linux-kernel - [PATCH v2 01/10] x86/resctrl: Fix min_cbm

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Date:   Mon, 1 Aug 2022 15:55:47 -0500
From:   Babu Moger <babu.moger@....com>
To:     <fenghua.yu@...el.com>, <reinette.chatre@...el.com>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>
CC:     <eranian@...gle.com>, <dave.hansen@...ux.intel.com>,
        <x86@...nel.org>, <hpa@...or.com>, <corbet@....net>,
        <hpa@...or.com>, <linux-kernel@...r.kernel.org>,
        <linux-doc@...r.kernel.org>
Subject: [PATCH v2 01/10] x86/resctrl: Fix min_cbm_bits for AMD

AMD systems support zero CBM (capacity bit mask) for L3 allocation.
That is 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 of another check in cbm_validate():

	if ((zero_bit - first_bit) < r->cache.min_cbm_bits)

The default value of 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
	$ cat /sys/fs/resctrl/info/last_cmd_status
	  Need at least 1 bits in the mask

Fix the issue by initializing the min_cbm_bits to 0 for AMD. Also remove
the default setting of min_cbm_bits and initialize it separately.

After the fix
	$ cd /sys/fs/resctrl
	$ mkdir foo
	$ cd foo
	$ echo L3:0=0 > schemata
	$ cat /sys/fs/resctrl/info/last_cmd_status
	  ok

Link: https://lore.kernel.org/lkml/20220517001234.3137157-1-eranian@google.com/
Fixes: 316e7f901f5a ("x86/resctrl: Add struct rdt_cache::arch_has_{sparse, empty}_bitmaps")
Signed-off-by: Stephane Eranian <eranian@...gle.com>
Signed-off-by: Babu Moger <babu.moger@....com>
---
 arch/x86/kernel/cpu/resctrl/core.c |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index bb1c3f5f60c8..a5c51a14fbce 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -66,9 +66,6 @@ struct rdt_hw_resource rdt_resources_all[] = {
 			.rid			= RDT_RESOURCE_L3,
 			.name			= "L3",
 			.cache_level		= 3,
-			.cache = {
-				.min_cbm_bits	= 1,
-			},
 			.domains		= domain_init(RDT_RESOURCE_L3),
 			.parse_ctrlval		= parse_cbm,
 			.format_str		= "%d=%0*x",
@@ -83,9 +80,6 @@ struct rdt_hw_resource rdt_resources_all[] = {
 			.rid			= RDT_RESOURCE_L2,
 			.name			= "L2",
 			.cache_level		= 2,
-			.cache = {
-				.min_cbm_bits	= 1,
-			},
 			.domains		= domain_init(RDT_RESOURCE_L2),
 			.parse_ctrlval		= parse_cbm,
 			.format_str		= "%d=%0*x",
@@ -877,6 +871,7 @@ static __init void rdt_init_res_defs_intel(void)
 			r->cache.arch_has_sparse_bitmaps = false;
 			r->cache.arch_has_empty_bitmaps = false;
 			r->cache.arch_has_per_cpu_cfg = false;
+			r->cache.min_cbm_bits = 1;
 		} else if (r->rid == RDT_RESOURCE_MBA) {
 			hw_res->msr_base = MSR_IA32_MBA_THRTL_BASE;
 			hw_res->msr_update = mba_wrmsr_intel;
@@ -897,6 +892,7 @@ 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;