Re: [PATCH] Call xen_cleanhighmap() with 4MB aligned for page tables mapping

[Juergen Gross]

On 27/09/17 05:03, 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.
> 
> References: https://lists.xen.org/archives/html/xen-devel/2012-07/msg01562.html
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
> ---
>  arch/x86/xen/mmu_pv.c |   12 +++---------
>  1 files changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
> index 7330cb3..3628d97 100644
> --- a/arch/x86/xen/mmu_pv.c
> +++ b/arch/x86/xen/mmu_pv.c
> @@ -1238,21 +1238,15 @@ static void __init xen_pagetable_cleanhighmap(void)
>  	 * from _brk_limit way up to the max_pfn_mapped (which is the end of
>  	 * the ramdisk). We continue on, erasing PMD entries that point to page
>  	 * tables - do note that they are accessible at this stage via __va.
> -	 * For good measure we also round up to the PMD - which means that if
> +	 * For good measure we also round up to the PMD*2 - which means that if

Could you please add in the comment that Xen is aligning the memory end
to a 4MB boundary?

>  	 * anybody is using __ka address to the initial boot-stack - and try
>  	 * to use it - they are going to crash. The xen_start_info has been
>  	 * taken care of already in xen_setup_kernel_pagetable. */
>  	addr = xen_start_info->pt_base;
> -	size = roundup(xen_start_info->nr_pt_frames * PAGE_SIZE, PMD_SIZE);
> +	size = xen_start_info->nr_pt_frames * PAGE_SIZE;
>  
> -	xen_cleanhighmap(addr, addr + size);
> +	xen_cleanhighmap(addr, roundup(addr + size, PMD_SIZE*2));

Coding style: please use "PMD_SIZE * 2".


Juergen