Messages in this thread | | | Date | Tue, 17 May 2022 09:49:22 -0700 | Subject | Re: [PATCH v2] x86/resctrl: Fix zero cbm for AMD in cbm_validate | From | Reinette Chatre <> |
| |
Hi Fenghua,
On 5/17/2022 9:33 AM, Fenghua Yu wrote: > 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;
That is actually what Stephane's V1 [1] did and I proposed that he fixes it with (almost) what he has in V2 (I think the check can be moved earlier before any bits are searched for).
The reasons why I proposed this change are: - min_cbm_bits is a value that is exposed to user space and from the time AMD was supported this has always been 1 for those systems. I do not know how user space uses this value and unless I can be certain making this 0 will not affect user space I would prefer not to make such a change.
- this fix restores original behavior that was changed in the patch noted in the Fixes link.
- this fix itself relies on math on error returns of bit checking on an empty bitmap. I find that hides what the code does and this fix is more obvious. You can see this feedback in my response to V1.
- a fix like the above snippet is incomplete. To be appropriate the initialization of rdt_resources_all[] needs to be changed to not initialize min_cbm_bits anymore and move the platform specific bits to rdt_init_res_defs_amd() and rdt_init_res_defs_intel() respectively.
Reinette
[1] https://lore.kernel.org/lkml/20220516055055.2734840-1-eranian@google.com/
| |