Re: [PATCH 1/1] scsi: storvsc: Fix swiotlb bounce buffer leak in confidential VM

[Tianyu Lan <ltykernel@gmail.com>]

On 12/5/2022 3:52 AM, Michael Kelley wrote:
> storvsc_queuecommand() maps the scatter/gather list using scsi_dma_map(),
> which in a confidential VM allocates swiotlb bounce buffers. If the
> I/O submission fails in storvsc_do_io(), the I/O is typically retried
> by higher level code, but the bounce buffer memory is never freed.
> The mostly like cause of I/O submission failure is a full VMBus
> channel ring buffer, which is not uncommon under high I/O loads.
> Eventually enough bounce buffer memory leaks that the confidential
> VM can't do any I/O. The same problem can arise in a non-confidential
> VM with kernel boot parameter swiotlb=force.
> 
> Fix this by doing scsi_dma_unmap() in the case of an I/O submission
> error, which frees the bounce buffer memory.
> 
> Fixes: 743b237c3a7b ("scsi: storvsc: Add Isolation VM support for storvsc driver")
> Signed-off-by: Michael Kelley<mikelley@microsoft.com>
Nice catch! Thanks to fix this.
Reviewed-by: Tianyu Lan <Tianyu.Lan@microsoft.com>