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SubjectRe: [RFCv2 05/16] x86/kvm: Make VirtIO use DMA API in KVM guest
On Tue, 20 Oct 2020 09:18:48 +0300
"Kirill A. Shutemov" <kirill@shutemov.name> wrote:

> VirtIO for KVM is a primary way to provide IO. All memory that used for
> communication with the host has to be marked as shared.
>
> The easiest way to archive that is to use DMA API that already knows how
> to deal with shared memory.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> drivers/virtio/virtio_ring.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index becc77697960..ace733845d5d 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 <xen/xen.h>
> +#include <asm/kvm_para.h>
>
> #ifdef DEBUG
> /* For development, we want to crash whenever the ring is screwed. */
> @@ -255,6 +256,9 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
> if (xen_domain())
> return true;
>
> + if (kvm_mem_protected())
> + return true;
> +

I guess it does not matter because Christophs comment, but this breaks
the build for s390, because there is no kvm_mem_protected() for s390.

Regards,
Halil

> return false;
> }
>

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