[PATCH] cxl/edac: Mask DPA flags in the event record cache key

[Jongwon Lee <ai@linux.com>]

The low bits of the DPA in a General Media or DRAM event record are
flags: bit 0 is VOLATILE and bit 1 is NOT_REPAIRABLE. The trace events
report the DPA with CXL_DPA_MASK applied, but cxl_store_rec_gen_media()
and cxl_store_rec_dram() use the raw value as the xarray key.

User space reads the DPA from the trace event and writes it to the
mem_repair dpa attribute. If the record had any flag set, xa_load()
misses it and the repair fails with -EINVAL. The raw key also lets a
repair go through for a record the device marked NOT_REPAIRABLE, if the
DPA is written with bit 1 set.

Key the records by the masked DPA and skip records marked
NOT_REPAIRABLE.

Co-developed with Claude Code.

Fixes: 0b5ccb0de1e2 ("cxl/edac: Support for finding memory operation attributes from the current boot")
Signed-off-by: Jongwon Lee <ai@linux.com>
---

Notes:
    Tested on QEMU master (b574eaf) with a CXL type 3 device, region
    committed, KASAN and PROVE_LOCKING on. DRAM events injected with
    cxl-inject-dram-event at 0x1001, 0x2000 and 0x3002, then a repair
    requested through mem_repair0..4. Same result for all five:
    
      DPA written   before    after
      0x1000        -EINVAL   ok
      0x1001        ok        -EINVAL
      0x2000        ok        ok
      0x3000        -EINVAL   -EINVAL
      0x3002        ok        -EINVAL
      0x5000        -EINVAL   -EINVAL
    
    No KASAN, lockdep or WARN output. Only DRAM events were injected; the
    General Media path has the same change but was not exercised. Not
    tested on real CXL hardware.

 drivers/cxl/core/edac.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/cxl/core/edac.c b/drivers/cxl/core/edac.c
index 34b81e8dfb..b3dfc33ca6 100644
--- a/drivers/cxl/core/edac.c
+++ b/drivers/cxl/core/edac.c
@@ -918,6 +918,21 @@ struct cxl_mem_repair_attrbs {
 	enum cxl_mem_repair_type repair_type;
 };
 
+/*
+ * The low bits of the event record DPA are flags (VOLATILE, NOT_REPAIRABLE).
+ * Records are looked up by the DPA user space writes back, which comes from
+ * the trace event and has the flags masked off, so key them the same way.
+ */
+static unsigned long cxl_rec_key(const struct cxl_event_media_hdr *hdr)
+{
+	return le64_to_cpu(hdr->phys_addr) & CXL_DPA_MASK;
+}
+
+static bool cxl_rec_not_repairable(const struct cxl_event_media_hdr *hdr)
+{
+	return le64_to_cpu(hdr->phys_addr) & CXL_DPA_NOT_REPAIRABLE;
+}
+
 static struct cxl_event_gen_media *
 cxl_find_rec_gen_media(struct cxl_memdev *cxlmd,
 		       struct cxl_mem_repair_attrbs *attrbs)
@@ -929,7 +944,7 @@ cxl_find_rec_gen_media(struct cxl_memdev *cxlmd,
 		return NULL;
 
 	rec = xa_load(&array_rec->rec_gen_media, attrbs->dpa);
-	if (!rec)
+	if (!rec || cxl_rec_not_repairable(&rec->media_hdr))
 		return NULL;
 
 	if (attrbs->repair_type == CXL_PPR)
@@ -950,7 +965,7 @@ cxl_find_rec_dram(struct cxl_memdev *cxlmd,
 		return NULL;
 
 	rec = xa_load(&array_rec->rec_dram, attrbs->dpa);
-	if (!rec)
+	if (!rec || cxl_rec_not_repairable(&rec->media_hdr))
 		return NULL;
 
 	validity_flags = get_unaligned_le16(rec->media_hdr.validity_flags);
@@ -1105,8 +1120,7 @@ int cxl_store_rec_gen_media(struct cxl_memdev *cxlmd, union cxl_event *evt)
 		return -ENOMEM;
 
 	old_rec = xa_store(&array_rec->rec_gen_media,
-			   le64_to_cpu(rec->media_hdr.phys_addr), rec,
-			   GFP_KERNEL);
+			   cxl_rec_key(&rec->media_hdr), rec, GFP_KERNEL);
 	if (xa_is_err(old_rec)) {
 		kfree(rec);
 		return xa_err(old_rec);
@@ -1135,8 +1149,7 @@ int cxl_store_rec_dram(struct cxl_memdev *cxlmd, union cxl_event *evt)
 		return -ENOMEM;
 
 	old_rec = xa_store(&array_rec->rec_dram,
-			   le64_to_cpu(rec->media_hdr.phys_addr), rec,
-			   GFP_KERNEL);
+			   cxl_rec_key(&rec->media_hdr), rec, GFP_KERNEL);
 	if (xa_is_err(old_rec)) {
 		kfree(rec);
 		return xa_err(old_rec);
-- 
2.55.0