Subject: Re: [RFC PATCH v2 26/26] KVM: arm64: Wrap the host with a stage 2

From: Quentin Perret <[email-masked]>
Date: Thu, 4 Feb 2021 14:26:35 +0000

On Wednesday 03 Feb 2021 at 16:11:47 (+0000), Will Deacon wrote:
> On Fri, Jan 08, 2021 at 12:15:24PM +0000, Quentin Perret wrote:
> > When KVM runs in protected nVHE mode, make use of a stage 2 page-table
> > to give the hypervisor some control over the host memory accesses. At
> > the moment all memory aborts from the host will be instantly idmapped
> > RWX at stage 2 in a lazy fashion. Later patches will make use of that
> > infrastructure to implement access control restrictions to e.g. protect
> > guest memory from the host.
> > 
> > Signed-off-by: Quentin Perret <[email-masked]>
> > ---
> >  arch/arm64/include/asm/kvm_cpufeature.h       |   2 +
> >  arch/arm64/kernel/image-vars.h                |   3 +
> >  arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |  33 +++
> >  arch/arm64/kvm/hyp/nvhe/Makefile              |   2 +-
> >  arch/arm64/kvm/hyp/nvhe/hyp-init.S            |   1 +
> >  arch/arm64/kvm/hyp/nvhe/hyp-main.c            |   6 +
> >  arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 191 ++++++++++++++++++
> >  arch/arm64/kvm/hyp/nvhe/setup.c               |   6 +
> >  arch/arm64/kvm/hyp/nvhe/switch.c              |   7 +-
> >  arch/arm64/kvm/hyp/nvhe/tlb.c                 |   4 +-
> >  10 files changed, 248 insertions(+), 7 deletions(-)
> >  create mode 100644 arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> >  create mode 100644 arch/arm64/kvm/hyp/nvhe/mem_protect.c
> 
> [...]
> 
> > +void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt)
> > +{
> > +	enum kvm_pgtable_prot prot;
> > +	u64 far, hpfar, esr, ipa;
> > +	int ret;
> > +
> > +	esr = read_sysreg_el2(SYS_ESR);
> > +	if (!__get_fault_info(esr, &far, &hpfar))
> > +		hyp_panic();
> > +
> > +	prot = KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W | KVM_PGTABLE_PROT_X;
> > +	ipa = (hpfar & HPFAR_MASK) << 8;
> > +	ret = host_stage2_map(ipa, PAGE_SIZE, prot);
> 
> Can we try to put down a block mapping if the whole thing falls within
> memory?

Yes we can! And in fact we can do that outside of memory too. It's
queued for v3 already, so stay tuned ... :)

Thanks,
Quentin

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