Re: [Xen-devel] [PATCH] Don't clear HCR_VM bit when updating VTTBR.

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 31 Oct 2016, Steve Capper wrote:
> On Wed, Oct 19, 2016 at 12:59:45PM -0700, Stefano Stabellini wrote:
> > On Mon, 10 Oct 2016, Jun Sun wrote:
> > > Currently function p2m_restore_state() would clear HCR_VM bit, i.e.,
> > > disabling stage2 translation, before updating VTTBR register. After
> > > some research and talking to ARM support, I got confirmed that this is not
> > > necessary. We are currently working on a new platform that would need this
> > > to be removed.
> > > 
> > > The patch is tested on FVP foundation model.
> > > 
> > > Signed-off-by: Jun Sun <jsun@xxxxxxxxxx>
> > 
> > Hello Jun,
> > 
> > thanks for the patch and sorry for the late reply. I would appreciate
> > feedback from Julien, but he is current AFK.
> > 
> > Steve,
> > can I have your Acked-by on this patch?
> > 
> 
> Apologies for my very late reply on this.
> 
> I've taken a look and I think that this is okay, so please feel free to
> add:
> Acked-by: Steve Capper <steve.capper@xxxxxxxxxx>

Thanks Steve. Given the state of the release, I am going to push the fix
to Xen 4.9 unless you or Jun have a strong argument for committing this
sooner.


> > 
> > >  xen/arch/arm/p2m.c | 2 --
> > >  1 file changed, 2 deletions(-)
> > > 
> > > diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> > > index cc5634b..e4991df 100644
> > > --- a/xen/arch/arm/p2m.c
> > > +++ b/xen/arch/arm/p2m.c
> > > @@ -140,8 +140,6 @@ void p2m_restore_state(struct vcpu *n)
> > >          return;
> > >  
> > >      hcr = READ_SYSREG(HCR_EL2);
> > > -    WRITE_SYSREG(hcr & ~HCR_VM, HCR_EL2);
> > > -    isb();
> > >  
> > >      WRITE_SYSREG64(p2m->vttbr, VTTBR_EL2);
> > >      isb();
> > > -- 
> > > 2.7.4
> > > 
> 

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