Applying a patch on v3.2 to expose the CMPXCHG16B setting

Discussions related to using the OSE version of VirtualBox.

Applying a patch on v3.2 to expose the CMPXCHG16B setting

Postby wodny » 8. Aug 2014, 13:45

Hi,
is it safe to apply a patch from changeset 42613 on VirtualBox 3.2? The patch exposes the possibility of enabling CMPXCHG16B instruction availability flag via a CPUM setting. I don't know if any others changes introduced between 3.2 and 4.2 are required to legally enable this feature. I would like to be able to run a Windows 2012 virtual machine on VirtualBox 3.2 available on Debian Squeeze. As far as I can see in the source code, officially this feature has been introduced in version 4.2 and is discussed in ticket 11899.

I would paste links, but as a new user I cannot post URLs :/
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Re: Applying a patch on v3.2 to expose the CMPXCHG16B settin

Postby Technologov » 7. Oct 2014, 21:07

Just drop patch here, so maybe we can test it together.
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Re: Applying a patch on v3.2 to expose the CMPXCHG16B settin

Postby frank » 9. Oct 2014, 09:28

Actually I see no reason to add this functionality to this old VBox version. VBox 3.2 has only limited support.
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Re: Applying a patch on v3.2 to expose the CMPXCHG16B settin

Postby wodny » 9. Oct 2014, 17:13

Frank Mehnert wrote:Actually I see no reason to add this functionality to this old VBox version. VBox 3.2 has only limited support.


As I have written -- because of having Debian Squeeze. Even after installing a backported version it will be at most 4.0.10. Versions higher than 4.2 are available from wheezy-backports up.
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Re: Applying a patch on v3.2 to expose the CMPXCHG16B settin

Postby Perryg » 9. Oct 2014, 17:29

All of this discussion indicates that you are using the Debian (fork) of VirtualBox and not the official release from virtualbox.org. If you are wanting support for that version you should ask the Debian maintainer what should be done. As for the official release you simply update the version to what you need to support the guest/s you want to run if need be.
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Re: Applying a patch on v3.2 to expose the CMPXCHG16B settin

Postby Technologov » 9. Oct 2014, 19:34

Perhaps, because this is a new feature, you may use a newer backport, or official Oracle release.
Changing Debian package is only for bugfix
But if Debian VBox maintainers agree to push new patches, I may be available to test.
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Re: Applying a patch on v3.2 to expose the CMPXCHG16B settin

Postby wodny » 9. Oct 2014, 22:20

Technologov wrote:Perhaps, because this is a new feature, you may use a newer backport, or official Oracle release.
Changing Debian package is only for bugfix
But if Debian VBox maintainers agree to push new patches, I may be available to test.


I could test it myself I suppose. I was just interested if spending time on patching and recompiling has sense. I was interested in knowing if this problem is just about enabling/disabling a flag or some other code has to manage somehow this change. For example: with this flag enabled a module of VirtualBox has to recompile machine code differently on the fly... Testing for regressions in this case would be very hard. For example you could do fine until some code depending on that instruction kicks in.
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