linux-kernel - [PATCH v2] fs/resctrl: fix domid loss precision issue

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Date: Tue, 12 Mar 2024 15:53:49 +0800
From: Rex Nie <rex.nie@...uarmicro.com>
To: james.morse@....com
Cc: fenghua.yu@...el.com,
	reinette.chatre@...el.com,
	ilpo.jarvinen@...ux.intel.com,
	linux-kernel@...r.kernel.org,
	Rex Nie <rex.nie@...uarmicro.com>
Subject: [PATCH v2] fs/resctrl: fix domid loss precision issue

Below statement from mkdir_mondata_subdir function will loss precision,
because it assigns int to 14 bits bitfield.
	priv.u.domid = d->id;

On some platforms(e.g.,x86), the max cache_id is the amount of L3 caches,
so it is not in the range of 0x3fff. But some platforms use higher
cache_id, e.g., arm uses cache_id as locator for cache MSC. This will
cause below issue if cache_id > 0x3fff likes:
/sys/fs/resctrl/mon_groups/p1/mon_data/mon_L3_1048564 # cat llc_occupancy
cat: read error: No such file or directory

This is the call trace when cat llc_occupancy:
rdtgroup_mondata_show()
	domid = md.u.domid
	d = resctrl_arch_find_domain(r, domid)

d is null here because of lossing precision

Signed-off-by: Rex Nie <rex.nie@...uarmicro.com>
---
 fs/resctrl/internal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index 7a6f46b4edd0..096317610949 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -94,7 +94,7 @@ union mon_data_bits {
 	struct {
 		unsigned int rid		: 10;
 		enum resctrl_event_id evtid	: 8;
-		unsigned int domid		: 14;
+		u32				domid;
 	} u;
 };
 
-- 
2.34.1