On Fri, Aug 19, 2022 at 12:37:42PM -0700, Vishal Annapurve wrote:

quoted

...

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 230c8ff9659c..bb714c2a4b06 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c

@@ -914,6 +914,35 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)

 #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */

+#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
+#define KVM_MEM_ATTR_PRIVATE   0x0001
+static int kvm_vm_ioctl_set_encrypted_region(struct kvm *kvm, unsigned int ioctl,
+                                            struct kvm_enc_region *region)
+{
+       unsigned long start, end;
+       void *entry;
+       int r;
+
+       if (region->size == 0 || region->addr + region->size < region->addr)
+               return -EINVAL;
+       if (region->addr & (PAGE_SIZE - 1) || region->size & (PAGE_SIZE - 1))
+               return -EINVAL;
+
+       start = region->addr >> PAGE_SHIFT;
+       end = (region->addr + region->size - 1) >> PAGE_SHIFT;
+
+       entry = ioctl == KVM_MEMORY_ENCRYPT_REG_REGION ?
+                               xa_mk_value(KVM_MEM_ATTR_PRIVATE) : NULL;
+
+       r = xa_err(xa_store_range(&kvm->mem_attr_array, start, end,
+                                       entry, GFP_KERNEL_ACCOUNT));

xa_store_range seems to create multi-index entries by default.
Subsequent xa_store_range call changes all the entries stored
previously.

By using xa_store_range and storing them as multi-index entries I
expected to save some memory for continuous pages originally.

But sounds like the current multi-index store behaviour isn't quite
ready for our usage.

Chao

xa_store needs to be used here instead of xa_store_range to achieve
the intended behavior.

quoted

+
+       kvm_zap_gfn_range(kvm, start, end + 1);
+
+       return r;
+}
+#endif /* CONFIG_HAVE_KVM_PRIVATE_MEM */
+
...