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From:   "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To:     Laurent Dufour <ldufour@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
Subject: Re: [PATCH v3] pseries/drmem: update LMBs after LPM
In-Reply-To: <20210428094758.28665-1-ldufour@linux.ibm.com>
References: <20210428094758.28665-1-ldufour@linux.ibm.com>
Date:   Thu, 29 Apr 2021 15:57:35 +0530
Message-ID: <87fsz95qso.fsf@linux.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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? 

IIUC, the call back then will update drmem_lmb->aa_index again?

-aneesh