* [PATCH v9 1/3] cxl/region: Simplify poison_by_decoder() error handling
2026-08-05 5:55 [PATCH v9 0/3] Support zero-sized HDM decoders Richard Cheng
@ 2026-08-05 5:55 ` Richard Cheng
2026-08-05 6:09 ` sashiko-bot
2026-08-05 5:55 ` [PATCH v9 2/3] cxl/hdm: Allow zero sized HDM decoders Richard Cheng
2026-08-05 5:55 ` [PATCH v9 3/3] tools/testing/cxl: Enable zero sized decoders under hb0 Richard Cheng
2 siblings, 1 reply; 6+ messages in thread
From: Richard Cheng @ 2026-08-05 5:55 UTC (permalink / raw)
To: jic23, dave, dave.jiang, vishal.l.verma, djbw, danwilliams,
alison.schofield
Cc: iweiny, ming.li, kaihengf, kobak, vaslot, mochs, newtonl,
kristinc, linux-cxl, linux-kernel, Richard Cheng,
Jonathan Cameron
"rc" carries both an error code and the loop control
signal for device_for_each_child(), so returning it bare is misleading,
the early guards mean "keep walking", not "no error". Zeroing "rc" to
forgive an -EFAULT on a RAM partition adds to that by discarding what
the device actually returned.
Return a literal 0 where the walk should continue, and test the
forgiven case directly instead of rewriting "rc". Give that test a
name, poison_efault_forgiven(), so cxl_get_poison_unmapped() and
poison_by_decoder() spell the same rule the same way. No functional
change.
Suggested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Richard Cheng <icheng@nvidia.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
---
Changelog:
v8 -> v9:
- Add the poison_efault_forgiven() helper and use it in
cxl_get_poison_unmapped()
v7 -> v8:
- New patch. Splits the poison_by_decoder() readability cleanup out
of "cxl/hdm: Allow zero sized HDM decoders" so the functional
change is not mixed with a refactor of pre-existing code.
---
drivers/cxl/core/region.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 1e211542b6b6..45536909cc17 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -2905,6 +2905,16 @@ struct cxl_poison_context {
u64 offset;
};
+/*
+ * A device may answer a Get Poison List request with "physical address
+ * specified is invalid" (-EFAULT). That answer is tolerated for a RAM
+ * partition and the poison walk continues.
+ */
+static inline bool poison_efault_forgiven(int rc, enum cxl_partition_mode mode)
+{
+ return rc == -EFAULT && mode == CXL_PARTMODE_RAM;
+}
+
static int cxl_get_poison_unmapped(struct cxl_memdev *cxlmd,
struct cxl_poison_context *ctx)
{
@@ -2933,7 +2943,7 @@ static int cxl_get_poison_unmapped(struct cxl_memdev *cxlmd,
if (!length)
break;
rc = cxl_mem_get_poison(cxlmd, offset, length, NULL);
- if (rc == -EFAULT && cxlds->part[i].mode == CXL_PARTMODE_RAM)
+ if (poison_efault_forgiven(rc, cxlds->part[i].mode))
continue;
if (rc)
break;
@@ -2950,14 +2960,14 @@ static int poison_by_decoder(struct device *dev, void *arg)
struct cxl_dev_state *cxlds;
struct cxl_memdev *cxlmd;
u64 offset, length;
- int rc = 0;
+ int rc;
if (!is_endpoint_decoder(dev))
- return rc;
+ return 0;
cxled = to_cxl_endpoint_decoder(dev);
if (!cxled->dpa_res)
- return rc;
+ return 0;
cxlmd = cxled_to_memdev(cxled);
cxlds = cxlmd->cxlds;
@@ -2967,18 +2977,14 @@ static int poison_by_decoder(struct device *dev, void *arg)
offset = cxled->dpa_res->start - cxled->skip;
length = cxled->skip;
rc = cxl_mem_get_poison(cxlmd, offset, length, NULL);
- if (rc == -EFAULT && mode == CXL_PARTMODE_RAM)
- rc = 0;
- if (rc)
+ if (rc && !poison_efault_forgiven(rc, mode))
return rc;
}
offset = cxled->dpa_res->start;
length = cxled->dpa_res->end - offset + 1;
rc = cxl_mem_get_poison(cxlmd, offset, length, cxled->cxld.region);
- if (rc == -EFAULT && mode == CXL_PARTMODE_RAM)
- rc = 0;
- if (rc)
+ if (rc && !poison_efault_forgiven(rc, mode))
return rc;
/* Iterate until commit_end is reached */
--
2.43.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH v9 1/3] cxl/region: Simplify poison_by_decoder() error handling
2026-08-05 5:55 ` [PATCH v9 1/3] cxl/region: Simplify poison_by_decoder() error handling Richard Cheng
@ 2026-08-05 6:09 ` sashiko-bot
0 siblings, 0 replies; 6+ messages in thread
From: sashiko-bot @ 2026-08-05 6:09 UTC (permalink / raw)
To: Richard Cheng; +Cc: linux-cxl
Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
New issues:
- [Low] The `poison_efault_forgiven()` helper is restricted to `region.c`, leaving identical open-coded logic in `memdev.c`.
Pre-existing issues:
- [High] Unchecked array index `cxled->part` can be `-1`, leading to an out-of-bounds access on `cxlds->part`.
--
--- Patch [1]: [PATCH v9 1/3] cxl/region: Simplify poison_by_decoder() error handling ---
commit b12d8e90580fa9f2baf0c0dcbd4c6c514e0b2343
Author: Richard Cheng <icheng@nvidia.com>
cxl/region: Simplify poison_by_decoder() error handling
This patch simplifies error handling in cxl_get_poison_unmapped() and
poison_by_decoder() by testing the -EFAULT condition directly and returning
a literal 0 to continue the walk. It introduces poison_efault_forgiven()
to consolidate this logic.
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 1e211542b6b64..45536909cc17d 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -2905,6 +2905,16 @@ struct cxl_poison_context {
> u64 offset;
> };
>
> +/*
> + * A device may answer a Get Poison List request with "physical address
> + * specified is invalid" (-EFAULT). That answer is tolerated for a RAM
> + * partition and the poison walk continues.
> + */
> +static inline bool poison_efault_forgiven(int rc, enum cxl_partition_mode mode)
> +{
> + return rc == -EFAULT && mode == CXL_PARTMODE_RAM;
> +}
[Severity: Low]
Since this helper is defined locally here in region.c, could it be moved to a
shared internal header like drivers/cxl/cxlmem.h?
There is identical open-coded logic in cxl_get_poison_by_memdev() within
memdev.c that could leverage this new helper instead of leaving it open-coded.
[ ... ]
> @@ -2950,14 +2960,14 @@ static int poison_by_decoder(struct device *dev, void *arg)
> struct cxl_dev_state *cxlds;
> struct cxl_memdev *cxlmd;
> u64 offset, length;
> - int rc = 0;
> + int rc;
>
> if (!is_endpoint_decoder(dev))
> - return rc;
> + return 0;
>
> cxled = to_cxl_endpoint_decoder(dev);
> if (!cxled->dpa_res)
> - return rc;
> + return 0;
>
> cxlmd = cxled_to_memdev(cxled);
> cxlds = cxlmd->cxlds;
[Severity: High]
This is a pre-existing issue, but does this code risk an out-of-bounds array
access?
Right after these lines, the code evaluates mode = cxlds->part[cxled->part].mode.
If cxl_dpa_alloc() allocates DPA capacity but cannot strictly map it to a
partition, it can leave cxled->part initialized to -1.
When sysfs invokes poison_by_decoder(), this evaluates cxlds->part[-1].mode
before ensuring cxled->part >= 0. This performs an out-of-bounds read into
memory preceding the array (such as the dpa_res struct) and could silently
corrupt the poison evaluation logic or trigger memory safety warnings.
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260805055524.22311-1-icheng@nvidia.com?part=1
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v9 2/3] cxl/hdm: Allow zero sized HDM decoders
2026-08-05 5:55 [PATCH v9 0/3] Support zero-sized HDM decoders Richard Cheng
2026-08-05 5:55 ` [PATCH v9 1/3] cxl/region: Simplify poison_by_decoder() error handling Richard Cheng
@ 2026-08-05 5:55 ` Richard Cheng
2026-08-05 6:09 ` sashiko-bot
2026-08-05 5:55 ` [PATCH v9 3/3] tools/testing/cxl: Enable zero sized decoders under hb0 Richard Cheng
2 siblings, 1 reply; 6+ messages in thread
From: Richard Cheng @ 2026-08-05 5:55 UTC (permalink / raw)
To: jic23, dave, dave.jiang, vishal.l.verma, djbw, danwilliams,
alison.schofield
Cc: iweiny, ming.li, kaihengf, kobak, vaslot, mochs, newtonl,
kristinc, linux-cxl, linux-kernel, Richard Cheng,
Jonathan Cameron
CXL r4.0 §8.2.4.20.12 ("Committing Decoder Programming") and §14.13.10
("CXL HDM Decoder Zero Size Commit") permit committing an HDM decoder
with size 0. BIOS may commit and lock such decoders so the OS cannot
program regions through them, this is a design choice rather than a spec
requirement.
The kernel rejected these with -ENXIO during port enumeration and
aborted the whole port, so affected systems showed nothing under "cxl
list".
Treat empty decoders as first class instead of special casing them, back
them with a kmalloc'd resource, since the resource tree can't represent
an empty range, and keep the skip and hdm_end accounting intact. Guard
the paths an empty decoder can't serve, e.g. region attach, DPA free,
and poison queries.
Suggested-by: Dan Williams <djbw@kernel.org>
Signed-off-by: Vishal Aslot <vaslot@nvidia.com>
Signed-off-by: Richard Cheng <icheng@nvidia.com>
Reviewed-by: Dan Williams <djbw@kernel.org>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
Changelog:
v8 -> v9:
- Rebase on patch 1's poison_efault_forgiven() helper. The two
-EFAULT tests in poison_by_decoder() now call it. No functional
change.
v7 -> v8:
- Rebase onto the new poison_by_decoder() cleanup patch. The poison
hunk now only wraps the existing code in "if (cxled->part >= 0)";
the -EFAULT/RAM rework moved to patch 1
- cxl_dpa_request_region(): split the declaration from the
allocation
- Add the missing blank line between commit message paragraphs
v6->v7:
- Rebase onto cxl/for-7.3/cxl-type2-test.
v5->v6:
- Comment wording fixups, no functional change: reword cxled_empty()
per Dan Williams' review and tidy the poison-walk comment.
v4->v5:
- Rework per Dan Williams' suggestion: make zero-size DPA
reservations first class instead of bypassing reservation.
cxl_dpa_request_region() returns a kmalloc'd resource for size 0;
cxl_dpa_release_region() kfrees it on teardown. hdm_end now
advances and releases for zero-size decoders under cxl_rwsem.dpa,
and their skip registers are honored.
- Corrections to the posted sketch: add the missing return after
kfree() (use-after-free), use IORESOURCE_MEM flags so
resource_contains() can resolve cxled->part.
- cxl_mem_get_poison() returns success for zero-length queries
before issuing a mailbox command.
- Fully-burned device (all decoders zero-size at DPA 0): cxled->part
cannot resolve; gate poison_by_decoder() queries on part >= 0
(the part[-1] OOB read was already reachable for sized decoders
that fail partition containment) and scan all partitions when the
walk reaches commit_end with nothing mapped (sashiko report).
- Drop v4's poison_by_decoder() restructure and the hdm_end
non-advance approach; superseded by the above.
v3->v4:
- Drop the port->hdm_end advance for zero-size decoders (sashiko AI
review). The write was outside cxl_rwsem.dpa, and advancing the
watermark without a balanced release strands hdm_end and breaks
LIFO teardown. It is also unnecessary -- zero-size committed slots
are trailing and locked, so the in-order check in
__cxl_dpa_reserve() is never reached past them.
v2->v3:
- Advance port->hdm_end for the committed zero-size decoder so a
following committed decoder still passes the in-order check in
__cxl_dpa_reserve() (it was left un-incremented in v2).
- Fold the poison fix into this patch: commit_end may now reference a
zero-size decoder with no DPA resource, so poison_by_decoder() falls
through to run cxl_get_poison_unmapped() and scan the unmapped DPA
tail.
v1->v2:
- Add zero-size committed decoders to the topology instead of
skipping them. Drop v1's -ENOSPC sentinel and the matching
"continue" in devm_cxl_enumerate_decoders(); fall through so
add_hdm_decoder() registers the decoder.
- Set port->commit_end unconditionally for any committed decoder,
not only non-zero-size ones, so subsequent decoders satisfy the
out-of-order check.
- Add an explicit early-return before devm_cxl_dpa_reserve() in the
endpoint-decoder path. __cxl_dpa_reserve() rejects zero-size
decoders
- Spell out TSP and TCB and cite spec sections in commit message
- Reorder series, implementation first
---
drivers/cxl/core/hdm.c | 55 +++++++++++++++++++++++++++------------
drivers/cxl/core/mbox.c | 3 +++
drivers/cxl/core/region.c | 45 +++++++++++++++++++++-----------
drivers/cxl/cxl.h | 10 +++++++
drivers/cxl/port.c | 3 +++
5 files changed, 84 insertions(+), 32 deletions(-)
diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index 0c80b76a5f9b..3b3cfa0f2507 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -240,6 +240,18 @@ static resource_size_t __adjust_skip(struct cxl_dev_state *cxlds,
}
#define release_skip(c, b, l) __adjust_skip((c), (b), (l), NULL)
+static void cxl_dpa_release_region(struct resource *parent,
+ struct resource *res)
+{
+ /* zero sized decoders are not tracked in the resource tree */
+ if (resource_size(res) == 0) {
+ kfree(res);
+ return;
+ }
+
+ __release_region(parent, res->start, resource_size(res));
+}
+
/*
* Must be called in a context that synchronizes against this decoder's
* port ->remove() callback (like an endpoint decoder sysfs attribute)
@@ -256,7 +268,7 @@ static void __cxl_dpa_release(struct cxl_endpoint_decoder *cxled)
/* save @skip_start, before @res is released */
skip_start = res->start - cxled->skip;
- __release_region(&cxlds->dpa_res, res->start, resource_size(res));
+ cxl_dpa_release_region(&cxlds->dpa_res, res);
if (cxled->skip)
release_skip(cxlds, skip_start, cxled->skip);
cxled->skip = 0;
@@ -336,6 +348,26 @@ static int request_skip(struct cxl_dev_state *cxlds,
return -EBUSY;
}
+static struct resource *cxl_dpa_request_region(struct resource *parent,
+ resource_size_t start,
+ resource_size_t n,
+ const char *name)
+{
+ if (!n) {
+ struct resource *res;
+
+ res = kmalloc_obj(*res);
+ if (!res)
+ return NULL;
+
+ *res = DEFINE_RES_NAMED(start, 0, name, IORESOURCE_MEM);
+
+ return res;
+ }
+
+ return __request_region(parent, start, n, name, 0);
+}
+
static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
resource_size_t base, resource_size_t len,
resource_size_t skipped)
@@ -349,12 +381,6 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
lockdep_assert_held_write(&cxl_rwsem.dpa);
- if (!len) {
- dev_warn(dev, "decoder%d.%d: empty reservation attempted\n",
- port->id, cxled->cxld.id);
- return -EINVAL;
- }
-
if (cxled->dpa_res) {
dev_dbg(dev, "decoder%d.%d: existing allocation %pr assigned\n",
port->id, cxled->cxld.id, cxled->dpa_res);
@@ -378,8 +404,8 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
if (rc)
return rc;
}
- res = __request_region(&cxlds->dpa_res, base, len,
- dev_name(&cxled->cxld.dev), 0);
+ res = cxl_dpa_request_region(&cxlds->dpa_res, base, len,
+ dev_name(&cxled->cxld.dev));
if (!res) {
dev_dbg(dev, "decoder%d.%d: failed to reserve allocation\n",
port->id, cxled->cxld.id);
@@ -402,7 +428,8 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
break;
}
- if (cxled->part < 0)
+ /* Empty decoders may not be contained by a partition boundary */
+ if (cxled->part < 0 && resource_size(res))
dev_warn(dev, "decoder%d.%d: %pr does not map any partition\n",
port->id, cxled->cxld.id, res);
@@ -545,7 +572,7 @@ int cxl_dpa_free(struct cxl_endpoint_decoder *cxled)
struct device *dev = &cxled->cxld.dev;
guard(rwsem_write)(&cxl_rwsem.dpa);
- if (!cxled->dpa_res)
+ if (cxled_empty(cxled))
return 0;
if (cxled->cxld.region) {
dev_dbg(dev, "decoder assigned to: %s\n",
@@ -1031,12 +1058,6 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
return -ENXIO;
}
- if (size == 0) {
- dev_warn(&port->dev,
- "decoder%d.%d: Committed with zero size\n",
- port->id, cxld->id);
- return -ENXIO;
- }
port->commit_end = cxld->id;
} else {
if (cxled) {
diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
index 97b1e61ad018..ffd24992273d 100644
--- a/drivers/cxl/core/mbox.c
+++ b/drivers/cxl/core/mbox.c
@@ -1384,6 +1384,9 @@ int cxl_mem_get_poison(struct cxl_memdev *cxlmd, u64 offset, u64 len,
int nr_records = 0;
int rc;
+ if (!len)
+ return 0;
+
ACQUIRE(mutex_intr, lock)(&mds->poison.mutex);
if ((rc = ACQUIRE_ERR(mutex_intr, &lock)))
return rc;
diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 45536909cc17..e6929feb6378 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -2115,7 +2115,7 @@ static int cxl_region_attach(struct cxl_region *cxlr,
return -ENXIO;
}
- if (!cxled->dpa_res) {
+ if (cxled_empty(cxled)) {
dev_dbg(&cxlr->dev, "%s:%s: missing DPA allocation.\n",
dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev));
return -ENXIO;
@@ -2969,24 +2969,31 @@ static int poison_by_decoder(struct device *dev, void *arg)
if (!cxled->dpa_res)
return 0;
- cxlmd = cxled_to_memdev(cxled);
- cxlds = cxlmd->cxlds;
- mode = cxlds->part[cxled->part].mode;
+ /*
+ * Handle the degenerate case of a device with only empty decoders. An
+ * empty decoder can still map a non-zero skip range, so advance the
+ * walk to commit_end either way.
+ */
+ if (cxled->part >= 0) {
+ cxlmd = cxled_to_memdev(cxled);
+ cxlds = cxlmd->cxlds;
+ mode = cxlds->part[cxled->part].mode;
- if (cxled->skip) {
- offset = cxled->dpa_res->start - cxled->skip;
- length = cxled->skip;
- rc = cxl_mem_get_poison(cxlmd, offset, length, NULL);
+ if (cxled->skip) {
+ offset = cxled->dpa_res->start - cxled->skip;
+ length = cxled->skip;
+ rc = cxl_mem_get_poison(cxlmd, offset, length, NULL);
+ if (rc && !poison_efault_forgiven(rc, mode))
+ return rc;
+ }
+
+ offset = cxled->dpa_res->start;
+ length = cxled->dpa_res->end - offset + 1;
+ rc = cxl_mem_get_poison(cxlmd, offset, length, cxled->cxld.region);
if (rc && !poison_efault_forgiven(rc, mode))
return rc;
}
- offset = cxled->dpa_res->start;
- length = cxled->dpa_res->end - offset + 1;
- rc = cxl_mem_get_poison(cxlmd, offset, length, cxled->cxld.region);
- if (rc && !poison_efault_forgiven(rc, mode))
- return rc;
-
/* Iterate until commit_end is reached */
if (cxled->cxld.id == ctx->port->commit_end) {
ctx->offset = cxled->dpa_res->end + 1;
@@ -3008,9 +3015,17 @@ int cxl_get_poison_by_endpoint(struct cxl_port *port)
};
rc = device_for_each_child(&port->dev, &ctx, poison_by_decoder);
- if (rc == 1)
+ if (rc == 1) {
+ /*
+ * No decoder with a sized DPA reservation was walked
+ * (every committed decoder is zero-size): scan all
+ * partitions in full.
+ */
+ if (ctx.part < 0)
+ ctx.part = 0;
rc = cxl_get_poison_unmapped(to_cxl_memdev(port->uport_dev),
&ctx);
+ }
return rc;
}
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index c0e5308e4d1b..cef53d9bd5c0 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -336,6 +336,16 @@ struct cxl_endpoint_decoder {
int pos;
};
+/*
+ * The common case is decoders with no reservation, but also handle
+ * decoders with a zero-sized reservation that firmware may install for
+ * security lockdown purposes.
+ */
+static inline bool cxled_empty(struct cxl_endpoint_decoder *cxled)
+{
+ return !cxled->dpa_res || !resource_size(cxled->dpa_res);
+}
+
/**
* struct cxl_switch_decoder - Switch specific CXL HDM Decoder
* @cxld: base cxl_decoder object
diff --git a/drivers/cxl/port.c b/drivers/cxl/port.c
index 99cf77b6b699..c12fd0b89883 100644
--- a/drivers/cxl/port.c
+++ b/drivers/cxl/port.c
@@ -46,6 +46,9 @@ static int discover_region(struct device *dev, void *unused)
if (cxled->state != CXL_DECODER_STATE_AUTO)
return 0;
+ if (cxled_empty(cxled))
+ return 0;
+
/*
* Region enumeration is opportunistic, if this add-event fails,
* continue to the next endpoint decoder.
--
2.43.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH v9 2/3] cxl/hdm: Allow zero sized HDM decoders
2026-08-05 5:55 ` [PATCH v9 2/3] cxl/hdm: Allow zero sized HDM decoders Richard Cheng
@ 2026-08-05 6:09 ` sashiko-bot
0 siblings, 0 replies; 6+ messages in thread
From: sashiko-bot @ 2026-08-05 6:09 UTC (permalink / raw)
To: Richard Cheng; +Cc: linux-cxl
Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
New issues:
- [High] The teardown logic for 0-sized decoders is broken by an early return, causing a resource leak and permanently breaking the DPA LIFO state machine.
- [Medium] The poison scan for the skip range of an out-of-bounds empty decoder is bypassed, missing hardware error queries.
Pre-existing issues:
- [High] The unmapped poison scan aborts prematurely, missing hardware error queries for subsequent partitions.
--
--- Patch [2]: [PATCH v9 2/3] cxl/hdm: Allow zero sized HDM decoders ---
commit 129bd5c21519972c027d6ca212a8591b5cea7517
Author: Richard Cheng <icheng@nvidia.com>
cxl/hdm: Allow zero sized HDM decoders
This commit allows the kernel to accept and process zero-sized HDM decoders
instead of rejecting them during enumeration. It backs them with a kmalloc'd
resource and guards paths that do not apply to empty decoders.
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 0c80b76a5f9b4..3b3cfa0f25074 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
[ ... ]
> @@ -545,7 +572,7 @@ int cxl_dpa_free(struct cxl_endpoint_decoder *cxled)
> struct device *dev = &cxled->cxld.dev;
>
> guard(rwsem_write)(&cxl_rwsem.dpa);
> - if (!cxled->dpa_res)
> + if (cxled_empty(cxled))
> return 0;
[Severity: High]
Does returning 0 here for 0-sized decoders bypass the release action?
If devm_cxl_dpa_release() is not called for 0-sized decoders, it appears
this would leak the reservation and prevent port->hdm_end from being
decremented, permanently breaking the DPA LIFO state machine for future
teardowns.
[ ... ]
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 45536909cc17d..e6929feb63786 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
[ ... ]
> @@ -2969,24 +2969,31 @@ static int poison_by_decoder(struct device *dev, void *arg)
> if (!cxled->dpa_res)
> return 0;
>
> - cxlmd = cxled_to_memdev(cxled);
> - cxlds = cxlmd->cxlds;
> - mode = cxlds->part[cxled->part].mode;
> + /*
> + * Handle the degenerate case of a device with only empty decoders. An
> + * empty decoder can still map a non-zero skip range, so advance the
> + * walk to commit_end either way.
> + */
> + if (cxled->part >= 0) {
[Severity: Medium]
Will this condition skip checking poison in a valid skip range?
If firmware commits an empty decoder at an out-of-bounds base, cxled->part
would be -1. However, if its skip range is large enough to intersect a
valid partition, skipping this block seems to prevent querying the skipped
DPA space for hardware poison.
> + cxlmd = cxled_to_memdev(cxled);
> + cxlds = cxlmd->cxlds;
> + mode = cxlds->part[cxled->part].mode;
>
> - if (cxled->skip) {
> - offset = cxled->dpa_res->start - cxled->skip;
> - length = cxled->skip;
> - rc = cxl_mem_get_poison(cxlmd, offset, length, NULL);
> + if (cxled->skip) {
> + offset = cxled->dpa_res->start - cxled->skip;
> + length = cxled->skip;
> + rc = cxl_mem_get_poison(cxlmd, offset, length, NULL);
> + if (rc && !poison_efault_forgiven(rc, mode))
> + return rc;
> + }
[ ... ]
> @@ -3008,9 +3015,17 @@ int cxl_get_poison_by_endpoint(struct cxl_port *port)
> };
>
> rc = device_for_each_child(&port->dev, &ctx, poison_by_decoder);
> - if (rc == 1)
> + if (rc == 1) {
> + /*
> + * No decoder with a sized DPA reservation was walked
> + * (every committed decoder is zero-size): scan all
> + * partitions in full.
> + */
> + if (ctx.part < 0)
> + ctx.part = 0;
> rc = cxl_get_poison_unmapped(to_cxl_memdev(port->uport_dev),
> &ctx);
[Severity: High]
This is a pre-existing issue, but does cxl_get_poison_unmapped() abort
prematurely during its scan?
If a preceding partition is fully mapped, length evaluates to 0. In
cxl_get_poison_unmapped():
for (int i = ctx->part; i < cxlds->nr_partitions; i++) {
...
length = res->end - offset + 1;
if (!length)
break;
Using break instead of continue here aborts the loop entirely. Does this
incorrectly skip hardware error queries for any subsequent unmapped
partitions (like PMEM)?
> + }
>
> return rc;
> }
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260805055524.22311-1-icheng@nvidia.com?part=2
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v9 3/3] tools/testing/cxl: Enable zero sized decoders under hb0
2026-08-05 5:55 [PATCH v9 0/3] Support zero-sized HDM decoders Richard Cheng
2026-08-05 5:55 ` [PATCH v9 1/3] cxl/region: Simplify poison_by_decoder() error handling Richard Cheng
2026-08-05 5:55 ` [PATCH v9 2/3] cxl/hdm: Allow zero sized HDM decoders Richard Cheng
@ 2026-08-05 5:55 ` Richard Cheng
2 siblings, 0 replies; 6+ messages in thread
From: Richard Cheng @ 2026-08-05 5:55 UTC (permalink / raw)
To: jic23, dave, dave.jiang, vishal.l.verma, djbw, danwilliams,
alison.schofield
Cc: iweiny, ming.li, kaihengf, kobak, vaslot, mochs, newtonl,
kristinc, linux-cxl, linux-kernel, Richard Cheng,
Jonathan Cameron
The kernel now allows committed zero-size HDM decoders so BIOS can lock
empty decoders; cxl_test needs to exercise that path.
Add a mock_zero_size_decoders module parameter (default off). When set,
the special endpoints under host-bridge0 (cxl_mem.0 and cxl_mem.4)
commit decoders 1 and 2 as zero-size + locked above the decoder[0]
auto-region, mirrored on the parent switch and host bridge. The mocks
take a real zero-size DPA reservation, like enumeration of real
hardware, so commit_end lands on a zero-size decoder and the
reservation, poison-by-endpoint, and teardown paths all run.
Signed-off-by: Vishal Aslot <vaslot@nvidia.com>
Signed-off-by: Richard Cheng <icheng@nvidia.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
---
Changelog:
v8 -> v9:
- No change.
v7 -> v8:
- No change.
v6->v7:
- Rebase onto cxl/for-7.3/cxl-type2-test.
- Integrate mock_zero_size_decoders with special-topology parameter
validation and reject its incompatible use with fail_autoassemble.
v5->v6:
- Reword a mock comment, no functional change.
v4->v5:
- Mirror the v5 core semantics: mock zero-size decoders take a real
zero-size DPA reservation via devm_cxl_dpa_reserve() so
dpa_res/hdm_end/cxled->part match real hardware enumeration and
the poison-by-endpoint walk reaches commit_end.
- Set cxled->state = CXL_DECODER_STATE_AUTO to match
init_hdm_decoder()'s fall-through (undoes the v2 switch to
MANUAL).
- cxld_registry_restore(): reserve unconditionally for enabled
endpoint decoders; enabled now implies reserved, sized or not.
v3->v4:
- No change.
v2->v3:
- Gate the zero-size + locked decoder injection behind a new
mock_zero_size_decoders module parameter (default off). v2
applied it unconditionally on the host-bridge0 auto-region
endpoints, which the region test suite reuses, regressing 7 of
17 cxl unit tests; defaulting off leaves the shared topology
untouched.
v1->v2:
- Replace second_decoder(), third_decoder() with a single
match_decoder_by_index() helper, so all lookups share one
matcher.
- Use DEFINE_RANGE() for the empty range instead of an open-coded
struct.
- Set cxled->state = CXL_DECODER_STATE_MANUAL rather than
STATE_AUTO.
- Set CXL_DECODER_F_LOCK on the mock zero-size decoders to model
the BIOS-burns-slots case.
---
tools/testing/cxl/test/cxl.c | 109 ++++++++++++++++++++++++++++++-----
1 file changed, 94 insertions(+), 15 deletions(-)
diff --git a/tools/testing/cxl/test/cxl.c b/tools/testing/cxl/test/cxl.c
index 8ab2ce1262f3..fff2004a08c8 100644
--- a/tools/testing/cxl/test/cxl.c
+++ b/tools/testing/cxl/test/cxl.c
@@ -18,6 +18,7 @@ static int interleave_arithmetic;
static bool extended_linear_cache;
static bool fail_autoassemble;
static bool type2_test;
+static bool mock_zero_size_decoders;
#define FAKE_QTG_ID 42
@@ -872,14 +873,13 @@ static int cxld_registry_restore(struct cxl_decoder *cxld,
cxld_copy(cxld, &td->cxled.cxld);
cxled->state = td->cxled.state;
cxled->skip = td->cxled.skip;
- if (range_len(&td->dpa_range)) {
- rc = devm_cxl_dpa_reserve(cxled, td->dpa_range.start,
- range_len(&td->dpa_range),
- td->cxled.skip);
- if (rc) {
- init_disabled_mock_decoder(cxld);
- return rc;
- }
+ /* enabled endpoint decoders hold a reservation, sized or not */
+ rc = devm_cxl_dpa_reserve(cxled, td->dpa_range.start,
+ range_len(&td->dpa_range),
+ td->cxled.skip);
+ if (rc) {
+ init_disabled_mock_decoder(cxld);
+ return rc;
}
port->commit_end = cxld->id;
}
@@ -1072,16 +1072,49 @@ static void default_mock_decoder(struct cxl_decoder *cxld)
WARN_ON_ONCE(!cxld_registry_new(cxld));
}
-static int first_decoder(struct device *dev, const void *data)
+static int match_decoder_by_index(struct device *dev, const void *data)
{
+ int target_id = *(const int *)data;
struct cxl_decoder *cxld;
if (!is_switch_decoder(dev))
return 0;
cxld = to_cxl_decoder(dev);
- if (cxld->id == 0)
- return 1;
- return 0;
+ return cxld->id == target_id;
+}
+
+/*
+ * Mock a committed, locked, empty decoder
+ * (CXL r4.0 8.2.4.20.12). Gated by the mock_zero_size_decoders module
+ * param so the default cxl_test topology, shared by the region test
+ * suite, is left undisturbed.
+ */
+static void size_zero_mock_decoder_ep(struct cxl_decoder *cxld, u64 base)
+{
+ struct cxl_endpoint_decoder *cxled = to_cxl_endpoint_decoder(&cxld->dev);
+
+ cxld->hpa_range = DEFINE_RANGE(base, base - 1);
+ cxld->interleave_ways = 2;
+ cxld->interleave_granularity = 4096;
+ cxld->target_type = CXL_DECODER_HOSTONLYMEM;
+ cxld->flags = CXL_DECODER_F_ENABLE | CXL_DECODER_F_LOCK;
+ cxled->state = CXL_DECODER_STATE_AUTO;
+ /* decoder[0] reserved [0, size/2), empty decoders sit at that watermark */
+ devm_cxl_dpa_reserve(cxled, mock_auto_region_size / 2, 0, 0);
+ cxld->commit = mock_decoder_commit;
+ cxld->reset = mock_decoder_reset;
+}
+
+static void size_zero_mock_decoder_sw(struct cxl_decoder *cxld, u64 base,
+ int level)
+{
+ cxld->flags = CXL_DECODER_F_ENABLE | CXL_DECODER_F_LOCK;
+ cxld->target_type = CXL_DECODER_HOSTONLYMEM;
+ cxld->interleave_ways = level == 0 ? 2 : 1;
+ cxld->interleave_granularity = 4096;
+ cxld->hpa_range = DEFINE_RANGE(base, base - 1);
+ cxld->commit = mock_decoder_commit;
+ cxld->reset = mock_decoder_reset;
}
enum cxld_init_type {
@@ -1114,7 +1147,7 @@ static enum cxld_init_type get_decoder_init_type(struct cxl_decoder *cxld,
* See 'cxl list -BMPu -m cxl_mem.0,cxl_mem.4'
*/
if (!is_endpoint_decoder(&cxld->dev) || !hb0 || pdev->id % 4 ||
- pdev->id > 4 || cxld->id > 0)
+ pdev->id > 4 || cxld->id > (mock_zero_size_decoders ? 2 : 0))
return MOCK_DECODER_INIT_DEFAULT;
return type2_test ? MOCK_DECODER_INIT_TYPE2_AUTO :
@@ -1147,6 +1180,7 @@ static void mock_init_hdm_type2_cxled(struct cxl_endpoint_decoder *cxled,
struct cxl_port *root_port;
struct device *dev;
u64 base;
+ int id = 0;
base = window->base_hpa;
cxld->hpa_range = (struct range) {
@@ -1172,7 +1206,7 @@ static void mock_init_hdm_type2_cxled(struct cxl_endpoint_decoder *cxled,
*/
dport = port->parent_dport;
root_port = dport->port;
- dev = device_find_child(&root_port->dev, NULL, first_decoder);
+ dev = device_find_child(&root_port->dev, &id, match_decoder_by_index);
/*
* Ancestor ports are guaranteed to be enumerated before
* @port, and all ports have at least one decoder.
@@ -1232,6 +1266,20 @@ static void mock_init_hdm_type3_cxled(struct cxl_endpoint_decoder *cxled,
base = window->base_hpa;
if (extended_linear_cache)
base += mock_auto_region_size;
+
+ /*
+ * With mock_zero_size_decoders, decoders 1 and 2 of the special
+ * endpoints mock committed, locked, empty decoders above the
+ * decoder[0] auto-region (CXL r4.0 8.2.4.20.12). commit_end then
+ * points at a zero-size decoder, exercising the zero-size
+ * reservation and poison-by-endpoint code paths.
+ */
+ if (cxld->id == 1 || cxld->id == 2) {
+ size_zero_mock_decoder_ep(cxld, base);
+ port->commit_end = cxld->id;
+ WARN_ON_ONCE(!cxld_registry_new(cxld));
+ return;
+ }
cxld->hpa_range = (struct range) {
.start = base,
.end = base + mock_auto_region_size - 1,
@@ -1255,9 +1303,11 @@ static void mock_init_hdm_type3_cxled(struct cxl_endpoint_decoder *cxled,
*/
iter = port;
for (i = 0; i < 2; i++) {
+ int id = 0;
+
dport = iter->parent_dport;
iter = dport->port;
- dev = device_find_child(&iter->dev, NULL, first_decoder);
+ dev = device_find_child(&iter->dev, &id, match_decoder_by_index);
/*
* Ancestor ports are guaranteed to be enumerated before
* @port, and all ports have at least one decoder.
@@ -1307,6 +1357,26 @@ static void mock_init_hdm_type3_cxled(struct cxl_endpoint_decoder *cxled,
cxld_registry_update(cxld);
put_device(dev);
+
+ if (!mock_zero_size_decoders)
+ continue;
+
+ /*
+ * Mirror the endpoint: commit the next two switch decoders
+ * as zero-size + locked so the empty-decoder layout extends
+ * end-to-end through the switch and host bridge.
+ */
+ for (id = 1; id <= 2; id++) {
+ dev = device_find_child(&iter->dev, &id,
+ match_decoder_by_index);
+ if (WARN_ON(!dev))
+ continue;
+ cxld = to_cxl_decoder(dev);
+ size_zero_mock_decoder_sw(cxld, base, i);
+ iter->commit_end = id;
+ cxld_registry_update(cxld);
+ put_device(dev);
+ }
}
}
@@ -2085,6 +2155,12 @@ static bool __init have_multiple_modparms(void)
count++;
if (type2_test)
count++;
+ if (mock_zero_size_decoders)
+ count++;
+
+ /* Zero-size decoders require decoder[0] to preserve commit order. */
+ if (fail_autoassemble && mock_zero_size_decoders)
+ return true;
return count > 1;
}
@@ -2493,6 +2569,9 @@ module_param(fail_autoassemble, bool, 0444);
MODULE_PARM_DESC(fail_autoassemble, "Simulate missing member of an auto-region");
module_param(type2_test, bool, 0444);
MODULE_PARM_DESC(type2_test, "Enable type 2 support testing");
+module_param(mock_zero_size_decoders, bool, 0444);
+MODULE_PARM_DESC(mock_zero_size_decoders,
+ "Mock committed, locked, empty decoders under host-bridge0");
module_init(cxl_test_init);
module_exit(cxl_test_exit);
MODULE_LICENSE("GPL v2");
--
2.43.0
^ permalink raw reply related [flat|nested] 6+ messages in thread