Re: [PATCH -V2] cxl/region: Support to calculate memory tier abstract distance
From: Huang, Ying
Date: Mon Jun 17 2024 - 20:30:57 EST
Dave Jiang <dave.jiang@xxxxxxxxx> writes:
> On 6/16/24 7:10 PM, Huang, Ying wrote:
>> Alison Schofield <alison.schofield@xxxxxxxxx> writes:
>>
>>> On Tue, Jun 11, 2024 at 01:54:23PM +0800, Ying Huang wrote:
>>
>> [snip]
>>
>>>> ---
>>>> drivers/cxl/core/region.c | 40 +++++++++++++++++++++++++++++++++++----
>>>> drivers/cxl/cxl.h | 2 ++
>>>> 2 files changed, 38 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>>>> index 3c2b6144be23..81d0910c0a02 100644
>>>> --- a/drivers/cxl/core/region.c
>>>> +++ b/drivers/cxl/core/region.c
>>>> @@ -9,6 +9,7 @@
>>>> #include <linux/uuid.h>
>>>> #include <linux/sort.h>
>>>> #include <linux/idr.h>
>>>> +#include <linux/memory-tiers.h>
>>>> #include <cxlmem.h>
>>>> #include <cxl.h>
>>>> #include "core.h"
>>>> @@ -2304,14 +2305,20 @@ static bool cxl_region_update_coordinates(struct cxl_region *cxlr, int nid)
>>>> return true;
>>>> }
>>>>
>>>> +static int cxl_region_nid(struct cxl_region *cxlr)
>>>> +{
>>>> + struct cxl_region_params *p = &cxlr->params;
>>>> + struct cxl_endpoint_decoder *cxled = p->targets[0];
>>>> + struct cxl_decoder *cxld = &cxled->cxld;
>>>> +
>>>> + return phys_to_target_node(cxld->hpa_range.start);
>>>> +}
>>>> +
>>>
>>> I believe it's OK to send a resource_size_t to phys_to_target_node()
>>> like this:
>>>
>>> --- a/drivers/cxl/core/region.c
>>> +++ b/drivers/cxl/core/region.c
>>> @@ -2308,10 +2308,8 @@ static bool cxl_region_update_coordinates(struct cxl_region *cxlr, int nid)
>>> static int cxl_region_nid(struct cxl_region *cxlr)
>>> {
>>> struct cxl_region_params *p = &cxlr->params;
>>> - struct cxl_endpoint_decoder *cxled = p->targets[0];
>>> - struct cxl_decoder *cxld = &cxled->cxld;
>>>
>>> - return phys_to_target_node(cxld->hpa_range.start);
>>> + return phys_to_target_node(p->res->start);
>>> }
>>>
>>
>> Read the related code again, it appears that there's a theoretical race
>> condition here. The register_memory_notifier() is called in
>> devm_cxl_add_region(), where p->targets[] and p->res haven't been
>> setupped yet. And, IIUC, p->targets[] or p->res may be gone during the
>> life cycle of regions too. If so, we need to use
>> guard(rwsem_read)(&cxl_region_rwsem) to protect p->targets[] and p->res
>> references. Because the memory notifier may be called for other nodes
>> online/offline.
>
> You mind sending a patch? :)
Sure. Will do it.
--
Best Regards,
Huang, Ying