On Tue, Jul 19, 2022 at 10:02:56AM +0000, Keir Fraser wrote: > If virtio devices are tagged for "restricted-dma-pool", then that > pool should be used for virtio ring setup, via the DMA API. > > In particular, this fixes virtio_balloon for ARM PKVM, where the usual > workaround of setting VIRTIO_F_ACCESS_PLATFORM in the virtio device > doesn't work because the virtio_balloon driver clears the flag. This > seems a more robust fix than fiddling the flag again. > > Signed-off-by: Keir Fraser <keirf@xxxxxxxxxx> So the reason balloon disables ACCESS_PLATFORM is simply because it passes physical addresses to device and expects device to be able to poke at them. I worry about modifying DMA semantics yet again - it has as much of a chance to break some legacy configs as it has to fix some. And I don't really know much about restricted-dma-pool but I'd like to understand why does it make sense to set it for the balloon since it pokes at all and any system memory. > --- > drivers/virtio/virtio_ring.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index a5ec724c01d8..12be2607c648 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -12,6 +12,7 @@ > #include <linux/hrtimer.h> > #include <linux/dma-mapping.h> > #include <linux/spinlock.h> > +#include <linux/swiotlb.h> > #include <xen/xen.h> > > #ifdef DEBUG > @@ -248,6 +249,13 @@ static bool vring_use_dma_api(struct virtio_device *vdev) > if (!virtio_has_dma_quirk(vdev)) > return true; > > + /* If the device is configured to use a DMA restricted pool, > + * we had better use it. > + */ > + if (IS_ENABLED(CONFIG_DMA_RESTRICTED_POOL) && > + is_swiotlb_for_alloc(vdev->dev.parent)) > + return true; > + > /* Otherwise, we are left to guess. */ > /* > * In theory, it's possible to have a buggy QEMU-supposed > -- > 2.37.0.170.g444d1eabd0-goog _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
