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Date:   Wed, 6 May 2020 15:55:29 +0200
From:   Pankaj Gupta <pankaj.gupta.linux@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        linux-nvdimm@...ts.01.org, kexec@...ts.infradead.org,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Baoquan He <bhe@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v3 3/3] device-dax: Add memory via add_memory_driver_managed()

> Currently, when adding memory, we create entries in /sys/firmware/memmap/
> as "System RAM". This will lead to kexec-tools to add that memory to the
> fixed-up initial memmap for a kexec kernel (loaded via kexec_load()). The
> memory will be considered initial System RAM by the kexec'd kernel and
> can no longer be reconfigured. This is not what happens during a real
> reboot.
>
> Let's add our memory via add_memory_driver_managed() now, so we won't
> create entries in /sys/firmware/memmap/ and indicate the memory as
> "System RAM (kmem)" in /proc/iomem. This allows everybody (especially
> kexec-tools) to identify that this memory is special and has to be treated
> differently than ordinary (hotplugged) System RAM.
>
> Before configuring the namespace:
>         [root@...alhost ~]# cat /proc/iomem
>         ...
>         140000000-33fffffff : Persistent Memory
>           140000000-33fffffff : namespace0.0
>         3280000000-32ffffffff : PCI Bus 0000:00
>
> After configuring the namespace:
>         [root@...alhost ~]# cat /proc/iomem
>         ...
>         140000000-33fffffff : Persistent Memory
>           140000000-1481fffff : namespace0.0
>           148200000-33fffffff : dax0.0
>         3280000000-32ffffffff : PCI Bus 0000:00
>
> After loading kmem before this change:
>         [root@...alhost ~]# cat /proc/iomem
>         ...
>         140000000-33fffffff : Persistent Memory
>           140000000-1481fffff : namespace0.0
>           150000000-33fffffff : dax0.0
>             150000000-33fffffff : System RAM
>         3280000000-32ffffffff : PCI Bus 0000:00
>
> After loading kmem after this change:
>         [root@...alhost ~]# cat /proc/iomem
>         ...
>         140000000-33fffffff : Persistent Memory
>           140000000-1481fffff : namespace0.0
>           150000000-33fffffff : dax0.0
>             150000000-33fffffff : System RAM (kmem)
>         3280000000-32ffffffff : PCI Bus 0000:00
>
> After a proper reboot:
>         [root@...alhost ~]# cat /proc/iomem
>         ...
>         140000000-33fffffff : Persistent Memory
>           140000000-1481fffff : namespace0.0
>           148200000-33fffffff : dax0.0
>         3280000000-32ffffffff : PCI Bus 0000:00
>
> Within the kexec kernel before this change:
>         [root@...alhost ~]# cat /proc/iomem
>         ...
>         140000000-33fffffff : Persistent Memory
>           140000000-1481fffff : namespace0.0
>           150000000-33fffffff : System RAM
>         3280000000-32ffffffff : PCI Bus 0000:00
>
> Within the kexec kernel after this change:
>         [root@...alhost ~]# cat /proc/iomem
>         ...
>         140000000-33fffffff : Persistent Memory
>           140000000-1481fffff : namespace0.0
>           148200000-33fffffff : dax0.0
>         3280000000-32ffffffff : PCI Bus 0000:00
>
> /sys/firmware/memmap/ before this change:
>         0000000000000000-000000000009fc00 (System RAM)
>         000000000009fc00-00000000000a0000 (Reserved)
>         00000000000f0000-0000000000100000 (Reserved)
>         0000000000100000-00000000bffdf000 (System RAM)
>         00000000bffdf000-00000000c0000000 (Reserved)
>         00000000feffc000-00000000ff000000 (Reserved)
>         00000000fffc0000-0000000100000000 (Reserved)
>         0000000100000000-0000000140000000 (System RAM)
>         0000000150000000-0000000340000000 (System RAM)
>
> /sys/firmware/memmap/ after a proper reboot:
>         0000000000000000-000000000009fc00 (System RAM)
>         000000000009fc00-00000000000a0000 (Reserved)
>         00000000000f0000-0000000000100000 (Reserved)
>         0000000000100000-00000000bffdf000 (System RAM)
>         00000000bffdf000-00000000c0000000 (Reserved)
>         00000000feffc000-00000000ff000000 (Reserved)
>         00000000fffc0000-0000000100000000 (Reserved)
>         0000000100000000-0000000140000000 (System RAM)
>
> /sys/firmware/memmap/ after this change:
>         0000000000000000-000000000009fc00 (System RAM)
>         000000000009fc00-00000000000a0000 (Reserved)
>         00000000000f0000-0000000000100000 (Reserved)
>         0000000000100000-00000000bffdf000 (System RAM)
>         00000000bffdf000-00000000c0000000 (Reserved)
>         00000000feffc000-00000000ff000000 (Reserved)
>         00000000fffc0000-0000000100000000 (Reserved)
>         0000000100000000-0000000140000000 (System RAM)
>
> kexec-tools already seem to basically ignore any System RAM that's not
> on top level when searching for areas to place kexec images - but also
> for determining crash areas to dump via kdump. Changing the resource name
> won't have an impact.
>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@...il.com>
> Cc: Wei Yang <richard.weiyang@...il.com>
> Cc: Baoquan He <bhe@...hat.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Eric Biederman <ebiederm@...ssion.com>
> Cc: Pavel Tatashin <pasha.tatashin@...een.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  drivers/dax/kmem.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 3d0a7e702c94..5a645a24e359 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -65,7 +65,13 @@ int dev_dax_kmem_probe(struct device *dev)
>         new_res->flags = IORESOURCE_SYSTEM_RAM;
>         new_res->name = dev_name(dev);
>
> -       rc = add_memory(numa_node, new_res->start, resource_size(new_res));
> +       /*
> +        * Ensure that future kexec'd kernels will not treat this as RAM
> +        * automatically.
> +        */
> +       rc = add_memory_driver_managed(numa_node, new_res->start,
> +                                      resource_size(new_res),
> +                                      "System RAM (kmem)");
>         if (rc) {
>                 release_resource(new_res);
>                 kfree(new_res);
> --

Acked-by: Pankaj Gupta <pankaj.gupta.linux@...il.com>

> 2.25.3
>

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