Re: [Xen-devel] [PATCH] xen: arm: force guest memory accesses to cacheable when MMU is disabled

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 8 Jan 2014, Ian Campbell wrote:
> On Tue, 2014-01-07 at 20:39 +0000, Stefano Stabellini wrote:
> > > diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> > > index 124cccf..104d228 100644
> > > --- a/xen/arch/arm/domain.c
> > > +++ b/xen/arch/arm/domain.c
> > > @@ -219,6 +219,11 @@ static void ctxt_switch_to(struct vcpu *n)
> > >      else
> > >          hcr |= HCR_RW;
> > >  
> > > +    if ( n->arch.sctlr & SCTLR_M )
> > > +        hcr &= ~(HCR_TVM|HCR_DC);
> > > +    else
> > > +        hcr |= (HCR_TVM|HCR_DC);
> > > +
> > >      WRITE_SYSREG(hcr, HCR_EL2);
> > >      isb();
> > 
> > Is this actually needed? Shouldn't HCR be already correctly updated by
> > update_sctlr?
> 
> Not if we are switching back and forth between two guests which are in
> different states.

I didn't realize that HCR is not properly saved and restored during
context switch. Maybe it is worth doing that instead? If nothing else
for simplicity?

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