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

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Date:   Thu, 4 Mar 2021 09:22:22 +0000
From:   Will Deacon <will@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Justin He <Justin.He@....com>, kvmarm@...ts.cs.columbia.edu,
        James Morse <James.Morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki Poulose <Suzuki.Poulose@....com>,
        Catalin Marinas <Catalin.Marinas@....com>,
        Gavin Shan <gshan@...hat.com>,
        Yanan Wang <wangyanan55@...wei.com>,
        Quentin Perret <qperret@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Fix unaligned addr case in mmu walking

On Thu, Mar 04, 2021 at 09:16:25AM +0000, Marc Zyngier wrote:
> On 2021-03-04 00:46, Justin He wrote:
> > > 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@....com>
> > > > 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@...r.kernel.org
> > > > Reported-by: Howard Zhang <Howard.Zhang@....com>
> > > > Signed-off-by: Jia He <justin.he@....com>
> > > > Fixes: b1e57de62cfb ("KVM: arm64: Add stand-alone page-table walker
> > > infrastructure")
> > > > [maz: rewrite commit message]
> > > > Signed-off-by: Marc Zyngier <maz@...nel.org>
> > > > Link: https://lore.kernel.org/r/20210303024225.2591-1-justin.he@arm.com
> > > > ---
> > > >  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...

Heh, yeah, at least one of us is awake.
For the original patch, with the updated (including typo fix) commit
message:

Acked-by: Will Deacon <will@...nel.org>

If that still counts for anything!

Will