linux-kernel - [PATCH v23 10/19] x86/resctrl: Initialize on-stack struct rmid

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Date: Fri, 28 Jun 2024 14:56:10 -0700
From: Tony Luck <tony.luck@...el.com>
To: Fenghua Yu <fenghua.yu@...el.com>,
	Reinette Chatre <reinette.chatre@...el.com>,
	Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
	Peter Newman <peternewman@...gle.com>,
	James Morse <james.morse@....com>,
	Babu Moger <babu.moger@....com>,
	Drew Fustini <dfustini@...libre.com>,
	Dave Martin <Dave.Martin@....com>
Cc: x86@...nel.org,
	linux-kernel@...r.kernel.org,
	patches@...ts.linux.dev,
	Tony Luck <tony.luck@...el.com>
Subject: [PATCH v23 10/19] x86/resctrl: Initialize on-stack struct rmid_read instances

New semantics rely on some struct rmid_read members having NULL values
to distinguish between the SNC and non-SNC scenarios.  resctrl can thus
no longer rely on this struct not being initialized properly.

Initialize all on-stack declarations of struct rmid_read:
	rdtgroup_mondata_show()
	mbm_update()
	mkdir_mondata_subdir()
to ensure that garbage values from the stack are not passed down
to other functions.

Remove redundant rr->val = 0; from mon_event_read() and rr.first = false;
from mbm_update() since the rmid_read structure is cleared by compiler.

Signed-off-by: Tony Luck <tony.luck@...el.com>
Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
---
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 3 +--
 arch/x86/kernel/cpu/resctrl/monitor.c     | 3 +--
 arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 2 +-
 3 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index 3b9383612c35..4d76ff31a9e0 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -529,7 +529,6 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
 	rr->evtid = evtid;
 	rr->r = r;
 	rr->d = d;
-	rr->val = 0;
 	rr->first = first;
 	rr->arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, evtid);
 	if (IS_ERR(rr->arch_mon_ctx)) {
@@ -557,12 +556,12 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
 {
 	struct kernfs_open_file *of = m->private;
 	struct rdt_domain_hdr *hdr;
+	struct rmid_read rr = {0};
 	struct rdt_mon_domain *d;
 	u32 resid, evtid, domid;
 	struct rdtgroup *rdtgrp;
 	struct rdt_resource *r;
 	union mon_data_bits md;
-	struct rmid_read rr;
 	int ret = 0;
 
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index ff4e74594a19..ca309c93a56b 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -780,9 +780,8 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_mon_domain *dom_mbm)
 static void mbm_update(struct rdt_resource *r, struct rdt_mon_domain *d,
 		       u32 closid, u32 rmid)
 {
-	struct rmid_read rr;
+	struct rmid_read rr = {0};
 
-	rr.first = false;
 	rr.r = r;
 	rr.d = d;
 
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 70d41a8fd788..d0443589cd86 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -3029,10 +3029,10 @@ static int mkdir_mondata_subdir(struct kernfs_node *parent_kn,
 				struct rdt_mon_domain *d,
 				struct rdt_resource *r, struct rdtgroup *prgrp)
 {
+	struct rmid_read rr = {0};
 	union mon_data_bits priv;
 	struct kernfs_node *kn;
 	struct mon_evt *mevt;
-	struct rmid_read rr;
 	char name[32];
 	int ret;
 
-- 
2.45.2