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KVM: Move memslot deletion to helper function

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Move memslot deletion into its own routine so that the success path for
other memslot updates does not need to use kvm_free_memslot(), i.e. can
explicitly destroy the dirty bitmap when necessary.  This paves the way
for dropping @dont from kvm_free_memslot(), i.e. all callers now pass
NULL for @dont.

Add a comment above the code to make a copy of the existing memslot
prior to deletion, it is not at all obvious that the pointer will become
stale during sorting and/or installation of new memslots.

Note, kvm_arch_commit_memory_region() allows an architecture to free
resources when moving a memslot or changing its flags, e.g. x86 frees
its arch specific memslot metadata during commit_memory_region().

Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Tested-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2020-02-18 13:07:26 -08:00 committed by Paolo Bonzini
parent 21198846de
commit 5c0b4f3d5c
1 changed files with 46 additions and 29 deletions
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75
virt/kvm/kvm_main.c
View File

@ -1043,6 +1043,27 @@ out_slots:
return r;
}
static int kvm_delete_memslot(struct kvm *kvm,
const struct kvm_userspace_memory_region *mem,
struct kvm_memory_slot *old, int as_id)
{
struct kvm_memory_slot new;
int r;
if (!old->npages)
return -EINVAL;
memset(&new, 0, sizeof(new));
new.id = old->id;
r = kvm_set_memslot(kvm, mem, old, &new, as_id, KVM_MR_DELETE);
if (r)
return r;
kvm_free_memslot(kvm, old, NULL);
return 0;
}
/*
* Allocate some memory and give it an address in the guest physical address
* space.
@ -1092,7 +1113,17 @@ int __kvm_set_memory_region(struct kvm *kvm,
if (npages > KVM_MEM_MAX_NR_PAGES)
return -EINVAL;
new = old = *slot;
/*
* Make a full copy of the old memslot, the pointer will become stale
* when the memslots are re-sorted by update_memslots(), and the old
* memslot needs to be referenced after calling update_memslots(), e.g.
* to free its resources and for arch specific behavior.
*/
old = *slot;
if (!mem->memory_size)
return kvm_delete_memslot(kvm, mem, &old, as_id);
new = old;
new.id = id;
new.base_gfn = base_gfn;
@ -1100,29 +1131,20 @@ int __kvm_set_memory_region(struct kvm *kvm,
new.flags = mem->flags;
new.userspace_addr = mem->userspace_addr;
if (npages) {
if (!old.npages)
change = KVM_MR_CREATE;
else { /* Modify an existing slot. */
if ((new.userspace_addr != old.userspace_addr) ||
(npages != old.npages) ||
((new.flags ^ old.flags) & KVM_MEM_READONLY))
return -EINVAL;
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. */
return 0;
}
} else {
if (!old.npages)
if (!old.npages) {
change = KVM_MR_CREATE;
} else { /* Modify an existing slot. */
if ((new.userspace_addr != old.userspace_addr) ||
(npages != old.npages) ||
((new.flags ^ old.flags) & KVM_MEM_READONLY))
return -EINVAL;
change = KVM_MR_DELETE;
new.base_gfn = 0;
new.flags = 0;
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. */
return 0;
}
if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
@ -1145,17 +1167,12 @@ int __kvm_set_memory_region(struct kvm *kvm,
return r;
}
/* actual memory is freed via old in kvm_free_memslot below */
if (change == KVM_MR_DELETE) {
new.dirty_bitmap = NULL;
memset(&new.arch, 0, sizeof(new.arch));
}
r = kvm_set_memslot(kvm, mem, &old, &new, as_id, change);
if (r)
goto out_bitmap;
kvm_free_memslot(kvm, &old, &new);
if (old.dirty_bitmap && !new.dirty_bitmap)
kvm_destroy_dirty_bitmap(&old);
return 0;
out_bitmap: