linux-kernel - Re: [PATCH] virtio: Force DMA restricted devices through DMA API

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20220719074941-mutt-send-email-mst@kernel.org>
Date:   Tue, 19 Jul 2022 07:56:09 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Keir Fraser <keirf@...gle.com>
Cc:     Jason Wang <jasowang@...hat.com>, kernel-team@...roid.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio: Force DMA restricted devices through DMA API

On Tue, Jul 19, 2022 at 10:02:56AM +0000, Keir Fraser wrote:
> If virtio devices are tagged for "restricted-dma-pool", then that
> pool should be used for virtio ring setup, via the DMA API.
> 
> In particular, this fixes virtio_balloon for ARM PKVM, where the usual
> workaround of setting VIRTIO_F_ACCESS_PLATFORM in the virtio device
> doesn't work because the virtio_balloon driver clears the flag. This
> seems a more robust fix than fiddling the flag again.
> 
> Signed-off-by: Keir Fraser <keirf@...gle.com>


So the reason balloon disables ACCESS_PLATFORM is simply
because it passes physical addresses to device and
expects device to be able to poke at them.

I worry about modifying DMA semantics yet again - it has as much of a
chance to break some legacy configs as it has to fix some.


And I don't really know much about restricted-dma-pool but
I'd like to understand why does it make sense to set it for
the balloon since it pokes at all and any system memory.


> ---
>  drivers/virtio/virtio_ring.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index a5ec724c01d8..12be2607c648 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 <linux/spinlock.h>
> +#include <linux/swiotlb.h>
>  #include <xen/xen.h>
>  
>  #ifdef DEBUG
> @@ -248,6 +249,13 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
>  	if (!virtio_has_dma_quirk(vdev))
>  		return true;
>  
> +	/* If the device is configured to use a DMA restricted pool,
> +	 * we had better use it.
> +	 */
> +	if (IS_ENABLED(CONFIG_DMA_RESTRICTED_POOL) &&
> +	    is_swiotlb_for_alloc(vdev->dev.parent))
> +		return true;
> +
>  	/* Otherwise, we are left to guess. */
>  	/*
>  	 * In theory, it's possible to have a buggy QEMU-supposed
> -- 
> 2.37.0.170.g444d1eabd0-goog