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Message-Id: <20250530122852.10139-1-ming.li@zohomail.com>
Date: Fri, 30 May 2025 20:28:52 +0800
From: Li Ming <ming.li@...omail.com>
To: dave@...olabs.net,
jonathan.cameron@...wei.com,
dave.jiang@...el.com,
alison.schofield@...el.com,
vishal.l.verma@...el.com,
ira.weiny@...el.com,
dan.j.williams@...el.com,
shiju.jose@...wei.com
Cc: linux-cxl@...r.kernel.org,
linux-kernel@...r.kernel.org,
Li Ming <ming.li@...omail.com>
Subject: [RFC PATCH 1/1] cxl/edac: Fix the min_scrub_cycle of a region miscalculation
When trying to update the scrub_cycle value of a cxl region, which means
updating the scrub_cycle value of each memdev under a cxl region. cxl
driver needs to guarantee the new scrub_cycle value is greater than the
min_scrub_cycle value of a memdev, otherwise the updating operation will
fail(Per Table 8-223 in CXL r3.2 section 8.2.10.9.11.1).
Current implementation logic of getting the min_scrub_cycle value of a
cxl region is that getting the min_scrub_cycle value of each memdevs
under the cxl region, then using the minimum min_scrub_cycle value as
the region's min_scrub_cycle. Checking if the new scrub_cycle value is
greater than this value. If yes, updating the new scrub_cycle value to
each memdevs. The issue is that the new scrub_cycle value is possibly
greater than the minimum min_scrub_cycle value of all memdevs but less
than the maximum min_scrub_cycle value of all memdevs if memdevs have
a different min_scrub_cycle value. The updating operation will always
fail on these memdevs which have a greater min_scrub_cycle than the new
scrub_cycle.
The correct implementation logic is to get the maximum value of these
memdevs' min_scrub_cycle, check if the new scrub_cycle value is greater
than the value. If yes, the new scrub_cycle value is fit for the region.
The change also impacts the result of
cxl_patrol_scrub_get_min_scrub_cycle(), the interface returned the
minimum min_scrub_cycle value among all memdevs under the region before
the change. The interface will return the maximum min_scrub_cycle value
among all memdevs under the region with the change.
Signed-off-by: Li Ming <ming.li@...omail.com>
---
I made this change based on my understanding on the SPEC and current CXL
EDAC code, but I am not sure if it is a bug or it is designed this way.
base-commit: 9f153b7fb5ae45c7d426851f896487927f40e501 cxl/next
---
drivers/cxl/core/edac.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/cxl/core/edac.c b/drivers/cxl/core/edac.c
index 2cbc664e5d62..ad243cfe00e7 100644
--- a/drivers/cxl/core/edac.c
+++ b/drivers/cxl/core/edac.c
@@ -103,10 +103,10 @@ static int cxl_scrub_get_attrbs(struct cxl_patrol_scrub_context *cxl_ps_ctx,
u8 *cap, u16 *cycle, u8 *flags, u8 *min_cycle)
{
struct cxl_mailbox *cxl_mbox;
- u8 min_scrub_cycle = U8_MAX;
struct cxl_region_params *p;
struct cxl_memdev *cxlmd;
struct cxl_region *cxlr;
+ u8 min_scrub_cycle = 0;
int i, ret;
if (!cxl_ps_ctx->cxlr) {
@@ -133,8 +133,12 @@ static int cxl_scrub_get_attrbs(struct cxl_patrol_scrub_context *cxl_ps_ctx,
if (ret)
return ret;
+ /*
+ * The min_scrub_cycle of a region is the maximum value among
+ * the min_scrub_cycle of all the memdevs under the region.
+ */
if (min_cycle)
- min_scrub_cycle = min(*min_cycle, min_scrub_cycle);
+ min_scrub_cycle = max(*min_cycle, min_scrub_cycle);
}
if (min_cycle)
--
2.34.1
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