linux-kernel - [PATCH v2] x86/resctrl: Avoid overflow in MB settings in bw

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Message-ID: <1723949d8053aa74da907165dbdc26755f341736.1726492059.git.nert.pinx@gmail.com>
Date: Mon, 16 Sep 2024 15:07:39 +0200
From: Martin Kletzander <nert.pinx@...il.com>
To: Fenghua Yu <fenghua.yu@...el.com>,
	Reinette Chatre <reinette.chatre@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] x86/resctrl: Avoid overflow in MB settings in bw_validate()

When resctrl is mounted with the "mba_MBps" option the default (maximum)
bandwidth is the maximum unsigned value for the type.  However when
using the same value that already exists in the schemata file it is then
rounded up to the bandwidth granularity and overflows to a small number
instead, making it difficult to reset memory bandwidth allocation value
back to its default.

Since the granularity and minimum bandwidth are not used when the
software controller is used (resctrl is mounted with the "mba_MBps"),
skip the rounding up as well and return early from bw_validate().

Signed-off-by: Martin Kletzander <nert.pinx@...il.com>
---
Changes in v2:
 - actually save the value in the output parameter @data

 arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index 50fa1fe9a073..702b1a372e9c 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -48,8 +48,13 @@ static bool bw_validate(char *buf, unsigned long *data, struct rdt_resource *r)
 		return false;
 	}
 
-	if ((bw < r->membw.min_bw || bw > r->default_ctrl) &&
-	    !is_mba_sc(r)) {
+	/* Nothing else to do if software controller is enabled */
+	if (is_mba_sc(r)) {
+		*data = bw;
+		return true;
+	}
+
+	if (bw < r->membw.min_bw || bw > r->default_ctrl) {
 		rdt_last_cmd_printf("MB value %ld out of range [%d,%d]\n", bw,
 				    r->membw.min_bw, r->default_ctrl);
 		return false;
-- 
2.46.0