[Qemu-devel] Re: [PATCH v2 16/17] kvm: x86: Rework identity map and TSS setup for larger BIOS sizes

[Avi Kivity]

On 01/03/2011 06:52 PM, Jan Kiszka wrote:
> Am 03.01.2011 17:06, Avi Kivity wrote:
> >  On 01/03/2011 10:33 AM, Jan Kiszka wrote:
> >>  From: Jan Kiszka<address@hidden>
> >>
> >>  First of all, we only need this EPT identity and TSS reservation on
> >>  Intel CPUs.
> >
> >  kvm-amd will ignore it just fine.  I'd like to keep arch differences
> >  away from userspace.
>
> And I would prefer to avoid needlessly cluttering the physical guest
> address space where not needed. Long term, we could even give user space
> a hint (unless it can test it directly) that this workaround is no
> longer needed as the host Intel CPU supports true real mode.

Having different physical address spaces based on the host cpu is bad, 
even disregarding live migration.  If there's a real need, we can do it 
as an option.  I don't see such a need though.

We can definitely add a new KVM_CAP for "tss/ept identity supported but 
not needed".  If emulate_invalid_guest_state is eventually fully 
implemented and becomes the default, it will even be true across the board.

> >
> >>  Then, in order to support loading BIOSes>   256K, reorder the
> >>  code, adjusting the base if the kernel supports moving the identity map.
> >>  We can drop the check for KVM_CAP_SET_TSS_ADDR as we already depend on
> >>  much newer features.
> >
> >  There is no ordering on kvm features.  Each can come and go as it pleases.
> >
>
> Well, at least this is not how kvm upstream works so far.

Let's change it then.

--
error compiling committee.c: too many arguments to function