KVM_SET_USER_MEMORY_REGION forces __kvm_set_memory_region() to identify
what kind of change is being requested by checking the parameters. The
current code does this checking at various points in code and each
condition used there is not easy to understand at first glance.
This patch consolidates these and introduces an enum to name the
possible changes to clean up the code.
Although this does not introduce any user visible changes, there are two
changes which optimize the code a bit:
1. If we have nothing to change, the new code returns immediately.
2. If we just modify the flags, no changes about the mapping, the
new code does not call kvm_iommu_map_pages().
One interesting thing we noticed was about the case 1. Although this
case seemed unimportant, QEMU was relying on the current behaviour:
when we returned a value other than 0, e.g. -EINVAL, live migration
failed at the final stage with a section mismatch error.
Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@xxxxxxxxxxxxx>
---
virt/kvm/kvm_main.c | 64 +++++++++++++++++++++++++++++++++++----------------
1 files changed, 44 insertions(+), 20 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8cb4e71..5426e96 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -714,6 +714,24 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
}
/*
+ * KVM_SET_USER_MEMORY_REGION ioctl allows the following operations:
+ * - create a new memory slot
+ * - delete an existing memory slot
+ * - modify an existing memory slot
+ * -- move it in the guest physical memory space
+ * -- just change its flags
+ *
+ * Since flags can be changed by some of these operations, the following
+ * differentiation is the best we can do for __kvm_set_memory_region():
+ */
+enum kvm_mr_change {
+ KVM_MR_CREATE,
+ KVM_MR_DELETE,
+ KVM_MR_MOVE,
+ KVM_MR_FLAGS_ONLY,
+};
+
+/*
* Allocate some memory and give it an address in the guest physical address
* space.
*
@@ -731,6 +749,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
struct kvm_memory_slot *slot;
struct kvm_memory_slot old, new;
struct kvm_memslots *slots = NULL, *old_memslots;
+ enum kvm_mr_change change;
r = check_memory_region_flags(mem);
if (r)
@@ -772,17 +791,30 @@ int __kvm_set_memory_region(struct kvm *kvm,
new.npages = npages;
new.flags = mem->flags;
- /*
- * Disallow changing a memory slot's size or changing anything about
- * zero sized slots that doesn't involve making them non-zero.
- */
r = -EINVAL;
- if (npages && old.npages && npages != old.npages)
- goto out;
- if (!npages && !old.npages)
+ if (npages) {
+ if (!old.npages)
+ change = KVM_MR_CREATE;
+ else { /* Modify an existing slot. */
+ if ((mem->userspace_addr != old.userspace_addr) ||
+ (npages != old.npages))
+ goto out;
+
+ if (base_gfn != old.base_gfn)
+ change = KVM_MR_MOVE;
+ else if (new.flags != old.flags)
+ change = KVM_MR_FLAGS_ONLY;
+ else { /* Nothing to change. */
+ r = 0;
+ goto out;
+ }
+ }
+ } else if (old.npages) {
+ change = KVM_MR_DELETE;
+ } else /* Modify a non-existent slot: disallowed. */
goto out;
- if ((npages && !old.npages) || (base_gfn != old.base_gfn)) {
+ if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
/* Check for overlaps */
r = -EEXIST;
kvm_for_each_memslot(slot, kvm->memslots) {
@@ -800,20 +832,12 @@ int __kvm_set_memory_region(struct kvm *kvm,
new.dirty_bitmap = NULL;
r = -ENOMEM;
-
- /*
- * Allocate if a slot is being created. If modifying a slot,
- * the userspace_addr cannot change.
- */
- if (!old.npages) {
+ if (change == KVM_MR_CREATE) {
new.user_alloc = user_alloc;
new.userspace_addr = mem->userspace_addr;
if (kvm_arch_create_memslot(&new, npages))
goto out_free;
- } else if (npages && mem->userspace_addr != old.userspace_addr) {
- r = -EINVAL;
- goto out_free;
}
/* Allocate page dirty bitmap if needed */
@@ -823,7 +847,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
/* destroy any largepage mappings for dirty tracking */
}
- if (!npages || base_gfn != old.base_gfn) {
+ if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) {
r = -ENOMEM;
slots = kmemdup(kvm->memslots, sizeof(struct kvm_memslots),
GFP_KERNEL);
@@ -865,14 +889,14 @@ int __kvm_set_memory_region(struct kvm *kvm,
}
/* map new memory slot into the iommu */
- if (npages) {
+ if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
r = kvm_iommu_map_pages(kvm, &new);
if (r)
goto out_slots;
}
/* actual memory is freed via old in kvm_free_physmem_slot below */
- if (!npages) {
+ if (change == KVM_MR_DELETE) {
new.dirty_bitmap = NULL;
memset(&new.arch, 0, sizeof(new.arch));
}
--
1.7.5.4
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