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Re: [Qemu-devel] [RFC PATCH 1/1] linux-user: Probe the guest base for sh

From: Andreas Färber
Subject: Re: [Qemu-devel] [RFC PATCH 1/1] linux-user: Probe the guest base for shared objects when needed
Date: Wed, 27 Jun 2012 19:53:56 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120421 Thunderbird/12.0

Am 27.06.2012 19:32, schrieb Richard Henderson:
> On 06/27/2012 08:51 AM, Meador Inge wrote:
>> To solve this issue I experimented with performing a similar probing in 
>> 'main'
>> as in 'probe_guest_base' so that we can find a reserved VA region that also
>> passes validation.  If a region isn't found that can be validated, then QEMU
>> gives up.  Does this approach seem reasonable?
> I guess so, depending on how you adjust the hint each time.
> I do wonder if it wouldn't be better to rearrange things such that
> for 64-bit hosts and 32-bit guests we *always* reserve 4G so that
> there's zero possibility of the guest stomping on host memory.  That
> would also solve your problem.

openSUSE uses a version patched so that IIUC 3G are reserved.
Just today this failed on a system where swap got disabled and the
mmap() thus failed.

Alex suggested an algorithm that starts at 3G (4G, whatever) and when
that fails probes lower limits until it succeeds.

Either way, it's not a new problem, and each solution so far has had
other drawbacks... cc'ing the relevant folks.


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