From: Gerd Hoffmann <kraxel@redhat.com>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: qemu-devel@nongnu.org, qemu-stable@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] usb: Fix usb_packet_map() in the presence of IOMMUs
Date: Wed, 26 Sep 2012 08:32:26 +0200 [thread overview]
Message-ID: <5062A17A.9070401@redhat.com> (raw)
In-Reply-To: <1348628371-6828-1-git-send-email-david@gibson.dropbear.id.au>
On 09/26/12 04:59, David Gibson wrote:
> With the IOMMU infrastructure introduced before 1.2, we need to use
> dma_memory_map() to obtain a qemu pointer to memory from an IO bus address.
> However, dma_memory_map() alters the given length to reflect the length
> over which the used DMA translation is valid - which could be either more
> or less than the requested length.
>
> usb_packet_map() does not correctly handle these cases, simply failing if
> dma_memory_map() alters the requested length. If dma_memory_map()
> increased the length, we just need to use the requested length for the
> qemu_iovec_add(). However, if it decreased the length, it means that a
> single DMA translation is not valid for the whole sglist element, and so
> we need to loop, splitting it up into multiple iovec entries for each
> piece with a DMA translation (in practice >2 pieces is unlikely).
>
> This patch implements the correct behaviour
Patch added to usb patch queue.
thanks,
Gerd
prev parent reply other threads:[~2012-09-26 6:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-26 2:59 [Qemu-devel] [PATCH] usb: Fix usb_packet_map() in the presence of IOMMUs David Gibson
2012-09-26 6:32 ` Gerd Hoffmann [this message]
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