Re: [PATCH v2] x86/resctrl: Fix zero cbm for AMD in cbm_validate

Fenghua Yu
2022-05-17T16:33:11Z

Hi, Eranian,

On Mon, May 16, 2022 at 05:12:34PM -0700, Stephane Eranian wrote:
> AMD supports cbm with no bits set as reflected in rdt_init_res_defs_amd() by:
...
> @@ -107,6 +107,10 @@ static bool cbm_validate(char *buf, u32 *data, struct rdt_resource *r)
> first_bit = find_first_bit(&val, cbm_len);
> zero_bit = find_next_zero_bit(&val, cbm_len, first_bit);
>
> + /* no need to check bits if arch supports no bits set */
> + if (r->cache.arch_has_empty_bitmaps && val == 0)
> + goto done;
> +
> /* Are non-contiguous bitmaps allowed? */
> if (!r->cache.arch_has_sparse_bitmaps &&
> (find_next_bit(&val, cbm_len, zero_bit) < cbm_len)) {
> @@ -119,7 +123,7 @@ static bool cbm_validate(char *buf, u32 *data, struct rdt_resource *r)
> r->cache.min_cbm_bits);
> return false;
> }
> -
> +done:
> *data = val;
> return true;
> }

Isn't it AMD supports 0 minimal CBM bits? Then should set its min_cbm_bits as 0.
Is the following patch a better fix? I don't have AMD machine and cannot
test the patch.

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 6055d05af4cc..031d77dd982d 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -909,6 +909,7 @@ 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;