linux-kernel - Re: [RFCv2 05/16] x86/kvm: Make VirtIO use DMA API in KVM guest

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Date:   Thu, 22 Oct 2020 05:31:18 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        David Rientjes <rientjes@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Will Drewry <wad@...omium.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        Liran Alon <liran.alon@...cle.com>,
        Mike Rapoport <rppt@...nel.org>, x86@...nel.org,
        kvm@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [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@...temov.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@...ux.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;
>  }
>