[PATCH 1/2] libnvdimm/altmap: Track namespace boundaries in altmap

[Dan Williams]

On Mon, Sep 9, 2019 at 11:29 PM Aneesh Kumar K.V
<aneesh.kumar at linux.ibm.com> wrote:
>
> With PFN_MODE_PMEM namespace, the memmap area is allocated from the device
> area. Some architectures map the memmap area with large page size. On
> architectures like ppc64, 16MB page for memap mapping can map 262144 pfns.
> This maps a namespace size of 16G.
>
> When populating memmap region with 16MB page from the device area,
> make sure the allocated space is not used to map resources outside this
> namespace. Such usage of device area will prevent a namespace destroy.
>
> Add resource end pnf in altmap and use that to check if the memmap area
> allocation can map pfn outside the namespace. On ppc64 in such case we fallback
> to allocation from memory.
>
> This fix kernel crash reported below:
>
> [  132.034989] WARNING: CPU: 13 PID: 13719 at mm/memremap.c:133 devm_memremap_pages_release+0x2d8/0x2e0
> [  133.464754] BUG: Unable to handle kernel data access at 0xc00c00010b204000
> [  133.464760] Faulting instruction address: 0xc00000000007580c
> [  133.464766] Oops: Kernel access of bad area, sig: 11 [#1]
> [  133.464771] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
> .....
> [  133.464901] NIP [c00000000007580c] vmemmap_free+0x2ac/0x3d0
> [  133.464906] LR [c0000000000757f8] vmemmap_free+0x298/0x3d0
> [  133.464910] Call Trace:
> [  133.464914] [c000007cbfd0f7b0] [c0000000000757f8] vmemmap_free+0x298/0x3d0 (unreliable)
> [  133.464921] [c000007cbfd0f8d0] [c000000000370a44] section_deactivate+0x1a4/0x240
> [  133.464928] [c000007cbfd0f980] [c000000000386270] __remove_pages+0x3a0/0x590
> [  133.464935] [c000007cbfd0fa50] [c000000000074158] arch_remove_memory+0x88/0x160
> [  133.464942] [c000007cbfd0fae0] [c0000000003be8c0] devm_memremap_pages_release+0x150/0x2e0
> [  133.464949] [c000007cbfd0fb70] [c000000000738ea0] devm_action_release+0x30/0x50
> [  133.464955] [c000007cbfd0fb90] [c00000000073a5a4] release_nodes+0x344/0x400
> [  133.464961] [c000007cbfd0fc40] [c00000000073378c] device_release_driver_internal+0x15c/0x250
> [  133.464968] [c000007cbfd0fc80] [c00000000072fd14] unbind_store+0x104/0x110
> [  133.464973] [c000007cbfd0fcd0] [c00000000072ee24] drv_attr_store+0x44/0x70
> [  133.464981] [c000007cbfd0fcf0] [c0000000004a32bc] sysfs_kf_write+0x6c/0xa0
> [  133.464987] [c000007cbfd0fd10] [c0000000004a1dfc] kernfs_fop_write+0x17c/0x250
> [  133.464993] [c000007cbfd0fd60] [c0000000003c348c] __vfs_write+0x3c/0x70
> [  133.464999] [c000007cbfd0fd80] [c0000000003c75d0] vfs_write+0xd0/0x250

Question, does this crash only happen when the namespace is not 16MB
aligned? In other words was this bug exposed by the subsection-hotplug
changes and should it contain Fixes: tag for those commits?