Re: [Qemu-devel] [PATCH 1/2] ahci: Fix ahci cdrom read corruptions for reads > 128k

["Andreas Färber" <afaerber@suse.de>]

Hi Jason,

Am 26.07.2012 21:40, schrieb Jason Baron:
> While testing q35, which has its cdrom attached to the ahci controller, I found
> that the Fedora 17 install would panic on boot. The panic occurs while
> squashfs is trying to read from the cdrom. The errors are:
> 
> [    8.622711] SQUASHFS error: xz_dec_run error, data probably corrupt
> [    8.625180] SQUASHFS error: squashfs_read_data failed to read block
> 0x20be48a
> 
> I was also able to produce corrupt data reads using an installed piix based
> qemu machine, using 'dd'. I found that the corruptions were only occuring when
> the read size was greater than 128k. For example, the following command
> results in corrupted reads:
> 
> dd if=/dev/sr0 of=/tmp/blah bs=256k iflag=direct
> 
> The > 128k size reads exercise a different code path than 128k and below. In
> ide_atapi_cmd_read_dma_cb() s->io_buffer_size is capped at 128k. Thus,
> ide_atapi_cmd_read_dma_cb() is called a second time when the read is > 128k.
> However, ahci_dma_rw_buf() restart the read from offset 0, instead of at 128k.
> Thus, resulting in a corrupted read.
> 
> To fix this, I've introduced 'io_buffer_offset' field in IDEState to keep
> track of the offset. I've also modified ahci_populate_sglist() to take a new
> 3rd offset argument, so that the sglist is property initialized.
> 
> I've tested this patch using 'dd' testing, and Fedora 17 now correctly boots
> and installs on q35 with the cdrom ahci controller.
> 
> Signed-off-by: Jason Baron <jbaron@redhat.com>

Tested-by: Andreas Färber <afaerber@suse.de>

This also fixes my test case of running the "Check Installation Media"
boot menu option on, e.g., openSUSE-12.1-GNOME-LiveCD-x86_64.iso with
ich9-ahci (BNC#725008).

Thanks a lot for finding the root cause!

If you resubmit, please cc qemu-stable@nongnu.org, I would very much
like to backport this bugfix to stable-0.15 branch.

Regards,
Andreas

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