[tip:x86/urgent] x86/intel_rdt: Fix size reporting of MBA resource

[tip-bot for Reinette Chatre]

Commit-ID:  f968dc119a159a95628a20de2a2dcc913d0a82d7
Gitweb:     https://git.kernel.org/tip/f968dc119a159a95628a20de2a2dcc913d0a82d7
Author:     Reinette Chatre <reinette.chatre@xxxxxxxxx>
AuthorDate: Sat, 15 Sep 2018 14:58:20 -0700
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 18 Sep 2018 23:38:05 +0200

x86/intel_rdt: Fix size reporting of MBA resource

Chen Yu reported a divide-by-zero error when accessing the 'size'
resctrl file when a MBA resource is enabled.

divide error: 0000 [#1] SMP PTI
CPU: 93 PID: 1929 Comm: cat Not tainted 4.19.0-rc2-debug-rdt+ #25
RIP: 0010:rdtgroup_cbm_to_size+0x7e/0xa0
Call Trace:
rdtgroup_size_show+0x11a/0x1d0
seq_read+0xd8/0x3b0

Quoting Chen Yu's report: This is because for MB resource, the
r->cache.cbm_len is zero, thus calculating size in rdtgroup_cbm_to_size()
will trigger the exception.

Fix this issue in the 'size' file by getting correct memory bandwidth value
which is in MBps when MBA software controller is enabled or in percentage
when MBA software controller is disabled.

Fixes: d9b48c86eb38 ("x86/intel_rdt: Display resource groups' allocations in bytes")
Reported-by: Chen Yu <yu.c.chen@xxxxxxxxx>
Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Chen Yu <yu.c.chen@xxxxxxxxx>
Cc: "H Peter Anvin" <hpa@xxxxxxxxx>
Cc: "Tony Luck" <tony.luck@xxxxxxxxx>
Cc: "Xiaochen Shen" <xiaochen.shen@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20180904174614.26682-1-yu.c.chen@xxxxxxxxx
Link: https://lkml.kernel.org/r/1537048707-76280-3-git-send-email-fenghua.yu@xxxxxxxxx

---
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index b799c00bef09..32e8bbdf2400 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -1155,8 +1155,8 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
 	struct rdt_resource *r;
 	struct rdt_domain *d;
 	unsigned int size;
-	bool sep = false;
-	u32 cbm;
+	bool sep;
+	u32 ctrl;
 
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
 	if (!rdtgrp) {
@@ -1174,6 +1174,7 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
 	}
 
 	for_each_alloc_enabled_rdt_resource(r) {
+		sep = false;
 		seq_printf(s, "%*s:", max_name_width, r->name);
 		list_for_each_entry(d, &r->domains, list) {
 			if (sep)
@@ -1181,8 +1182,13 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
 			if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
 				size = 0;
 			} else {
-				cbm = d->ctrl_val[rdtgrp->closid];
-				size = rdtgroup_cbm_to_size(r, d, cbm);
+				ctrl = (!is_mba_sc(r) ?
+						d->ctrl_val[rdtgrp->closid] :
+						d->mbps_val[rdtgrp->closid]);
+				if (r->rid == RDT_RESOURCE_MBA)
+					size = ctrl;
+				else
+					size = rdtgroup_cbm_to_size(r, d, ctrl);
 			}
 			seq_printf(s, "%d=%u", d->id, size);
 			sep = true;