Commit 3087a9ff authored Dec 08, 2022 by Wang ShaoBo Committed by Zheng Zengkai Dec 08, 2022

arm64/mpam: correct mbw_max/min if remainder is too large

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I61CPK


CVE: NA

--------------------------------

Writing bandwidth control value to /sys/fs/resctrl/schemata may return
an incorrect value.

For instance:

  $ cat /sys/fs/resctrl/schemata
  L3:0=7fff;1=7fff;2=7fff;3=7fff
  MB:0=100;1=100;2=100;3=100
  $ echo 'MB:0=20' > /sys/fs/resctrl/schemata
  $ cat /sys/fs/resctrl/schemata
  L3:0=7fff;1=7fff;2=7fff;3=7fff
  MB:0=18;1=100;2=100;3=100

Assuming that bwa_wd(given in  MPAMF_MBW_IDR.BWA_WD) is greater than
or equal to 6 (fraction is 64), we can divide mbw_max/min with a
granularity of at least 2 in the range between 0 to 100, if we calculate
mbw_max/min with this formula1:
        mbw_max/min = (Input * range) / Scale

Then we turn to ask for Input with this formula2:
       Input = (mbw_max/min * Scale) / range

But if calculated deviation is too large in formula1, we can no longer
use formula2 to get our original value at a granularity of 2. Therefore,
we need to correct the calculation result of formula1.

Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>
Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>

parent 321e0487

arch/arm64/kernel/mpam/mpam_resctrl.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -2280,6 +2280,8 @@ mpam_update_from_resctrl_cfg(struct mpam_resctrl_res *res,
		case QOS_MBA_MAX_EVENT_ID:
		range = MBW_MAX_BWA_FRACT(res->class->bwa_wd);
		mpam_cfg->mbw_max = (resctrl_cfg * range) / (MAX_MBA_BW - 1);
		/* correct mbw_max if remainder is too large */
		mpam_cfg->mbw_max += ((resctrl_cfg * range) % (MAX_MBA_BW - 1)) / range;
		mpam_cfg->mbw_max =
		(mpam_cfg->mbw_max > range) ? range : mpam_cfg->mbw_max;
		mpam_set_feature(mpam_feat_mbw_max, &mpam_cfg->valid);
		@@ -2287,6 +2289,8 @@ mpam_update_from_resctrl_cfg(struct mpam_resctrl_res *res,
		case QOS_MBA_MIN_EVENT_ID:
		range = MBW_MAX_BWA_FRACT(res->class->bwa_wd);
		mpam_cfg->mbw_min = (resctrl_cfg * range) / (MAX_MBA_BW - 1);
		/* correct mbw_min if remainder is too large */
		mpam_cfg->mbw_min += ((resctrl_cfg * range) % (MAX_MBA_BW - 1)) / range;
		mpam_cfg->mbw_min =
		(mpam_cfg->mbw_min > range) ? range : mpam_cfg->mbw_min;
		mpam_set_feature(mpam_feat_mbw_min, &mpam_cfg->valid);