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SubjectRe: [RFC PATCH v2 26/26] KVM: arm64: Wrap the host with a stage 2
On Thu, Feb 04, 2021 at 02:26:35PM +0000, Quentin Perret wrote:
> 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 <qperret@google.com>
> > > ---
> > > 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 ... :)

Awesome! The Stage-2 TLB thanks you.

Will

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