[PATCH 2/9] x86/intel_rdt: Fix size reporting of MBA resource

[Fenghua Yu]

From: Reinette Chatre <reinette.chatre@xxxxxxxxx>

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

[  151.193447] divide error: 0000 [#1] SMP PTI
[  151.197743] CPU: 93 PID: 1929 Comm: cat Not tainted 4.19.0-rc2-debug-rdt+ #25
[  151.205070] Hardware name: Dell Inc. PowerEdge R640/0CRT1G, BIOS 1.3.7 02/08/2018
[  151.212783] RIP: 0010:rdtgroup_cbm_to_size+0x7e/0xa0
[  151.237172] RSP: 0018:ffffb3454f90bd88 EFLAGS: 00010246
[  151.242538] RAX: 00000000023c0000 RBX: 0000000000000000 RCX: 0000000000000003
[  151.249878] RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000003
[  151.257213] RBP: ffff96ff0089e000 R08: 0000000000000000 R09: 0000000000aaaaaa
[  151.264544] R10: ffffb3454f90bd8c R11: 00000000ffffffff R12: ffffffffb5028910
[  151.271887] R13: ffffffffb5028910 R14: 0000000000000064 R15: ffff96ff0089e000
[  151.279217] FS:  00007f95a623a500(0000) GS:ffff97170f9c0000(0000) knlGS:0000000000000000
[  151.287532] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  151.293432] CR2: 00007f95a6217000 CR3: 00000023f696c003 CR4: 00000000007606e0
[  151.300766] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  151.308094] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  151.315426] PKRU: 55555554
[  151.318212] Call Trace:
[  151.320732]  rdtgroup_size_show+0x11a/0x1d0
[  151.325039]  seq_read+0xd8/0x3b0
[  151.328363]  __vfs_read+0x36/0x170
[  151.331857]  vfs_read+0x89/0x130
[  151.335179]  ksys_read+0x52/0xc0
[  151.338500]  do_syscall_64+0x5b/0x180
[  151.342261]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

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")
Link: https://lkml.kernel.org/r/20180904174614.26682-1-yu.c.chen@xxxxxxxxx
Reported-by: Chen Yu <yu.c.chen@xxxxxxxxx>
Tested-by: Chen Yu <yu.c.chen@xxxxxxxxx>
Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Signed-off-by: Fenghua Yu <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;
-- 
2.19.0