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From:   Jeff Moyer <jmoyer@redhat.com>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     linux-nvdimm@lists.01.org,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        vishal.l.verma@intel.com, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2 2/4] libnvdimm/namespace: Enforce memremap_compat_align()
References: <158155489850.3343782.2687127373754434980.stgit@dwillia2-desk3.amr.corp.intel.com>
        <158155490897.3343782.14216276134794923581.stgit@dwillia2-desk3.amr.corp.intel.com>
Date:   Thu, 13 Feb 2020 16:55:35 -0500
In-Reply-To: <158155490897.3343782.14216276134794923581.stgit@dwillia2-desk3.amr.corp.intel.com>
        (Dan Williams's message of "Wed, 12 Feb 2020 16:48:29 -0800")
Message-ID: <x49k14q5ezs.fsf@segfault.boston.devel.redhat.com>
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Dan Williams <dan.j.williams@intel.com> writes:

> The pmem driver on PowerPC crashes with the following signature when
> instantiating misaligned namespaces that map their capacity via
> memremap_pages().
>
>     BUG: Unable to handle kernel data access at 0xc001000406000000
>     Faulting instruction address: 0xc000000000090790
>     NIP [c000000000090790] arch_add_memory+0xc0/0x130
>     LR [c000000000090744] arch_add_memory+0x74/0x130
>     Call Trace:
>      arch_add_memory+0x74/0x130 (unreliable)
>      memremap_pages+0x74c/0xa30
>      devm_memremap_pages+0x3c/0xa0
>      pmem_attach_disk+0x188/0x770
>      nvdimm_bus_probe+0xd8/0x470
>
> With the assumption that only memremap_pages() has alignment
> constraints, enforce memremap_compat_align() for
> pmem_should_map_pages(), nd_pfn, or nd_dax cases.
>
> Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Cc: Jeff Moyer <jmoyer@redhat.com>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Link: https://lore.kernel.org/r/158041477336.3889308.4581652885008605170.stgit@dwillia2-desk3.amr.corp.intel.com
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/nvdimm/namespace_devs.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/drivers/nvdimm/namespace_devs.c b/drivers/nvdimm/namespace_devs.c
> index 032dc61725ff..aff1f32fdb4f 100644
> --- a/drivers/nvdimm/namespace_devs.c
> +++ b/drivers/nvdimm/namespace_devs.c
> @@ -1739,6 +1739,16 @@ struct nd_namespace_common *nvdimm_namespace_common_probe(struct device *dev)
>  		return ERR_PTR(-ENODEV);
>  	}
>  
> +	if (pmem_should_map_pages(dev) || nd_pfn || nd_dax) {
> +		struct nd_namespace_io *nsio = to_nd_namespace_io(&ndns->dev);
> +		resource_size_t start = nsio->res.start;
> +
> +		if (!IS_ALIGNED(start | size, memremap_compat_align())) {
> +			dev_dbg(&ndns->dev, "misaligned, unable to map\n");
> +			return ERR_PTR(-EOPNOTSUPP);
> +		}
> +	}
> +
>  	if (is_namespace_pmem(&ndns->dev)) {
>  		struct nd_namespace_pmem *nspm;
>  

Actually, I take back my ack.  :) This prevents a previously working
namespace from being successfully probed/setup.  I thought we were only
going to enforce the alignment for a newly created namespace?  This should
only check whether the alignment works for the current platform.

-Jeff