KVM: arm64: Move guest CMOs to the fault handlers

We currently uniformly perform CMOs of D-cache and I-cache in function
user_mem_abort before calling the fault handlers. If we get concurrent
guest faults(e.g. translation faults, permission faults) or some really
unnecessary guest faults caused by BBM, CMOs for the first vcpu are
necessary while the others later are not.

By moving CMOs to the fault handlers, we can easily identify conditions
where they are really needed and avoid the unnecessary ones. As it's a
time consuming process to perform CMOs especially when flushing a block
range, so this solution reduces much load of kvm and improve efficiency
of the stage-2 page table code.

We can imagine two specific scenarios which will gain much benefit:
1) In a normal VM startup, this solution will improve the efficiency of
handling guest page faults incurred by vCPUs, when initially populating
stage-2 page tables.
2) After live migration, the heavy workload will be resumed on the
destination VM, however all the stage-2 page tables need to be rebuilt
at the moment. So this solution will ease the performance drop during
resuming stage.

Reviewed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210617105824.31752-5-wangyanan55@huawei.com

1 files changed, 7 insertions, 14 deletions

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 0a5a5b098a4a..0b3ba57849f6 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -442,6 +442,8 @@ static struct kvm_pgtable_mm_ops kvm_s2_mm_ops = {
 	.page_count		= kvm_host_page_count,
 	.phys_to_virt		= kvm_host_va,
 	.virt_to_phys		= kvm_host_pa,
+	.dcache_clean_inval_poc	= clean_dcache_guest_page,
+	.icache_inval_pou	= invalidate_icache_guest_page,
 };
 
 /**
@@ -971,15 +973,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	if (writable)
 		prot |= KVM_PGTABLE_PROT_W;
 
-	if (fault_status != FSC_PERM && !device)
-		clean_dcache_guest_page(page_address(pfn_to_page(pfn)),
-					vma_pagesize);
-
-	if (exec_fault) {
+	if (exec_fault)
 		prot |= KVM_PGTABLE_PROT_X;
-		invalidate_icache_guest_page(page_address(pfn_to_page(pfn)),
-					     vma_pagesize);
-	}
 
 	if (device)
 		prot |= KVM_PGTABLE_PROT_DEVICE;
@@ -1177,12 +1172,10 @@ bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 	WARN_ON(range->end - range->start != 1);
 
 	/*
-	 * We've moved a page around, probably through CoW, so let's treat it
-	 * just like a translation fault and clean the cache to the PoC.
-	 */
-	clean_dcache_guest_page(page_address(pfn_to_page(pfn)), PAGE_SIZE);
-
-	/*
+	 * We've moved a page around, probably through CoW, so let's treat
+	 * it just like a translation fault and the map handler will clean
+	 * the cache to the PoC.
+	 *
 	 * The MMU notifiers will have unmapped a huge PMD before calling
 	 * ->change_pte() (which in turn calls kvm_set_spte_gfn()) and
 	 * therefore we never need to clear out a huge PMD through this