Re: [PATCH] KVM: arm64: Fix unaligned addr case in mmu walking

[Marc Zyngier]

On 2021-03-04 00:46, Justin He wrote:
> Hi Marc
>
> > -----Original Message-----
> > From: Will Deacon <will@xxxxxxxxxx>
> > Sent: Thursday, March 4, 2021 5:13 AM
> > To: Marc Zyngier <maz@xxxxxxxxxx>
> > Cc: Justin He <Justin.He@xxxxxxx>; kvmarm@xxxxxxxxxxxxxxxxxxxxx; James
> > Morse <James.Morse@xxxxxxx>; Julien Thierry 
> > <julien.thierry.kdev@xxxxxxxxx>;
> > Suzuki Poulose <Suzuki.Poulose@xxxxxxx>; Catalin Marinas
> > <Catalin.Marinas@xxxxxxx>; Gavin Shan <gshan@xxxxxxxxxx>; Yanan Wang
> > <wangyanan55@xxxxxxxxxx>; Quentin Perret <qperret@xxxxxxxxxx>; 
> > linux-arm-
> > kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH] KVM: arm64: Fix unaligned addr case in mmu 
> > walking
> >
> > On Wed, Mar 03, 2021 at 07:07:37PM +0000, Marc Zyngier wrote:
> > > From e0524b41a71e0f17d6dc8f197e421e677d584e72 Mon Sep 17 00:00:00 2001
> > > From: Jia He <justin.he@xxxxxxx>
> > > Date: Wed, 3 Mar 2021 10:42:25 +0800
> > > Subject: [PATCH] KVM: arm64: Fix range alignment when walking page tables
> > >
> > > When walking the page tables at a given level, and if the start
> > > address for the range isn't aligned for that level, we propagate
> > > the misalignment on each iteration at that level.
> > >
> > > This results in the walker ignoring a number of entries (depending
> > > on the original misalignment) on each subsequent iteration.
> > >
> > > Properly aligning the address at the before the next iteration
> >
> > "at the before the next" ???
> >
> > > addresses the issue.
> > >
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Reported-by: Howard Zhang <Howard.Zhang@xxxxxxx>
> > > Signed-off-by: Jia He <justin.he@xxxxxxx>
> > > Fixes: b1e57de62cfb ("KVM: arm64: Add stand-alone page-table walker
> > infrastructure")
> > > [maz: rewrite commit message]
> > > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> > > Link: https://lore.kernel.org/r/20210303024225.2591-1-justin.he@xxxxxxx
> > > ---
> > >  arch/arm64/kvm/hyp/pgtable.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> > > index 4d177ce1d536..124cd2f93020 100644
> > > --- a/arch/arm64/kvm/hyp/pgtable.c
> > > +++ b/arch/arm64/kvm/hyp/pgtable.c
> > > @@ -223,7 +223,7 @@ static inline int __kvm_pgtable_visit(struct
> > kvm_pgtable_walk_data *data,
> > >  		goto out;
> > >
> > >  	if (!table) {
> > > -		data->addr += kvm_granule_size(level);
> > > +		data->addr = ALIGN(data->addr, kvm_granule_size(level));
>
> What if previous data->addr is already aligned with 
> kvm_granule_size(level)?
> Hence a deadloop? Am I missing anything else?

Indeed, well spotted. I'll revert to your original suggestion
if everybody agrees...

Thanks,

        M.
--
Jazz is not dead. It just smells funny...