linux-kernel - [PATCH] x86/resctrl: fix min_cbm

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Date:   Sun, 15 May 2022 22:50:55 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     fenghua.yu@...el.com, reinette.chatre@...el.com, babu.moger@....com
Subject: [PATCH] x86/resctrl: fix min_cbm_bits for AMD

AMD supports cbm with no bits set as reflected in rdt_init_res_defs_amd() by:

	r->cache.arch_has_empty_bitmaps = true;

However given the unified code in cbm_validate(), checking for

    val == 0 && !arch_has_empty_bitmaps

is not enough because you also have in cbm_validate():
	if ((zero_bit - first_bit) < r->cache.min_cbm_bits)

Default value for if r->cache.min_cbm_bits = 1

Leading to:

$ cd /sys/fs/resctrl
$ mkdir foo
$ cd foo
$ echo L3:0=0 > schemata
-bash: echo: write error: Invalid argument

Patch initializes r->cache.min_cbm_bits to 0 for AMD.

Signed-off-by: Stephane Eranian <eranian@...gle.com>
---
 arch/x86/kernel/cpu/resctrl/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index bb1c3f5f60c8..14782361ebb7 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -897,6 +897,7 @@ static __init void rdt_init_res_defs_amd(void)
 			r->cache.arch_has_sparse_bitmaps = true;
 			r->cache.arch_has_empty_bitmaps = true;
 			r->cache.arch_has_per_cpu_cfg = true;
+			r->cache.min_cbm_bits = 0;
 		} else if (r->rid == RDT_RESOURCE_MBA) {
 			hw_res->msr_base = MSR_IA32_MBA_BW_BASE;
 			hw_res->msr_update = mba_wrmsr_amd;
-- 
2.36.0.550.gb090851708-goog