Re: [PATCH] scsi: virtio-scsi: Fix address translation failure ofHighMem pages used by sg list

[Sen Wang]

2012/7/25 Paolo Bonzini <pbonzini@xxxxxxxxxx>:
> 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. :)

Uh, what a coincidence! :)

>
> 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.

I never met this before. How this situation happens?

>
>> My solution is using sg_set_page instead of sg_set_buf.
>>
>> I have tested the patch on my workstation. QEMU would not crash any more.
>>
>> Signed-off-by: Wang Sen <senwang@xxxxxxxxxxxxxxxxxx>
>> ---
>>  drivers/scsi/virtio_scsi.c |    3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
>> index 1b38431..fc5c88a 100644
>> --- a/drivers/scsi/virtio_scsi.c
>> +++ b/drivers/scsi/virtio_scsi.c
>> @@ -198,7 +198,8 @@ static void virtscsi_map_sgl(struct scatterlist *sg, unsigned int *p_idx,
>>       int i;
>>
>>       for_each_sg(table->sgl, sg_elem, table->nents, i)
>> -             sg_set_buf(&sg[idx++], sg_virt(sg_elem), sg_elem->length);
>> +             sg_set_page(&sg[idx++], sg_page(sg_elem), sg_elem->length,
>> +                     sg_elem->offset);
>
> This can simply be
>
>    sg[idx++] = *sg_elem;
>

Yes, I saw your another E-mail. I think you're right. Simply calling
sg_set_page can not handle
the flag bits correctly. So, I'll repost the patch soon. Thank you!

> Can you repost it with this change, and also add stable@xxxxxxxxxxxxxxx
> to the Cc?  Thanks very much!
>
> Paolo
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Wang Sen
Addr: XUPT,Xi'an,Shaanxi,China
Email: kelvin.xupt@xxxxxxxxx
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