Re: [Xen-devel] [PATCH v2] arm: xen: foreign mapping PTEs are special.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 9 Dec 2013, Ian Campbell wrote:
> These mappings are in fact special and require special handling in privcmd,
> which already exists. Failure to mark the PTE as special on arm64 causes all
> sorts of bad PTE fun. e.g.
> 
> e.g.:
> 
> BUG: Bad page map in process xl  pte:e0004077b33f53 pmd:4079575003
> page:ffffffbce1a2f328 count:1 mapcount:-1 mapping:          (null) index:0x0
> page flags: 0x4000000000000014(referenced|dirty)
> addr:0000007fb5259000 vm_flags:040644fa anon_vma:          (null) 
> mapping:ffffffc03a6fda58 index:0
> vma->vm_ops->fault: privcmd_fault+0x0/0x38
> vma->vm_file->f_op->mmap: privcmd_mmap+0x0/0x2c
> CPU: 0 PID: 2657 Comm: xl Not tainted 3.12.0+ #102
> Call trace:
> [<ffffffc0000880f8>] dump_backtrace+0x0/0x12c
> [<ffffffc000088238>] show_stack+0x14/0x1c
> [<ffffffc0004b67e0>] dump_stack+0x70/0x90
> [<ffffffc000125690>] print_bad_pte+0x12c/0x1bc
> [<ffffffc0001268f4>] unmap_single_vma+0x4cc/0x700
> [<ffffffc0001273b4>] unmap_vmas+0x68/0xb4
> [<ffffffc00012c050>] unmap_region+0xcc/0x1d4
> [<ffffffc00012df20>] do_munmap+0x218/0x314
> [<ffffffc00012e060>] vm_munmap+0x44/0x64
> [<ffffffc00012ed78>] SyS_munmap+0x24/0x34
> 
> Where unmap_single_vma contains inlined -> unmap_page_range -> zap_pud_range
> -> zap_pmd_range -> zap_pte_range -> print_bad_pte.
> 
> Or:
> 
> BUG: Bad page state in process xl  pfn:4077b4d
> page:ffffffbce1a2f8d8 count:0 mapcount:-1 mapping:          (null) index:0x0
> page flags: 0x4000000000000014(referenced|dirty)
> Modules linked in:
> CPU: 0 PID: 2657 Comm: xl Tainted: G    B        3.12.0+ #102
> Call trace:
> [<ffffffc0000880f8>] dump_backtrace+0x0/0x12c
> [<ffffffc000088238>] show_stack+0x14/0x1c
> [<ffffffc0004b67e0>] dump_stack+0x70/0x90
> [<ffffffc00010f798>] bad_page+0xc4/0x110
> [<ffffffc00010f8b4>] free_pages_prepare+0xd0/0xd8
> [<ffffffc000110e94>] free_hot_cold_page+0x28/0x178
> [<ffffffc000111460>] free_hot_cold_page_list+0x38/0x60
> [<ffffffc000114cf0>] release_pages+0x190/0x1dc
> [<ffffffc00012c0e0>] unmap_region+0x15c/0x1d4
> [<ffffffc00012df20>] do_munmap+0x218/0x314
> [<ffffffc00012e060>] vm_munmap+0x44/0x64
> [<ffffffc00012ed78>] SyS_munmap+0x24/0x34
> 
> x86 already gets this correct. 32-bit arm gets away with this because there is
> not PTE_SPECIAL bit in the PTE there and the vm_normal_page fallback path does
> the right thing.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> ---
> v2: Expanded commit message.

Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


>  arch/arm/xen/enlighten.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 83e4f95..932cc50 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -96,7 +96,7 @@ static int remap_pte_fn(pte_t *ptep, pgtable_t token, 
> unsigned long addr,
>       struct remap_data *info = data;
>       struct page *page = info->pages[info->index++];
>       unsigned long pfn = page_to_pfn(page);
> -     pte_t pte = pfn_pte(pfn, info->prot);
> +     pte_t pte = pte_mkspecial(pfn_pte(pfn, info->prot));
>  
>       if (map_foreign_page(pfn, info->fgmfn, info->domid))
>               return -EFAULT;
> -- 
> 1.7.10.4
> 

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