linux-kernel - Re: [PATCH v3 13/21] KVM: arm64: Expose host stage-2 manipulation helpers

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Date:   Tue, 3 Aug 2021 11:20:00 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Fuad Tabba <tabba@...gle.com>
Cc:     maz@...nel.org, james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, ardb@...nel.org, qwandor@...gle.com,
        dbrazdil@...gle.com, kernel-team@...roid.com
Subject: Re: [PATCH v3 13/21] KVM: arm64: Expose host stage-2 manipulation
 helpers

On Monday 02 Aug 2021 at 13:13:20 (+0200), Fuad Tabba wrote:
> Hi Quentin,
> 
> On Thu, Jul 29, 2021 at 3:28 PM Quentin Perret <qperret@...gle.com> wrote:
> >
> > We will need to manipulate the host stage-2 page-table from outside
> > mem_protect.c soon. Introduce two functions allowing this, and make
> > them usable to users of mem_protect.h.
> >
> > Signed-off-by: Quentin Perret <qperret@...gle.com>
> > ---
> >  arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |  2 ++
> >  arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 17 ++++++++++++++++-
> >  2 files changed, 18 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > index ae355bfd8c01..47c2a0c51612 100644
> > --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > @@ -49,6 +49,8 @@ extern struct host_kvm host_kvm;
> >  int __pkvm_prot_finalize(void);
> >  int __pkvm_mark_hyp(phys_addr_t start, phys_addr_t end);
> >
> > +int host_stage2_idmap_locked(u64 start, u64 end, enum kvm_pgtable_prot prot);
> > +int host_stage2_set_owner_locked(u64 start, u64 end, u8 owner_id);
> >  int kvm_host_prepare_stage2(void *pgt_pool_base);
> >  void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt);
> >
> > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > index 70c57d2c3024..a7f6134789e0 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > @@ -272,6 +272,21 @@ static int host_stage2_adjust_range(u64 addr, struct kvm_mem_range *range)
> >         return 0;
> >  }
> >
> > +int host_stage2_idmap_locked(u64 start, u64 end, enum kvm_pgtable_prot prot)
> > +{
> > +       hyp_assert_lock_held(&host_kvm.lock);
> > +
> > +       return host_stage2_try(__host_stage2_idmap, start, end, prot);
> > +}
> > +
> > +int host_stage2_set_owner_locked(u64 start, u64 end, u8 owner_id)
> > +{
> > +       hyp_assert_lock_held(&host_kvm.lock);
> > +
> > +       return host_stage2_try(kvm_pgtable_stage2_set_owner, &host_kvm.pgt,
> > +                              start, end - start, &host_s2_pool, owner_id);
> > +}
> 
> This is a potential issue elsewhere as well, but all functions in
> kvm_pgtable.h, including kvm_pgtable_stage2_set_owner, specify an
> address range via address and size. The two you have introduced here
> take a start and an end. I'm not sure if making these two consistent
> with the ones in kvm_pgtable.h would be good, or would just complicate
> things in other places.

Good point, and it looks like specifying these two with start-size
parameters would simplify the callers a tiny bit as well, so I'll fold
that in v4.

Thanks,
Quentin