On Thu, 25 Aug 2022 23:26:04 +0100
Joao Martins <joao.m.martins@xxxxxxxxxx> wrote:
> On 8/25/22 21:49, Alex Williamson wrote:
> > On Mon, 15 Aug 2022 18:11:04 +0300
> > Yishai Hadas <yishaih@xxxxxxxxxx> wrote:
> >> +static int
> >> +vfio_ioctl_device_feature_logging_report(struct vfio_device *device,
> >> + u32 flags, void __user *arg,
> >> + size_t argsz)
> >> +{
> >> + size_t minsz =
> >> + offsetofend(struct vfio_device_feature_dma_logging_report,
> >> + bitmap);
> >> + struct vfio_device_feature_dma_logging_report report;
> >> + struct iova_bitmap_iter iter;
> >> + int ret;
> >> +
> >> + if (!device->log_ops)
> >> + return -ENOTTY;
> >> +
> >> + ret = vfio_check_feature(flags, argsz,
> >> + VFIO_DEVICE_FEATURE_GET,
> >> + sizeof(report));
> >> + if (ret != 1)
> >> + return ret;
> >> +
> >> + if (copy_from_user(&report, arg, minsz))
> >> + return -EFAULT;
> >> +
> >> + if (report.page_size < PAGE_SIZE || !is_power_of_2(report.page_size))
> >
> > Why is PAGE_SIZE a factor here? I'm under the impression that
> > iova_bitmap is intended to handle arbitrary page sizes. Thanks,
>
> Arbritary page sizes ... which are powers of 2. We use page shift in iova bitmap.
> While it's not hard to lose this restriction (trading a shift over a slower mul)
> ... I am not sure it is worth supporting said use considering that there aren't
> non-powers of 2 page sizes right now?
>
> The PAGE_SIZE restriction might be that it's supposed to be the lowest possible page_size.
Sorry, I was unclear. Size relative to PAGE_SIZE was my only question,
not that we shouldn't require power of 2 sizes. We're adding device
level dirty tracking, where the device page size granularity might be
4K on a host with a CPU 64K page size. Maybe there's a use case for
that. Given the flexibility claimed by the iova_bitmap support,
requiring reported page size less than system PAGE_SIZE seems
unjustified. Thanks,
Alex
> >> + return -EINVAL;
> >> +
> >> + ret = iova_bitmap_iter_init(&iter, report.iova, report.length,
> >> + report.page_size,
> >> + u64_to_user_ptr(report.bitmap));
> >> + if (ret)
> >> + return ret;
> >> +
> >> + for (; !iova_bitmap_iter_done(&iter) && !ret;
> >> + ret = iova_bitmap_iter_advance(&iter)) {
> >> + ret = device->log_ops->log_read_and_clear(device,
> >> + iova_bitmap_iova(&iter),
> >> + iova_bitmap_length(&iter), &iter.dirty);
> >> + if (ret)
> >> + break;
> >> + }
> >> +
> >> + iova_bitmap_iter_free(&iter);
> >> + return ret;
> >> +}
> >
>
