linux-kernel - Re: [PATCH v3] scsi: virtio-scsi: Fix address translation failure of HighMem pages used by sg list

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Message-ID: <50163B9D.9040409@redhat.com>
Date:	Mon, 30 Jul 2012 09:45:33 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Wang Sen <senwang@...ux.vnet.ibm.com>
CC:	JBottomley@...allels.com, bharrosh@...asas.com,
	stefanha@...ux.vnet.ibm.com, mc@...ux.vnet.ibm.com,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	zwanp@...ibm.com, xiaoguangrong@...ux.vnet.ibm.com
Subject: Re: [PATCH v3] scsi: virtio-scsi: Fix address translation failure
 of HighMem pages used by sg list

Il 30/07/2012 08:25, Wang Sen ha scritto:
> When using the commands below to write some data to a virtio-scsi LUN of the
> QEMU guest(32-bit) with 1G physical memory(qemu -m 1024), the qemu will crash.
> 
>         # sudo mkfs.ext4 /dev/sdb  (/dev/sdb is the virtio-scsi LUN.)
>         # sudo mount /dev/sdb /mnt
>         # dd if=/dev/zero of=/mnt/file bs=1M count=1024
> 
> In current implementation, sg_set_buf is called to add buffers to sg list which
> is put into the virtqueue eventually. But if there are some HighMem pages in
> table->sgl you can not get virtual address by sg_virt. So, sg_virt(sg_elem) may
> return NULL value. This will cause QEMU exit when virtqueue_map_sg is called
> in QEMU because an invalid GPA is passed by virtqueue.
> 
> Two solutions are discussed here:
> http://lkml.indiana.edu/hypermail/linux/kernel/1207.3/00675.html
> 
> Finally, value assignment approach was adopted because:
> 
> Value assignment creates a well-formed scatterlist, because the termination 
> marker in source sg_list has been set in blk_rq_map_sg(). The last entry of the
> source sg_list is just copied to the the last entry in destination list.  Note 
> that, for now, virtio_ring does not care about the form of the scatterlist and 
> simply processes the first out_num + in_num consecutive elements of the sg[] 
> array.
> 
> I have tested the patch on my workstation. QEMU would not crash any more.
> 
> Cc: <stable@...r.kernel.org> # 3.4: 4fe74b1: [SCSI] virtio-scsi: SCSI driver
> Signed-off-by: Wang Sen <senwang@...ux.vnet.ibm.com>

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

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