KVM: PPC: Book3S HV: Flush guest mappings when turning dirty tracking on/off

This adds code to flush the partition-scoped page tables for a radix
guest when dirty tracking is turned on or off for a memslot.  Only the
guest real addresses covered by the memslot are flushed.  The reason
for this is to get rid of any 2M PTEs in the partition-scoped page
tables that correspond to host transparent huge pages, so that page
dirtiness is tracked at a system page (4k or 64k) granularity rather
than a 2M granularity.  The page tables are also flushed when turning
dirty tracking off so that the memslot's address space can be
repopulated with THPs if possible.

To do this, we add a new function kvmppc_radix_flush_memslot().  Since
this does what's needed for kvmppc_core_flush_memslot_hv() on a radix
guest, we now make kvmppc_core_flush_memslot_hv() call the new
kvmppc_radix_flush_memslot() rather than calling kvm_unmap_radix()
for each page in the memslot.  This has the effect of fixing a bug in
that kvmppc_core_flush_memslot_hv() was previously calling
kvm_unmap_radix() without holding the kvm->mmu_lock spinlock, which
is required to be held.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Reviewed-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/include/asm/kvm_book3s.h

@@ -222,6 +222,8 @@ extern int kvm_test_age_radix(struct kvm *kvm, struct kvm_memory_slot *memslot,
 			unsigned long gfn);
 extern long kvmppc_hv_get_dirty_log_radix(struct kvm *kvm,
 			struct kvm_memory_slot *memslot, unsigned long *map);
+extern void kvmppc_radix_flush_memslot(struct kvm *kvm,
+			const struct kvm_memory_slot *memslot);
 extern int kvmhv_get_rmmu_info(struct kvm *kvm, struct kvm_ppc_rmmu_info *info);
 
 /* XXX remove this export when load_last_inst() is generic */

arch/powerpc/kvm/book3s_64_mmu_hv.c

@@ -899,11 +899,12 @@ void kvmppc_core_flush_memslot_hv(struct kvm *kvm,
 
 	gfn = memslot->base_gfn;
 	rmapp = memslot->arch.rmap;
+	if (kvm_is_radix(kvm)) {
+		kvmppc_radix_flush_memslot(kvm, memslot);
+		return;
+	}
+
 	for (n = memslot->npages; n; --n, ++gfn) {
-		if (kvm_is_radix(kvm)) {
-			kvm_unmap_radix(kvm, memslot, gfn);
-			continue;
-		}
 		/*
 		 * Testing the present bit without locking is OK because
 		 * the memslot has been marked invalid already, and hence

arch/powerpc/kvm/book3s_64_mmu_radix.c

@@ -958,6 +958,26 @@ long kvmppc_hv_get_dirty_log_radix(struct kvm *kvm,
 	return 0;
 }
 
+void kvmppc_radix_flush_memslot(struct kvm *kvm,
+				const struct kvm_memory_slot *memslot)
+{
+	unsigned long n;
+	pte_t *ptep;
+	unsigned long gpa;
+	unsigned int shift;
+
+	gpa = memslot->base_gfn << PAGE_SHIFT;
+	spin_lock(&kvm->mmu_lock);
+	for (n = memslot->npages; n; --n) {
+		ptep = __find_linux_pte(kvm->arch.pgtable, gpa, NULL, &shift);
+		if (ptep && pte_present(*ptep))
+			kvmppc_unmap_pte(kvm, ptep, gpa, shift, memslot,
+					 kvm->arch.lpid);
+		gpa += PAGE_SIZE;
+	}
+	spin_unlock(&kvm->mmu_lock);
+}
+
 static void add_rmmu_ap_encoding(struct kvm_ppc_rmmu_info *info,
 				 int psize, int *indexp)
 {

arch/powerpc/kvm/book3s_hv.c

@@ -4384,6 +4384,23 @@ static void kvmppc_core_commit_memory_region_hv(struct kvm *kvm,
 	 */
 	if (npages)
 		atomic64_inc(&kvm->arch.mmio_update);
+
+	/*
+	 * For change == KVM_MR_MOVE or KVM_MR_DELETE, higher levels
+	 * have already called kvm_arch_flush_shadow_memslot() to
+	 * flush shadow mappings.  For KVM_MR_CREATE we have no
+	 * previous mappings.  So the only case to handle is
+	 * KVM_MR_FLAGS_ONLY when the KVM_MEM_LOG_DIRTY_PAGES bit
+	 * has been changed.
+	 * For radix guests, we flush on setting KVM_MEM_LOG_DIRTY_PAGES
+	 * to get rid of any THP PTEs in the partition-scoped page tables
+	 * so we can track dirtiness at the page level; we flush when
+	 * clearing KVM_MEM_LOG_DIRTY_PAGES so that we can go back to
+	 * using THP PTEs.
+	 */
+	if (change == KVM_MR_FLAGS_ONLY && kvm_is_radix(kvm) &&
+	    ((new->flags ^ old->flags) & KVM_MEM_LOG_DIRTY_PAGES))
+		kvmppc_radix_flush_memslot(kvm, old);
 }
 
 /*