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Commit f968dc11 authored by Reinette Chatre's avatar Reinette Chatre Committed by Thomas Gleixner
Browse files

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: d9b48c86 ("x86/intel_rdt: Display resource groups' allocations in bytes")
Reported-by: default avatarChen Yu <yu.c.chen@intel.com>
Signed-off-by: default avatarReinette Chatre <reinette.chatre@intel.com>
Signed-off-by: default avatarFenghua Yu <fenghua.yu@intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarChen Yu <yu.c.chen@intel.com>
Cc: "H Peter Anvin" <hpa@zytor.com>
Cc: "Tony Luck" <tony.luck@intel.com>
Cc: "Xiaochen Shen" <xiaochen.shen@intel.com>
Link: https://lkml.kernel.org/r/20180904174614.26682-1-yu.c.chen@intel.com
Link: https://lkml.kernel.org/r/1537048707-76280-3-git-send-email-fenghua.yu@intel.com
parent 753694a8

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c

+10 −4
Original line number Diff line number Diff line
@@ -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;