret)
+		return ret;
 
 	/* Nothing free, select an entry to cast out */
-	sste = primary + ctx->sst_lru;
+	ret = primary + ctx->sst_lru;
 	ctx->sst_lru = (ctx->sst_lru + 1) & 0x7;
 
-	return sste;
+	return ret;
 }
 
 static void cxl_load_segment(struct cxl_context *ctx, struct copro_slb *slb)
@@ -57,12 +70,15 @@ static void cxl_load_segment(struct cxl_context *ctx, struct copro_slb *slb)
 
 	spin_lock_irqsave(&ctx->sste_lock, flags);
 	sste = find_free_sste(ctx, slb);
+	if (!sste)
+		goto out_unlock;
 
 	pr_devel("CXL Populating SST[%li]: %#llx %#llx\n",
 			sste - ctx->sstp, slb->vsid, slb->esid);
 
 	sste->vsid_data = cpu_to_be64(slb->vsid);
 	sste->esid_data = cpu_to_be64(slb->esid);
+out_unlock:
 	spin_unlock_irqrestore(&ctx->sste_lock, flags);
 }
 
-- 
1.9.1





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