Fix issues with dirty ring harvesting where KVM doesn't bound the processing
of entries in any way, which allows userspace to keep KVM in a tight loop
indefinitely.
E.g.
struct kvm_dirty_gfn *dirty_gfns = vcpu_map_dirty_ring(vcpu);
if (fork()) {
int r;
for (;;) {
r = kvm_vm_reset_dirty_ring(vcpu->vm);
if (r)
printf("RESET %d dirty ring entries\n", r);
}
} else {
int i;
for (i = 0; i < test_dirty_ring_count; i++) {
dirty_gfns[i].slot = TEST_MEM_SLOT_INDEX;
dirty_gfns[i].offset = (i * 64) % host_num_pages;
}
for (;;) {
for (i = 0; i < test_dirty_ring_count; i++)
WRITE_ONCE(dirty_gfns[i].flags, KVM_DIRTY_GFN_F_RESET);
}
}
Patches 1-3 address that class of bugs. Patches 4-6 are cleanups.
v3:
- Fix typos (I apparently can't spell opportunistically to save my life).
[Binbin, James]
- Clean up stale comments. [Binbin]
- Collect reviews. [James, Pankaj]
- Add a lockdep assertion on slots_lock, along with a comment. [James]
v2:
- https://lore.kernel.org/all/20250508141012.1411952-1-seanjc@xxxxxxxxxx
- Expand on comments in dirty ring harvesting code. [Yan]
v1: https://lore.kernel.org/all/20250111010409.1252942-1-seanjc@xxxxxxxxxx
Sean Christopherson (6):
KVM: Bound the number of dirty ring entries in a single reset at
INT_MAX
KVM: Bail from the dirty ring reset flow if a signal is pending
KVM: Conditionally reschedule when resetting the dirty ring
KVM: Check for empty mask of harvested dirty ring entries in caller
KVM: Use mask of harvested dirty ring entries to coalesce dirty ring
resets
KVM: Assert that slots_lock is held when resetting per-vCPU dirty
rings
include/linux/kvm_dirty_ring.h | 18 ++----
virt/kvm/dirty_ring.c | 111 +++++++++++++++++++++++----------
virt/kvm/kvm_main.c | 9 ++-
3 files changed, 89 insertions(+), 49 deletions(-)
base-commit: 7ef51a41466bc846ad794d505e2e34ff97157f7f
--
2.49.0.1112.g889b7c5bd8-goog
