Re: [Xen-devel] [PATCH] x86-64 linux: unmap temporary mappings established for setup of 1:1 mappings

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> 01.06.06 20:21 >>>
>
>On 31 May 2006, at 14:17, Jan Beulich wrote:
>
>> The temporary mappings needed to set up the 1:1 mappings must be torn 
>> down after use; otherwise they may trigger the
>> WARN_ON() in vmap_pte_range() (namely if the chunk allocated to hold 
>> kernel and initial page tables gets close to or
>> exceeds 128Mb, or if a sufficiently high mem= argument causes the 
>> static allocations to grow beyond 128Mb, which in
>> either case means these mappings extend into the modules area).
>
>I've applied this to -unstable, but in this patch I only see code to 
>destroy the extended init mappings. What happens if you have a really 
>big initrd (for example)? That will push the initial pagetables up into 
>the modules area -- is that handled correctly now or is more fixup 
>required?

The initrd mappings, as I read it, get destroyed in setup_arch(). The thing 
that also came to my mind were the
Xen-created page tables, which might need taking care of. The main issue here 
will be to precisely determine the
boundary of where to start destruction - does Xen make any guarantees regarding 
the ordering of things within the
initial allocation?

>Also your patch didn't apply to 3.0-testing. You'll need to supply a 
>version specifically for -testing if you want it applied there.

Yes, that patch would look different. As we have our own patch anyway, I don't 
think we insist on this being applied to
3.0-testing, but in case you want it I'm attaching the patch we have (one of 
its hunks applies with fuzz 1 only, but I
think that should be okay).

Jan

Attachment: xen-x86_64-unmap-early.patch
Description: Text document

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