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

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Message-ID: <20120725104138.GA11098@stefanha-thinkpad.localdomain>
Date:	Wed, 25 Jul 2012 11:41:38 +0100
From:	Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Wang Sen <senwang@...ux.vnet.ibm.com>, linux-scsi@...r.kernel.org,
	JBottomley@...allels.com, mc@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: virtio-scsi: Fix address translation failure of
 HighMem pages used by sg list

On Wed, Jul 25, 2012 at 10:44:14AM +0200, Paolo Bonzini wrote:
> Il 25/07/2012 10:29, 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 there are some HighMem pages in 
> > table->sgl 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.
> 
> Heh, I was compiling (almost) the same patch as we speak. :)
> 
> I've never seen QEMU crash; the VM would more likely just fail to boot
> with a panic.  But it's the same bug anyway.

It's not a segfault "crash", I think it hits an abort(3) in QEMU's
virtio code when trying to map an invalid guest physical address.

Stefan

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