Re: [PATCH v2 2/5] KVM: arm64: Restore the stage-2 context in VHE's __tlb_switch_to_host()

[Oliver Upton <oliver.upton@linux.dev>]

On Wed, Oct 18, 2023 at 03:00:42PM +0800, Zenghui Yu wrote:
> On 2023/10/13 4:54, Oliver Upton wrote:
> > From: Marc Zyngier <maz@kernel.org>
> > 
> > An MMU notifier could cause us to clobber the stage-2 context loaded on
> > a CPU when we switch to another VM's context to invalidate. This isn't
> > an issue right now as the stage-2 context gets reloaded on every guest
> > entry, but is disastrous when moving __load_stage2() into the
> > vcpu_load() path.
> > 
> > Restore the previous stage-2 context on the way out of a TLB
> > invalidation if we installed something else. Deliberately do this after
> > TGE=1 is synchronized to keep things safe in light of the speculative AT
> > errata.
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> > ---
> >  arch/arm64/kvm/hyp/vhe/tlb.c | 17 ++++++++++++++---
> >  1 file changed, 14 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/arm64/kvm/hyp/vhe/tlb.c b/arch/arm64/kvm/hyp/vhe/tlb.c
> > index f3f2e142e4f4..ef21153ce5fa 100644
> > --- a/arch/arm64/kvm/hyp/vhe/tlb.c
> > +++ b/arch/arm64/kvm/hyp/vhe/tlb.c
> > @@ -11,18 +11,25 @@
> >  #include <asm/tlbflush.h>
> >  struct tlb_inv_context {
> > -	unsigned long	flags;
> > -	u64		tcr;
> > -	u64		sctlr;
> > +	struct kvm_s2_mmu	*mmu;
> > +	unsigned long		flags;
> > +	u64			tcr;
> > +	u64			sctlr;
> >  };
> >  static void __tlb_switch_to_guest(struct kvm_s2_mmu *mmu,
> >  				  struct tlb_inv_context *cxt)
> >  {
> > +	struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
> >  	u64 val;
> >  	local_irq_save(cxt->flags);
> > +	if (vcpu && mmu != vcpu->arch.hw_mmu)
> > +		cxt->mmu = mmu;
> 
> Shouldn't this be
> 
> cxt->mm = vcpu->arch.hw_mmu (the "previous" S2 context)?

It absolutely should, and Marc had it right the first time.

-- 
Thanks,
Oliver