linux-kernel - Re: [PATCH 02/14] KVM: arm64: Tear down unlinked stage-2 subtree after break-before-make

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Date:   Mon, 10 Oct 2022 03:58:25 +0000
From:   Oliver Upton <oliver.upton@...ux.dev>
To:     Ricardo Koller <ricarkol@...gle.com>
Cc:     Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        Reiji Watanabe <reijiw@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Ben Gardon <bgardon@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Gavin Shan <gshan@...hat.com>, Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/14] KVM: arm64: Tear down unlinked stage-2 subtree
 after break-before-make

Hey Ricardo,

On Tue, Sep 13, 2022 at 05:20:11PM -0700, Ricardo Koller wrote:

[...]

> > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> > index d8127c25424c..5c0c8028d71c 100644
> > --- a/arch/arm64/kvm/hyp/pgtable.c
> > +++ b/arch/arm64/kvm/hyp/pgtable.c
> > @@ -763,17 +763,21 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
> >  	return 0;
> >  }
> >  
> > +static int stage2_map_walk_leaf(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
> > +				struct stage2_map_data *data);
> > +
> >  static int stage2_map_walk_table_pre(u64 addr, u64 end, u32 level,
> >  				     kvm_pte_t *ptep,
> >  				     struct stage2_map_data *data)
> >  {
> > -	if (data->anchor)
> > -		return 0;
> > +	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
> > +	kvm_pte_t *childp = kvm_pte_follow(*ptep, mm_ops);
> > +	struct kvm_pgtable *pgt = data->mmu->pgt;
> > +	int ret;
> >  
> >  	if (!stage2_leaf_mapping_allowed(addr, end, level, data))
> >  		return 0;
> >  
> > -	data->childp = kvm_pte_follow(*ptep, data->mm_ops);
> >  	kvm_clear_pte(ptep);
> >  
> >  	/*
> > @@ -782,8 +786,13 @@ static int stage2_map_walk_table_pre(u64 addr, u64 end, u32 level,
> >  	 * individually.
> >  	 */
> >  	kvm_call_hyp(__kvm_tlb_flush_vmid, data->mmu);
> > -	data->anchor = ptep;
> > -	return 0;
> > +
> > +	ret = stage2_map_walk_leaf(addr, end, level, ptep, data);
> 
> I think this always ends up calling stage2_map_walker_try_leaf() (at
> least it should). In that case, I think it might be clearer to do so, as
> the intention is to just install a block.

Yikes, I missed this in v2. I do agree with your point, it reads a bit
odd to call something that could reinstall a table.

Picked up the fix for v3. Thanks!

--
Best,
Oliver