Re: [Xen-devel] Linux'es free_initmem() on Xen

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.02.16 at 16:09, <david.vrabel@xxxxxxxxxx> wrote:
> On 02/02/16 14:10, Jan Beulich wrote:
>>>>> On 02.02.16 at 14:30, <david.vrabel@xxxxxxxxxx> wrote:
>>> On 02/02/16 12:44, Jan Beulich wrote:
>>>> All,
>>>>
>>>> while looking into some of the DEBUG_WX issues I came across
>>>> aforementioned function and started wondering how pv-ops gets
>>>> away without the unmapping XenoLinux has always been doing
>>>> (in free_init_pages()).
>>>
>>> Um.  I'm not sure why you think something needs to be unmapped.  This is
>>> freeing the pages back to the page allocator -- thus the pages still
>>> need to be mapped.
>> 
>> In the 1:1 mapping, yes. But the secondary mapping in the kernel
>> VA range is not needed anymore, and (unless accounted for) would
>> get in the way of said operations.
> 
> The PMDs are shared between the two mappings. See
> xen_setup_kernel_pagetable().

I see. While a neat solution of keeping the two in sync, doesn't
this create a small(?) problem, in that it subverts
change_page_attr_set_clr()'s suppression of the 1:1 map
updating when e.g. a kernel or module va range gets just its NX
bit altered (in particular when the bit gets set)?

Jan


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