Re: [RFC PATCH v2 00/26] KVM/arm64: A stage 2 for the host

We tested the pKVM changes pulled from here:

quoted

     https://android-kvm.googlesource.com/linux qperret/host-stage2-v2

We were using a target with Arm architecture with FEAT_S2FWB, and found that
there is a bug in the patch.


It turned out that the Kernel checks for the extension, and sets up the
stage 2 translation so that it forces the host memory type to write-through.
However it seems that the code doesn't turn on the feature in the HCR_EL2
register.


We were able to fix the issue by applying the following patch:

diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c

b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 0cd3eb178f3b..e8521a072ea6 100644

--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c

@@ -105,6 +105,8 @@ int kvm_host_prepare_stage2(void *mem_pgt_pool, void

*dev_pgt_pool)
                params->vttbr = kvm_get_vttbr(mmu);
                params->vtcr = host_kvm.arch.vtcr;
                params->hcr_el2 |= HCR_VM;
+               if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB))
+                       params->hcr_el2 |= HCR_FWB;
                __flush_dcache_area(params, sizeof(*params));
        }