Re: [PATCH v5 2/6] KVM: arm64: Move D-cache flush to the fault handlers

On Wednesday 02 Jun 2021 at 11:19:49 (+0100), Marc Zyngier wrote:

On Thu, 15 Apr 2021 12:50:28 +0100,

quoted

@@ -583,6 +589,7 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 {
 	kvm_pte_t new, old = *ptep;
 	u64 granule = kvm_granule_size(level), phys = data->phys;
+	struct kvm_pgtable *pgt = data->mmu->pgt;
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
 
 	if (!kvm_block_mapping_supported(addr, end, phys, level))

@@ -606,6 +613,13 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 		stage2_put_pte(ptep, data->mmu, addr, level, mm_ops);
 	}
 
+	/* Perform CMOs before installation of the guest stage-2 PTE */
+	if (pgt->flags & KVM_PGTABLE_S2_GUEST) {
+		if (stage2_pte_cacheable(pgt, new) && !stage2_has_fwb(pgt))
+			__flush_dcache_area(mm_ops->phys_to_virt(phys),
+					    granule);
+	}

Rather than this, why not provide new callbacks in mm_ops, even if we
have to provide one that is specific to guests (and let the protected
stuff do its own thing)?

Ack, an optional callback in the mm_ops sounds much nicer.

One thing I really dislike though is that the page-table code is
starting to be littered with things that are not directly related to
page tables. We are re-creating the user_mem_abort() mess in a
different place.

+1, we should probably keep the page-table code as close as possible
to a standalone and architecturally-compliant library as opposed to a
mess of unrelated logic, simply because that will lead to a cleaner and
more maintainable design in the long run, and because that will ease the
interoperability with EL2 in protected mode.

Thanks,
Quentin