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Subject: Re: [PATCH v3] pseries/drmem: update LMBs after LPM
From:   Laurent Dufour <ldufour@linux.ibm.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org
Cc:     nathanl@linux.ibm.com, Tyrel Datwyler <tyreld@linux.ibm.com>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
References: <20210428094758.28665-1-ldufour@linux.ibm.com>
 <87fsz95qso.fsf@linux.ibm.com>
 <e3fcd8b6-6d43-85ed-7036-42430aad4979@linux.ibm.com>
Message-ID: <66c1b88f-6614-52b1-9b53-5fe60a1a813b@linux.ibm.com>
Date:   Thu, 29 Apr 2021 13:35:30 +0200
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Le 29/04/2021 à 13:31, Laurent Dufour a écrit :
> Le 29/04/2021 à 12:27, Aneesh Kumar K.V a écrit :
>> Laurent Dufour <ldufour@linux.ibm.com> writes:
>>
>>> After a LPM, the device tree node ibm,dynamic-reconfiguration-memory may be
>>> updated by the hypervisor in the case the NUMA topology of the LPAR's
>>> memory is updated.
>>>
>>> This is caught by the kernel, but the memory's node is updated because
>>> there is no way to move a memory block between nodes.
>>>
>>> If later a memory block is added or removed, drmem_update_dt() is called
>>> and it is overwriting the DT node to match the added or removed LMB. But
>>> the LMB's associativity node has not been updated after the DT node update
>>> and thus the node is overwritten by the Linux's topology instead of the
>>> hypervisor one.
>>>
>>> Introduce a hook called when the ibm,dynamic-reconfiguration-memory node is
>>> updated to force an update of the LMB's associativity.
>>>
>>> Cc: Tyrel Datwyler <tyreld@linux.ibm.com>
>>> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
>>> ---
>>>
>>> V3:
>>>   - Check rd->dn->name instead of rd->dn->full_name
>>> V2:
>>>   - Take Tyrel's idea to rely on OF_RECONFIG_UPDATE_PROPERTY instead of
>>>   introducing a new hook mechanism.
>>> ---
>>>   arch/powerpc/include/asm/drmem.h              |  1 +
>>>   arch/powerpc/mm/drmem.c                       | 35 +++++++++++++++++++
>>>   .../platforms/pseries/hotplug-memory.c        |  4 +++
>>>   3 files changed, 40 insertions(+)
>>>
>>> diff --git a/arch/powerpc/include/asm/drmem.h b/arch/powerpc/include/asm/drmem.h
>>> index bf2402fed3e0..4265d5e95c2c 100644
>>> --- a/arch/powerpc/include/asm/drmem.h
>>> +++ b/arch/powerpc/include/asm/drmem.h
>>> @@ -111,6 +111,7 @@ int drmem_update_dt(void);
>>>   int __init
>>>   walk_drmem_lmbs_early(unsigned long node, void *data,
>>>                 int (*func)(struct drmem_lmb *, const __be32 **, void *));
>>> +void drmem_update_lmbs(struct property *prop);
>>>   #endif
>>>   static inline void invalidate_lmb_associativity_index(struct drmem_lmb *lmb)
>>> diff --git a/arch/powerpc/mm/drmem.c b/arch/powerpc/mm/drmem.c
>>> index 9af3832c9d8d..f0a6633132af 100644
>>> --- a/arch/powerpc/mm/drmem.c
>>> +++ b/arch/powerpc/mm/drmem.c
>>> @@ -307,6 +307,41 @@ int __init walk_drmem_lmbs_early(unsigned long node, 
>>> void *data,
>>>       return ret;
>>>   }
>>> +/*
>>> + * Update the LMB associativity index.
>>> + */
>>> +static int update_lmb(struct drmem_lmb *updated_lmb,
>>> +              __maybe_unused const __be32 **usm,
>>> +              __maybe_unused void *data)
>>> +{
>>> +    struct drmem_lmb *lmb;
>>> +
>>> +    /*
>>> +     * Brut force there may be better way to fetch the LMB
>>> +     */
>>> +    for_each_drmem_lmb(lmb) {
>>> +        if (lmb->drc_index != updated_lmb->drc_index)
>>> +            continue;
>>> +
>>> +        lmb->aa_index = updated_lmb->aa_index;
>>> +        break;
>>> +    }
>>> +    return 0;
>>> +}
>>> +
>>> +/*
>>> + * Update the LMB associativity index.
>>> + *
>>> + * This needs to be called when the hypervisor is updating the
>>> + * dynamic-reconfiguration-memory node property.
>>> + */
>>> +void drmem_update_lmbs(struct property *prop)
>>> +{
>>> +    if (!strcmp(prop->name, "ibm,dynamic-memory"))
>>> +        __walk_drmem_v1_lmbs(prop->value, NULL, NULL, update_lmb);
>>> +    else if (!strcmp(prop->name, "ibm,dynamic-memory-v2"))
>>> +        __walk_drmem_v2_lmbs(prop->value, NULL, NULL, update_lmb);
>>> +}
>>>   #endif
>>>   static int init_drmem_lmb_size(struct device_node *dn)
>>> diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c 
>>> b/arch/powerpc/platforms/pseries/hotplug-memory.c
>>> index 8377f1f7c78e..672ffbee2e78 100644
>>> --- a/arch/powerpc/platforms/pseries/hotplug-memory.c
>>> +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
>>> @@ -949,6 +949,10 @@ static int pseries_memory_notifier(struct notifier_block 
>>> *nb,
>>>       case OF_RECONFIG_DETACH_NODE:
>>>           err = pseries_remove_mem_node(rd->dn);
>>>           break;
>>> +    case OF_RECONFIG_UPDATE_PROPERTY:
>>> +        if (!strcmp(rd->dn->name,
>>> +                "ibm,dynamic-reconfiguration-memory"))
>>> +            drmem_update_lmbs(rd->prop);
>>>       }
>>>       return notifier_from_errno(err);
>>
>> How will this interact with DLPAR memory? When we dlpar memory,
>> ibm,configure-connector is used to fetch the new associativity details
>> and set drmem_lmb->aa_index correctly there. Once that is done kernel
>> then call drmem_update_dt() which will result in the above notifier
>> callback?
> 
> When a memory DLPAR operation is done, the in memory DT property 
> "ibm,dynamic-memory" or "ibm,dynamic-memory-v2" (if existing) have to be updated 
> to reflect the added/removed memory part. This is done by calling 
> drmem_update_dt().
> 
> This patch is addressing the case where the hypervisor has updated the DT 
> property mentioned above. In that case, the LMB tree should be updated so the 
> aa_index fields are matching the DT one. This way the next time a memory DLPAR 
> operation is done the DT properties "ibm,dynamic-memory" or 
> "ibm,dynamic-memory-v2" will be rebuilt correctly.
> 
>> IIUC, the call back then will update drmem_lmb->aa_index again?

Oh I missed what you pointed out.
Please ignore my previous answer, I need to double check code.

> drmem_update_dt() is not updating drmem_lmb->aa_index, that's the oppposite, it 
> is rebuilding the in memory DT property "ibm,dynamic-memory" or 
> "ibm,dynamic-memory-v2" based on the data stored in the LMB tree.
> 
> Laurent.