Re: [kvm-devel] [PATCH] gfxboot VMX workaround v2

[Anthony Liguori]

Alexander Graf wrote:

On Apr 7, 2008, at 6:05 PM, Anthony Liguori wrote:

Alexander Graf wrote:

Hi,

this is an improved version of the patch I sent several weeks ago to

patches it to work on Intel CPUs on the fly. The big difference is that


Please do _not_ apply this patch. I send it to the list only for
interested people, who would like to have a working version of KVM for
their systems right now. It is neither a proper fix nor the right
approach to deal with this issue. It is merely a hack that works for me
and maybe for others too.

this list. Functionally nothing changed; it still hacks into gfxboot and this version is cleaned up and should work with every future CPU available.

Perhaps a viable way to fix this upstream would be to catch the vmentry failure, look to see if SS.CPL != CS.CPL, and if so, invoke x86_emulate() in a loop until SS.CPL == CS.CPL. There are very few instructions in gfxboot that would need to be added to x86_emulate (if they aren't already there).

In a previous thread Avi already explained a quite reasonable way to approach this problem, which I believe is a really good approach. He wanted to x86_emulate until the environment is "VMX friendly" again, thus resolving big real mode problems as well.

       jmp pm_seg.prog_c32:switch_to_pm_20
switch_to_pm_20:

       bits 32

       mov ax,pm_seg.prog_d16
       mov ds,ax
       mov eax,ss



Regards,

Anthony Liguori

I've got a slightly lamer approach than what Avi probably wants. I lost interest in updating x86_emulate once I realized how far xen's copy has gotten. To get GFXBOOT 3.3.28 working just requires adding far jmp to x86_emulate. The sequence should look like: Which means we'll get 3 vmentry failures. The two moves should already be supported by x86_emulate but I haven't confirmed. It's not a complete solution to our real mode woes but I think it's a reasonable first step.

I personally agree that the real approach is way superior to my patch. I just won't have the time to do it in the near future and not being able to boot intuitively hurts KVM users unnecessarily ;-).

Regards,

Alex

x86_emulate.patch
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