[RFC PATCH 2/6] arm_mpam: Fix read-back of cloned resource controls under CDP emulation

[Dave Martin <Dave.Martin@arm.com>]

When reading resource control values through a resctrl schemata
file, the index into the configuration array in the MPAM driver
is currently translated incorrectly.

This means that when resctrl is mounted with the "cdp" option, the
wrong array entry may be returned or an out-of-bounds array access
may occur when reading back of control values for the MB resource.

Fix it by translating the index for affected resources as if they
were "DATA" resources.  ("CODE" would also work, but because
resctrl_arch_update_one() clones schemata writes across "CODE" and
"DATA" for affected resources, it does not matter which one is
read.)

Signed-off-by: Dave Martin <Dave.Martin@arm.com>

---

This issue was introduced by the non-upstream commit
"arm_mpam: resctrl: Improve CDP emulation"

(commit b097a6193546dbbd27cd19d7e16e1e750ebb030f in
git://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/snapshot/v6.12-rc1 )
---
 drivers/platform/arm64/mpam/mpam_resctrl.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/platform/arm64/mpam/mpam_resctrl.c b/drivers/platform/arm64/mpam/mpam_resctrl.c
index 76ddbce0ea9c..30f2caec11d7 100644
--- a/drivers/platform/arm64/mpam/mpam_resctrl.c
+++ b/drivers/platform/arm64/mpam/mpam_resctrl.c
@@ -1097,6 +1097,14 @@ u32 resctrl_arch_get_config(struct rdt_resource *r, struct rdt_ctrl_domain *d,
 	dom = container_of(d, struct mpam_resctrl_dom, resctrl_ctrl_dom);
 	cprops = &res->class->props;
 
+	/*
+	 * When CDP is enabled, but the resource doesn't support it,
+	 * the control is cloned across both partids.
+	 * Pick one at random to read:
+	 */
+	if (mpam_resctrl_hide_cdp(r->rid))
+		type = CDP_DATA;
+
 	partid = resctrl_get_config_index(closid, type);
 	cfg = &dom->comp->cfg[partid];
 
-- 
2.34.1