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[RFCv2,05/16] x86/kvm: Make VirtIO use DMA API in KVM guest

Message ID 20201020061859.18385-6-kirill.shutemov@linux.intel.com
State New
Headers show
Series KVM protected memory extension | expand

Commit Message

Kirill A. Shutemov Oct. 20, 2020, 6:18 a.m. UTC
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(+)

Comments

Christoph Hellwig Oct. 20, 2020, 8:06 a.m. UTC | #1
NAK.  Any virtio implementation that needs special DMA OPS treatment
needs to set the VIRTIO_F_ACCESS_PLATFORM bit.  The only reason the
Xen hack existst is because it slipped in a long time ago and we can't
fix that any more.
Kirill A. Shutemov Oct. 20, 2020, 12:47 p.m. UTC | #2
On Tue, Oct 20, 2020 at 09:06:58AM +0100, Christoph Hellwig wrote:
> NAK.  Any virtio implementation that needs special DMA OPS treatment
> needs to set the VIRTIO_F_ACCESS_PLATFORM bit.  The only reason the
> Xen hack existst is because it slipped in a long time ago and we can't
> fix that any more.

Thanks. Will fix.
Halil Pasic Oct. 22, 2020, 3:31 a.m. UTC | #3
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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Patch

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;
+
 	return false;
 }