On 5/8/2025 10:10 PM, Sean Christopherson wrote:
Cap the number of ring entries that are reset in a single ioctl to INT_MAX
to ensure userspace isn't confused by a wrap into negative space, and so
that, in a truly pathological scenario, KVM doesn't miss a TLB flush due
to the count wrapping to zero. While the size of the ring is fixed at
0x10000 entries and KVM (currently) supports at most 4096, userspace is
allowed to harvest entries from the ring while the reset is in-progress,
i.e. it's possible for the ring to always have harvested entries.
Opportunistically return an actual error code from the helper so that a
future fix to handle pending signals can gracefully return -EINTR.
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Yan Zhao <yan.y.zhao@xxxxxxxxx>
Cc: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
Fixes: fb04a1eddb1a ("KVM: X86: Implement ring-based dirty memory tracking")
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
include/linux/kvm_dirty_ring.h | 8 +++++---
virt/kvm/dirty_ring.c | 10 +++++-----
virt/kvm/kvm_main.c | 9 ++++++---
3 files changed, 16 insertions(+), 11 deletions(-)
diff --git a/include/linux/kvm_dirty_ring.h b/include/linux/kvm_dirty_ring.h
index da4d9b5f58f1..ee61ff6c3fe4 100644
--- a/include/linux/kvm_dirty_ring.h
+++ b/include/linux/kvm_dirty_ring.h
@@ -49,9 +49,10 @@ static inline int kvm_dirty_ring_alloc(struct kvm *kvm, struct kvm_dirty_ring *r
}
static inline int kvm_dirty_ring_reset(struct kvm *kvm,
- struct kvm_dirty_ring *ring)
+ struct kvm_dirty_ring *ring,
+ int *nr_entries_reset)
{
- return 0;
+ return -ENOENT;
}
static inline void kvm_dirty_ring_push(struct kvm_vcpu *vcpu,
@@ -82,7 +83,8 @@ int kvm_dirty_ring_alloc(struct kvm *kvm, struct kvm_dirty_ring *ring,
* called with kvm->slots_lock held, returns the number of
* processed pages.
*/
The comment should be updated as well, since the return value is not the
number of processed pages now.
-int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring);
+int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring,
+ int *nr_entries_reset);
[...]
