Re: [Xen-devel] [PATCH 5/8] kexec: extend hypercall with improved load/unload ops

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Mon, Mar 11, 2013 at 01:43:02PM +0000, David Vrabel wrote:
> On 11/03/13 13:30, Daniel Kiper wrote:
> > On Mon, Mar 11, 2013 at 01:21:30PM +0000, David Vrabel wrote:
> >> On 11/03/13 11:17, Daniel Kiper wrote:
> >>>
> >>> Heh... It looks that there is a misunderstanding. At first I thought
> >>> that David was going to replace purgatory functionality by switching
> >>> from 64-bit to 32-bit in kexec_reloc. But later I realized that
> >>> I missed Xen 64-bit/dom 32-bit case. Now I agree that this switch
> >>> must stay as is. However, now I think that there is another
> >>> small mistake which should be fixed. Please look above.
> >>
> >> Which mistake?  I'm not sure what you're referring to.
> >
> > I thought about that:
> >
> > if ( image->arch == EM_386 )
> >   reloc_flags |= KEXEC_RELOC_FLAG_COMPAT;
> >
> > It should be change to:
> >
> > if ( is_pv_32on64_domain(dom0) )
> >   reloc_flags |= KEXEC_RELOC_FLAG_COMPAT;
>
> This isn't a mistake but a deliberate improvement to the old interface.

I am still not convinced.

> It is clearer and more useful for this sub-architecture to be explicitly
> supplied in the kexec_load call than implicitly through some other
> side-channel.

First of all you do not need to pass any info about architecure to
new kernel or something like that (please check my previous emails).
If any then there is another questions. What do you do if you need
second or third argument?. You redefine kexec interface once again.
For what? Additionally, currently there are a lot of stuff passed
to new kernel via purgatory. And purgatory is called by your
interface too...

> If we go with what you suggest then you prevent kexec from being used
> by: a) PVH dom0s; b) suitably privileged service domains; c) 32-bit

Maybe for PVH should be different check. However,
until now we do not have it in Xen yet.

> guests wanting to load an image with a 64-bit entry point; and d)

Once again:

old_kernel (Xen) -> purgatory (native mode) -> new_kernel

purgatory architecture is same as kexec-tools architecture. If you
use dom0 i386 it means that kexec-tools is (and must be) i386 too.
We do not support Xen i386 anymore. It means that my condition is
correct.

Daniel

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