[PATCH 3.13 044/187] x86_64/entry/xen: Do not invoke espfix64 on Xen

[Kamal Mostafa]

On Wed, 2014-09-17 at 12:25 +0100, Ben Hutchings wrote:
> On Mon, 2014-09-15 at 15:07 -0700, Kamal Mostafa wrote:
> > 3.13.11.7 -stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Andy Lutomirski <luto at amacapital.net>
> > 
> > commit 7209a75d2009dbf7745e2fd354abf25c3deb3ca3 upstream.
> > 
> > This moves the espfix64 logic into native_iret.  To make this work,
> > it gets rid of the native patch for INTERRUPT_RETURN:
> > INTERRUPT_RETURN on native kernels is now 'jmp native_iret'.
> > 
> > This changes the 16-bit SS behavior on Xen from OOPSing to leaking
> > some bits of the Xen hypervisor's RSP (I think).
> > 
> > [ hpa: this is a nonzero cost on native, but probably not enough to
> >   measure. Xen needs to fix this in their own code, probably doing
> >   something equivalent to espfix64. ]
> > 
> > Signed-off-by: Andy Lutomirski <luto at amacapital.net>
> > Link: http://lkml.kernel.org/r/7b8f1d8ef6597cb16ae004a43c56980a7de3cf94.1406129132.git.luto@amacapital.net
> > Signed-off-by: H. Peter Anvin <hpa at linux.intel.com>
> > Signed-off-by: Kamal Mostafa <kamal at canonical.com>
> [...]
> 
> There's another fix related to espfix on Xen, commit 8762e5092828
> ("x86/espfix/xen: Fix allocation of pages for paravirt page tables").
> But I'm not sure whether it's actually needed after this.
> 
> Ben.
> 

I have now queued that one up for 3.13.11.7 also.  Thanks yet again,
Ben!

 -Kamal