Re: [PATCH RESEND v2 15/17] KVM: selftests: Add dirty ring buffer test

Peter Xu
2019-12-24T15:22:53Z

On Tue, Dec 24, 2019 at 02:18:37PM +0800, Jason Wang wrote:

[...]

> > + while (fetch != avail) {
> > + cur = &dirty_gfns[fetch % TEST_DIRTY_RING_COUNT];
> > + TEST_ASSERT(cur->pad == 0, "Padding is non-zero: 0x%x", cur->pad);
> > + TEST_ASSERT(cur->slot == slot, "Slot number didn't match: "
> > + "%u != %u", cur->slot, slot);
> > + TEST_ASSERT(cur->offset < num_pages, "Offset overflow: "
> > + "0x%llx >= 0x%llx", cur->offset, num_pages);
> > + DEBUG("fetch 0x%x offset 0x%llx\n", fetch, cur->offset);
> > + test_and_set_bit(cur->offset, bitmap);
> > + fetch++;
>
>
> Any reason to use test_and_set_bit()? I guess set_bit() should be
> sufficient.

Yes.

>
>
> > + count++;
> > + }
> > + WRITE_ONCE(indices->fetch_index, fetch);
>
>
> Is WRITE_ONCE a must here?

No.

[...]

> > +void *vcpu_map_dirty_ring(struct kvm_vm *vm, uint32_t vcpuid)
> > +{
> > + struct vcpu *vcpu;
> > + uint32_t size = vm->dirty_ring_size;
> > +
> > + TEST_ASSERT(size > 0, "Should enable dirty ring first");
> > +
> > + vcpu = vcpu_find(vm, vcpuid);
> > +
> > + TEST_ASSERT(vcpu, "Cannot find vcpu %u", vcpuid);
> > +
> > + if (!vcpu->dirty_gfns) {
> > + vcpu->dirty_gfns_count = size / sizeof(struct kvm_dirty_gfn);
> > + vcpu->dirty_gfns = mmap(NULL, size, PROT_READ | PROT_WRITE,
> > + MAP_SHARED, vcpu->fd, vm->page_size *
> > + KVM_DIRTY_LOG_PAGE_OFFSET);
>
>
> It looks to me that we don't write to dirty_gfn.
>
> So PROT_READ should be sufficient.

Yes. Thanks,

--
Peter Xu