AMD systems support zero CBM (capacity bit mask) for cache 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")
Co-developed-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Babu Moger <babu.moger@amd.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: James Morse <james.morse@arm.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.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;

> AMD systems support zero CBM (capacity bit mask) for cache 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")
> Co-developed-by: Stephane Eranian <eranian@google.com>
> Signed-off-by: Stephane Eranian <eranian@google.com>
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> Reviewed-by: Ingo Molnar <mingo@kernel.org>
> Reviewed-by: James Morse <james.morse@arm.com>
> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>

Reviewed-by: Fenghua Yu <fenghua.yu@intel.com>