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    SubjectRe: [PATCH v2 05/20] virtio: Implement get_shm_region for MMIO transport
    On Fri, Aug 07, 2020 at 03:55:11PM -0400, Vivek Goyal wrote:
    > From: Sebastien Boeuf <sebastien.boeuf@intel.com>
    >
    > On MMIO a new set of registers is defined for finding SHM
    > regions. Add their definitions and use them to find the region.
    >
    > Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
    > Cc: kvm@vger.kernel.org
    > Cc: "Michael S. Tsirkin" <mst@redhat.com>


    Acked-by: Michael S. Tsirkin <mst@redhat.com>

    > ---
    > drivers/virtio/virtio_mmio.c | 32 ++++++++++++++++++++++++++++++++
    > include/uapi/linux/virtio_mmio.h | 11 +++++++++++
    > 2 files changed, 43 insertions(+)
    >
    > diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
    > index 627ac0487494..2697c492cf78 100644
    > --- a/drivers/virtio/virtio_mmio.c
    > +++ b/drivers/virtio/virtio_mmio.c
    > @@ -498,6 +498,37 @@ static const char *vm_bus_name(struct virtio_device *vdev)
    > return vm_dev->pdev->name;
    > }
    >
    > +static bool vm_get_shm_region(struct virtio_device *vdev,
    > + struct virtio_shm_region *region, u8 id)
    > +{
    > + struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
    > + u64 len, addr;
    > +
    > + /* Select the region we're interested in */
    > + writel(id, vm_dev->base + VIRTIO_MMIO_SHM_SEL);
    > +
    > + /* Read the region size */
    > + len = (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_LEN_LOW);
    > + len |= (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_LEN_HIGH) << 32;
    > +
    > + region->len = len;
    > +
    > + /* Check if region length is -1. If that's the case, the shared memory
    > + * region does not exist and there is no need to proceed further.
    > + */
    > + if (len == ~(u64)0) {
    > + return false;
    > + }
    > +

    It might make sense to validate that addr/len do not overlap.
    Will be useful for PCI too.
    Can be a patch on top.

    > + /* Read the region base address */
    > + addr = (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_BASE_LOW);
    > + addr |= (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_BASE_HIGH) << 32;
    > +
    > + region->addr = addr;
    > +
    > + return true;
    > +}
    > +
    > static const struct virtio_config_ops virtio_mmio_config_ops = {
    > .get = vm_get,
    > .set = vm_set,
    > @@ -510,6 +541,7 @@ static const struct virtio_config_ops virtio_mmio_config_ops = {
    > .get_features = vm_get_features,
    > .finalize_features = vm_finalize_features,
    > .bus_name = vm_bus_name,
    > + .get_shm_region = vm_get_shm_region,
    > };
    >
    >
    > diff --git a/include/uapi/linux/virtio_mmio.h b/include/uapi/linux/virtio_mmio.h
    > index c4b09689ab64..0650f91bea6c 100644
    > --- a/include/uapi/linux/virtio_mmio.h
    > +++ b/include/uapi/linux/virtio_mmio.h
    > @@ -122,6 +122,17 @@
    > #define VIRTIO_MMIO_QUEUE_USED_LOW 0x0a0
    > #define VIRTIO_MMIO_QUEUE_USED_HIGH 0x0a4
    >
    > +/* Shared memory region id */
    > +#define VIRTIO_MMIO_SHM_SEL 0x0ac
    > +
    > +/* Shared memory region length, 64 bits in two halves */
    > +#define VIRTIO_MMIO_SHM_LEN_LOW 0x0b0
    > +#define VIRTIO_MMIO_SHM_LEN_HIGH 0x0b4
    > +
    > +/* Shared memory region base address, 64 bits in two halves */
    > +#define VIRTIO_MMIO_SHM_BASE_LOW 0x0b8
    > +#define VIRTIO_MMIO_SHM_BASE_HIGH 0x0bc
    > +
    > /* Configuration atomicity value */
    > #define VIRTIO_MMIO_CONFIG_GENERATION 0x0fc
    >
    > --
    > 2.25.4
    >

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