Re: RFC Patch for the "x86-64, mm: Put early page table high"

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 04/29/2011 02:33 PM, Konrad Rzeszutek Wilk wrote:
> On Fri, Apr 29, 2011 at 01:58:33PM -0700, Jeremy Fitzhardinge wrote:
>> On 04/29/2011 08:46 AM, Konrad Rzeszutek Wilk wrote:
>>> Without a fix for this 2.6.39-rc5 fails during bootup.
>>>
>>> It fails such early, you only Xen telling you that the domain crashed.
>>>
>>> There is one patch to fix this, and the last word was here:
>>>  http://marc.info/?i=4DAF0ECB.8060009@goop.org
>>>
>>> But after nothing had been heard from Peter.
>>>
>>> So I decided to look at this from a different perspective: why not
>>> contain the workaround inside Xen early bootup code.
>>>
>>> I've tested this code as DomU (1G, 2G, 3G), Dom0 (8G, 4G, 1000M)
>>> and they all booted fine. Hadn't compile tested it on 32-bit and
>>> I think it will actually complain about it. Let me fix that.
>>>
>>> See attached patch (also present in stable/bug-fixes-for-rc5) which also
>>> has the "xen: mask_rw_pte mark RO all pagetable pages up to pgt_buf_top"
>>> integrated in.
>> Well, if we can hide the fix away in our code, then that has obvious
>> advantages.  But I worry that this change is pretty closely dependent on
>> how the other code works, and would be fragile in the face of further
>> changes to that code (esp since there's no obvious coupling between the
>> two, so anyone changing the arch/x86 code wouldn't have any clues to
>> look at the corresponding Xen code).
> True. I am hoping to remove this in 2.6.40 though...

That makes it more palatable.  What's the solution for 40+?

    J