[PATCH v5 02/19] KVM: Reinstall old memslots if arch preparation fails

Sean Christopherson
2020-01-21T22:32:07Z

Reinstall the old memslots if preparing the new memory region fails
after invalidating a to-be-{re}moved memslot.

Remove the superfluous 'old_memslots' variable so that it's somewhat
clear that the error handling path needs to free the unused memslots,
not simply the 'old' memslots.

Fixes: bc6678a33d9b9 ("KVM: introduce kvm->srcu and convert kvm_set_memory_region to SRCU update")
Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
virt/kvm/kvm_main.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index eb3709d55139..1429d8b726ea 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -998,7 +998,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
unsigned long npages;
struct kvm_memory_slot *slot;
struct kvm_memory_slot old, new;
- struct kvm_memslots *slots = NULL, *old_memslots;
+ struct kvm_memslots *slots;
int as_id, id;
enum kvm_mr_change change;

@@ -1106,7 +1106,13 @@ int __kvm_set_memory_region(struct kvm *kvm,
slot = id_to_memslot(slots, id);
slot->flags |= KVM_MEMSLOT_INVALID;

- old_memslots = install_new_memslots(kvm, as_id, slots);
+ /*
+ * We can re-use the old memslots, the only difference from the
+ * newly installed memslots is the invalid flag, which will get
+ * dropped by update_memslots anyway. We'll also revert to the
+ * old memslots if preparing the new memory region fails.
+ */
+ slots = install_new_memslots(kvm, as_id, slots);

/* From this point no new shadow pages pointing to a deleted,
* or moved, memslot will be created.
@@ -1116,13 +1122,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
* - kvm_is_visible_gfn (mmu_check_root)
*/
kvm_arch_flush_shadow_memslot(kvm, slot);
-
- /*
- * We can re-use the old_memslots from above, the only difference
- * from the currently installed memslots is the invalid flag. This
- * will get overwritten by update_memslots anyway.
- */
- slots = old_memslots;
}

r = kvm_arch_prepare_memory_region(kvm, &new, mem, change);
@@ -1136,15 +1135,17 @@ int __kvm_set_memory_region(struct kvm *kvm,
}

update_memslots(slots, &new, change);
- old_memslots = install_new_memslots(kvm, as_id, slots);
+ slots = install_new_memslots(kvm, as_id, slots);

kvm_arch_commit_memory_region(kvm, mem, &old, &new, change);

kvm_free_memslot(kvm, &old, &new);
- kvfree(old_memslots);
+ kvfree(slots);
return 0;

out_slots:
+ if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
+ slots = install_new_memslots(kvm, as_id, slots);
kvfree(slots);
out_free:
kvm_free_memslot(kvm, &new, &old);
--
2.24.1