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Subject: Re: [PATCH v2] Call xen_cleanhighmap() with 4MB aligned for page
 tables mapping
To: Zhenzhong Duan <zhenzhong.duan@oracle.com>, mingo@redhat.com,
        boris.ostrovsky@oracle.com, tglx@linutronix.de, hpa@zytor.com
Cc: x86@kernel.org, xen-devel@lists.xenproject.org,
        srinivas.eeda@oracle.com, joe.jin@oracle.com,
        linux-kernel@vger.kernel.org
References: <85bd42d5-b0d2-40f5-81a9-14cb51ec4503@default>
From: Juergen Gross <jgross@suse.com>
Message-ID: <d5d1fd24-ce7d-1e12-6522-e3cb220858a5@suse.com>
Date: Wed, 27 Sep 2017 11:43:42 +0200
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On 27/09/17 11:41, Zhenzhong Duan wrote:
> When bootup a PVM guest with large memory(Ex.240GB), XEN provided initial
> mapping overlaps with kernel module virtual space. When mapping in this space
> is cleared by xen_cleanhighmap(), in certain case there could be an 2MB mapping
> left. This is due to XEN initialize 4MB aligned mapping but xen_cleanhighmap()
> finish at 2MB boundary.
> 
> When module loading is just on top of the 2MB space, got below warning:
> 
> WARNING: at mm/vmalloc.c:106 vmap_pte_range+0x14e/0x190()
> Call Trace:
>  [<ffffffff81117083>] warn_alloc_failed+0xf3/0x160
>  [<ffffffff81146022>] __vmalloc_area_node+0x182/0x1c0
>  [<ffffffff810ac91e>] ? module_alloc_update_bounds+0x1e/0x80
>  [<ffffffff81145df7>] __vmalloc_node_range+0xa7/0x110
>  [<ffffffff810ac91e>] ? module_alloc_update_bounds+0x1e/0x80
>  [<ffffffff8103ca54>] module_alloc+0x64/0x70
>  [<ffffffff810ac91e>] ? module_alloc_update_bounds+0x1e/0x80
>  [<ffffffff810ac91e>] module_alloc_update_bounds+0x1e/0x80
>  [<ffffffff810ac9a7>] move_module+0x27/0x150
>  [<ffffffff810aefa0>] layout_and_allocate+0x120/0x1b0
>  [<ffffffff810af0a8>] load_module+0x78/0x640
>  [<ffffffff811ff90b>] ? security_file_permission+0x8b/0x90
>  [<ffffffff810af6d2>] sys_init_module+0x62/0x1e0
>  [<ffffffff815154c2>] system_call_fastpath+0x16/0x1b
> 
> Then the mapping of 2MB is cleared, finally oops when the page in that space is
> accessed.
> 
> BUG: unable to handle kernel paging request at ffff880022600000
> IP: [<ffffffff81260877>] clear_page_c_e+0x7/0x10
> PGD 1788067 PUD 178c067 PMD 22434067 PTE 0
> Oops: 0002 [#1] SMP
> Call Trace:
>  [<ffffffff81116ef7>] ? prep_new_page+0x127/0x1c0
>  [<ffffffff81117d42>] get_page_from_freelist+0x1e2/0x550
>  [<ffffffff81133010>] ? ii_iovec_copy_to_user+0x90/0x140
>  [<ffffffff81119c9d>] __alloc_pages_nodemask+0x12d/0x230
>  [<ffffffff81155516>] alloc_pages_vma+0xc6/0x1a0
>  [<ffffffff81006ffd>] ? pte_mfn_to_pfn+0x7d/0x100
>  [<ffffffff81134cfb>] do_anonymous_page+0x16b/0x350
>  [<ffffffff81139c34>] handle_pte_fault+0x1e4/0x200
>  [<ffffffff8100712e>] ? xen_pmd_val+0xe/0x10
>  [<ffffffff810052c9>] ? __raw_callee_save_xen_pmd_val+0x11/0x1e
>  [<ffffffff81139dab>] handle_mm_fault+0x15b/0x270
>  [<ffffffff81510c10>] do_page_fault+0x140/0x470
>  [<ffffffff8150d7d5>] page_fault+0x25/0x30
> 
> Call xen_cleanhighmap() with 4MB aligned for page tables mapping to fix it.
> The unnecessory call of xen_cleanhighmap() in DEBUG mode is also removed.
> 
> -v2: add comment about XEN alignment from Juergen.
> 
> References: https://lists.xen.org/archives/html/xen-devel/2012-07/msg01562.html
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen