linux-kernel - Re: [PATCH v3 24/32] KVM: arm64: Reserve memory for host stage 2

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Date:   Fri, 5 Mar 2021 09:17:16 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     Will Deacon <will@...nel.org>
Cc:     catalin.marinas@....com, maz@...nel.org, james.morse@....com,
        julien.thierry.kdev@...il.com, suzuki.poulose@....com,
        android-kvm@...gle.com, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com, kvmarm@...ts.cs.columbia.edu,
        linux-arm-kernel@...ts.infradead.org, tabba@...gle.com,
        mark.rutland@....com, dbrazdil@...gle.com, mate.toth-pal@....com,
        seanjc@...gle.com, robh+dt@...nel.org
Subject: Re: [PATCH v3 24/32] KVM: arm64: Reserve memory for host stage 2

On Thursday 04 Mar 2021 at 19:49:53 (+0000), Will Deacon wrote:
> On Tue, Mar 02, 2021 at 02:59:54PM +0000, Quentin Perret wrote:
> > Extend the memory pool allocated for the hypervisor to include enough
> > pages to map all of memory at page granularity for the host stage 2.
> > While at it, also reserve some memory for device mappings.
> > 
> > Signed-off-by: Quentin Perret <qperret@...gle.com>
> > ---
> >  arch/arm64/kvm/hyp/include/nvhe/mm.h | 23 ++++++++++++++++++++++-
> >  arch/arm64/kvm/hyp/nvhe/setup.c      | 12 ++++++++++++
> >  arch/arm64/kvm/hyp/reserved_mem.c    |  2 ++
> >  3 files changed, 36 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h
> > index ac0f7fcffd08..411a35db949c 100644
> > --- a/arch/arm64/kvm/hyp/include/nvhe/mm.h
> > +++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h
> > @@ -53,7 +53,7 @@ static inline unsigned long __hyp_pgtable_max_pages(unsigned long nr_pages)
> >  	return total;
> >  }
> >  
> > -static inline unsigned long hyp_s1_pgtable_pages(void)
> > +static inline unsigned long __hyp_pgtable_total_pages(void)
> >  {
> >  	unsigned long res = 0, i;
> >  
> > @@ -63,9 +63,30 @@ static inline unsigned long hyp_s1_pgtable_pages(void)
> >  		res += __hyp_pgtable_max_pages(reg->size >> PAGE_SHIFT);
> >  	}
> >  
> > +	return res;
> > +}
> > +
> > +static inline unsigned long hyp_s1_pgtable_pages(void)
> > +{
> > +	unsigned long res;
> > +
> > +	res = __hyp_pgtable_total_pages();
> > +
> >  	/* Allow 1 GiB for private mappings */
> >  	res += __hyp_pgtable_max_pages(SZ_1G >> PAGE_SHIFT);
> >  
> >  	return res;
> >  }
> > +
> > +static inline unsigned long host_s2_mem_pgtable_pages(void)
> > +{
> > +	return __hyp_pgtable_total_pages() + 16;
> 
> Is this 16 due to the possibility of a concatenated pgd?

Yes it is, to be sure we have a safe upper-bound.

> If so, please add a comment to that effect.

Will do, thanks.
Quentin