[PATCH][RFC] x86/intel_rdt: Do not display size for non-CAT resource

[Chen Yu]

On a platform with MB resource enabled, a divided-by-zero
exception is triggered when accessing 'size':

[  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

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 by not exposing 'size' for non-CAT resources.

Fixes: d9b48c86eb38 ("x86/intel_rdt: Display resource groups'
allocations in bytes")
Cc: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
---
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index b799c00bef09..53fd07b2f61a 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -1329,7 +1329,7 @@ static struct rftype res_common_files[] = {
 		.mode		= 0444,
 		.kf_ops		= &rdtgroup_kf_single_ops,
 		.seq_show	= rdtgroup_size_show,
-		.fflags		= RF_CTRL_BASE,
+		.fflags		= RF_CTRL_INFO | RFTYPE_RES_CACHE,
 	},
 
 };
-- 
2.17.1