Re: [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit

[Paolo Bonzini <pbonzini@redhat.com>]

On 05/09/2016 13:13, P J P wrote:
> +-- On Mon, 5 Sep 2016, Paolo Bonzini wrote --+
> | No, that's not what happens.  chunk_size is set to sg.resid, after which:
> | 
> |         sg.dataAddr += chunk_size;
> |         data_length -= chunk_size;
> |         sg.resid -= chunk_size;
> | 
> | The loop is reentered with sg.resid == 0, it calls into
> | pvscsi_get_next_sg_elem and this sets sg.resid to a nonzero value.  It's
> | not an infinite loop.
> 
>   Yes, true; But 'pvscsi_get_next_sg_elem' does not return non-zero 'sg.resid' 
> each time. In fact, it returns more zeros and thus the loop iterates 
> infinitely. When I ran it with 64 bit 'data_length' and without cast, after 
> some time, the inner loop gets stuck and does not seem to read non-zero values 
> into 'sg.resid'.

pvscsi_get_next_sg_elem just reads 16 bytes from guest RAM, so I guess
that's because you didn't set up the SG list correctly.  QEMU indeed
doesn't check for that, but that's a different bug.

> Is there limit to number of SG elements?

Without a public spec it's hard, but I guess 2048 is more than enough.

Paolo