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The shift fits if the distance is no greater than the number of leading zeroes in mask. Use that directly. Convert delta to u64 before negating it so that a positive delta, including one that wrapped to S64_MIN, is rejected by the unsigned comparison without invoking signed overflow. Use __builtin_clzl() to match the unsigned long type of mask on both 32-bit and 64-bit builds. Suggested-by: Paolo Bonzini Signed-off-by: Peng Hao --- virt/kvm/dirty_ring.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c index 572b854edf74..8f39047ae7ab 100644 --- a/virt/kvm/dirty_ring.c +++ b/virt/kvm/dirty_ring.c @@ -170,9 +170,8 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring, continue; } - /* Backwards visit, careful about overflows! */ - if (delta > -BITS_PER_LONG && delta < 0 && - (mask << -delta >> -delta) == mask) { + /* Backwards visit, but do not discard set bits. */ + if (-(u64)delta <= __builtin_clzl(mask)) { cur_offset = next_offset; mask = (mask << -delta) | 1; continue; -- 2.43.7