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Subject: Re: [PATCH] pseries/drmem: update LMBs after LPM
To:     Laurent Dufour <ldufour@linux.ibm.com>, mpe@ellerman.id.au,
        benh@kernel.crashing.org, paulus@samba.org
Cc:     nathanl@linux.ibm.com, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org
References: <20210427150113.14368-1-ldufour@linux.ibm.com>
From:   Tyrel Datwyler <tyreld@linux.ibm.com>
Message-ID: <8b36065d-e4b4-bc0c-cf69-f01c91e49061@linux.ibm.com>
Date:   Tue, 27 Apr 2021 10:01:11 -0700
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On 4/27/21 8:01 AM, Laurent Dufour wrote:
> 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.
> 
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> ---
>  arch/powerpc/include/asm/drmem.h          |  1 +
>  arch/powerpc/mm/drmem.c                   | 48 +++++++++++++++++++++++
>  arch/powerpc/platforms/pseries/mobility.c |  9 +++++
>  3 files changed, 58 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/drmem.h b/arch/powerpc/include/asm/drmem.h
> index bf2402fed3e0..55c2c25085b0 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(void);
>  #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..46074bdfdb3c 100644
> --- a/arch/powerpc/mm/drmem.c
> +++ b/arch/powerpc/mm/drmem.c
> @@ -307,6 +307,54 @@ 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(void)
> +{
> +	struct device_node *node;
> +	const __be32 *prop;
> +
> +	node = of_find_node_by_path("/ibm,dynamic-reconfiguration-memory");
> +	if (!node)
> +		return;
> +
> +	prop = of_get_property(node, "ibm,dynamic-memory", NULL);
> +	if (prop) {
> +		__walk_drmem_v1_lmbs(prop, NULL, NULL, update_lmb);
> +	} else {
> +		prop = of_get_property(node, "ibm,dynamic-memory-v2", NULL);
> +		if (prop)
> +			__walk_drmem_v2_lmbs(prop, NULL, NULL, update_lmb);
> +	}
> +
> +	of_node_put(node);
> +}
>  #endif
> 
>  static int init_drmem_lmb_size(struct device_node *dn)
> diff --git a/arch/powerpc/platforms/pseries/mobility.c b/arch/powerpc/platforms/pseries/mobility.c
> index ea4d6a660e0d..c68eccc6e8df 100644
> --- a/arch/powerpc/platforms/pseries/mobility.c
> +++ b/arch/powerpc/platforms/pseries/mobility.c
> @@ -25,6 +25,7 @@
> 
>  #include <asm/machdep.h>
>  #include <asm/rtas.h>
> +#include <asm/drmem.h>
>  #include "pseries.h"
>  #include "../../kernel/cacheinfo.h"
> 
> @@ -237,6 +238,7 @@ int pseries_devicetree_update(s32 scope)
>  	__be32 *data;
>  	int update_nodes_token;
>  	int rc;
> +	bool drmem_updated = false;
> 
>  	update_nodes_token = rtas_token("ibm,update-nodes");
>  	if (update_nodes_token == RTAS_UNKNOWN_SERVICE)
> @@ -271,6 +273,10 @@ int pseries_devicetree_update(s32 scope)
>  					continue;
>  				}
> 
> +				if (!strcmp(np->full_name,
> +					    "ibm,dynamic-reconfiguration-memory"))
> +					drmem_updated = true;

Is there a reason that we can't use the existing pseries_memory_notifier()
callback in pseries/hotplug-memory.c to trigger the drmem_update_lmbs() when
either the ibm,dynamic-memory or ibm,dynamic-memory-v2 properties are updated?

Something like:

static int pseries_memory_notifier(struct notifier_block *nb,
                                   unsigned long action, void *data)
{
        struct of_reconfig_data *rd = data;
        int err = 0;

        switch (action) {
        case OF_RECONFIG_ATTACH_NODE:
                err = pseries_add_mem_node(rd->dn);
                break;
        case OF_RECONFIG_DETACH_NODE:
                err = pseries_remove_mem_node(rd->dn);
                break;
	case OF_RECONFIG_UPDATE_PROPERTY:
		if (!strcmp(rd->dn->full_name, "ibm,dynamic-reconfiguration-memory"));
			drmem_update_lmbs(rd->prop);
		break;
        }
        return notifier_from_errno(err);
}

Your drmem_update_lmbs() would need to be updated to take a property and to
check the property name against ibm,dyanmic-memory[-v2].

-Tyrel

> +
>  				switch (action) {
>  				case DELETE_DT_NODE:
>  					delete_dt_node(np);
> @@ -293,6 +299,9 @@ int pseries_devicetree_update(s32 scope)
>  	} while (rc == 1);
> 
>  	kfree(rtas_buf);
> +
> +	if (drmem_updated)
> +		drmem_update_lmbs();
>  	return rc;
>  }
>