Re: [RFC PATCH] x86_64,entry,xen: Do not invoke espfix64 on Xen

[Boris Ostrovsky]

On 07/15/2014 01:22 PM, Andy Lutomirski wrote:
> On Tue, Jul 15, 2014 at 10:19 AM, Boris Ostrovsky
> <boris.ostrovsky@xxxxxxxxxx> wrote:
> > On 07/15/2014 12:23 PM, Andy Lutomirski wrote:
> > > diff --git a/arch/x86/kernel/paravirt_patch_64.c
> > > b/arch/x86/kernel/paravirt_patch_64.c
> > > index 3f08f34..a1da673 100644
> > > --- a/arch/x86/kernel/paravirt_patch_64.c
> > > +++ b/arch/x86/kernel/paravirt_patch_64.c
> > > @@ -6,7 +6,6 @@ DEF_NATIVE(pv_irq_ops, irq_disable, "cli");
> > >    DEF_NATIVE(pv_irq_ops, irq_enable, "sti");
> > >    DEF_NATIVE(pv_irq_ops, restore_fl, "pushq %rdi; popfq");
> > >    DEF_NATIVE(pv_irq_ops, save_fl, "pushfq; popq %rax");
> > > -DEF_NATIVE(pv_cpu_ops, iret, "iretq");
> > >    DEF_NATIVE(pv_mmu_ops, read_cr2, "movq %cr2, %rax");
> > >    DEF_NATIVE(pv_mmu_ops, read_cr3, "movq %cr3, %rax");
> > >    DEF_NATIVE(pv_mmu_ops, write_cr3, "movq %rdi, %cr3");
> > > @@ -50,7 +49,6 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
> > >                  PATCH_SITE(pv_irq_ops, save_fl);
> > >                  PATCH_SITE(pv_irq_ops, irq_enable);
> > >                  PATCH_SITE(pv_irq_ops, irq_disable);
> > > -               PATCH_SITE(pv_cpu_ops, iret);
> >
> >
> > Does this mean that we are no longer patching IRET with a jump to a
> > hypercall?
> IIUC this means that, on native, we are no longer patching
> INTERRUPT_RETURN with an "iretq" instruction, so INTERRUPT_RETURN will
> remain a "jmp native_iret".  I'm not sure why this patch was there in
> the first place.  On Xen, it should still get patched with the
> hypercall (although someone should verify this).

Right, I missed the fact that this is native_patch.

I did some light testing and it appears to work. Are you targeting this 
for 3.16?

One way or the other we need to disable espfix64 on PV --- I discovered 
that one of Peter's tests crashes the hypervisor.


-boris
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