Re: Stupid Xen vs KVM question

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Dec 04, 2014 at 02:59:48PM -0800, Andy Lutomirski wrote:
> This code in arch/x86/kernel/entry_32.S is wrong:
> 
> #ifdef CONFIG_PARAVIRT
>     /*
>      * The kernel can't run on a non-flat stack if paravirt mode
>      * is active.  Rather than try to fixup the high bits of
>      * ESP, bypass this code entirely.  This may break DOSemu
>      * and/or Wine support in a paravirt VM, although the option
>      * is still available to implement the setting of the high
>      * 16-bits in the INTERRUPT_RETURN paravirt-op.
>      */
>     cmpl $0, pv_info+PARAVIRT_enabled
>     jne restore_nocheck
> #endif
> 
> On KVM guests, it notices that paravirt is enabled and bails.  It
> should work fine on KVM -- the condition it should be checking is
> whether we have native segmentation.
> 
> Do you know the right way to ask that?

We could do a simple thing - which is that the paravirt_enabled
could have the value 1 for Xen and 2 for KVM. The assembler logic
would be inverted and just check for 1. I am not going to attempt
to write the assembler code :-)

> 
> Thanks,
> Andy
> 
> -- 
> Andy Lutomirski
> AMA Capital Management, LLC