linux-kernel - Re: [PATCH 4/4] kvm/vfio: Support for DMA coherent IOMMUs

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Date:	Tue, 18 Feb 2014 11:38:32 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>, kvm@...r.kernel.org
CC:	Gleb Natapov <gleb@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] kvm/vfio: Support for DMA coherent IOMMUs

Il 17/02/2014 21:24, Alex Williamson ha scritto:
> VFIO now has support for using the IOMMU_CACHE flag and a mechanism
> for an external user to test the current operating mode of the IOMMU.
> Add support for this to the kvm-vfio pseudo device so that we only
> register noncoherent DMA when necessary.
>
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> Cc: Gleb Natapov <gleb@...nel.org>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  virt/kvm/vfio.c |   27 ++++++++++++++++++++-------
>  1 file changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> index b4f9507..ba1a93f 100644
> --- a/virt/kvm/vfio.c
> +++ b/virt/kvm/vfio.c
> @@ -59,6 +59,22 @@ static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
>  	symbol_put(vfio_group_put_external_user);
>  }
>
> +static bool kvm_vfio_group_is_coherent(struct vfio_group *vfio_group)
> +{
> +	long (*fn)(struct vfio_group *, unsigned long);
> +	long ret;
> +
> +	fn = symbol_get(vfio_external_check_extension);
> +	if (!fn)
> +		return false;
> +
> +	ret = fn(vfio_group, VFIO_DMA_CC_IOMMU);
> +
> +	symbol_put(vfio_external_check_extension);
> +
> +	return ret > 0;
> +}
> +
>  /*
>   * Groups can use the same or different IOMMU domains.  If the same then
>   * adding a new group may change the coherency of groups we've previously
> @@ -75,13 +91,10 @@ static void kvm_vfio_update_coherency(struct kvm_device *dev)
>  	mutex_lock(&kv->lock);
>
>  	list_for_each_entry(kvg, &kv->group_list, node) {
> -		/*
> -		 * TODO: We need an interface to check the coherency of
> -		 * the IOMMU domain this group is using.  For now, assume
> -		 * it's always noncoherent.
> -		 */
> -		noncoherent = true;
> -		break;
> +		if (!kvm_vfio_group_is_coherent(kvg->vfio_group)) {
> +			noncoherent = true;
> +			break;
> +		}
>  	}
>
>  	if (noncoherent != kv->noncoherent) {
>

Acked-by: Paolo Bonzini <pbonzini@...hat.com>
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