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:

quoted

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 <redacted>
---
 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

[...]

quoted

+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