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

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Message-ID: <ede2e83b-0f8e-fa75-9905-ebed8b2ea980@gmail.com>
Date:   Mon, 5 Dec 2022 23:50:49 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Michael Kelley <mikelley@...rosoft.com>, kys@...rosoft.com,
        martin.petersen@...cle.com, longli@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, jejb@...ux.ibm.com,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org
Subject: Re: [PATCH 1/1] scsi: storvsc: Fix swiotlb bounce buffer leak in
 confidential VM



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@...rosoft.com>
Nice catch! Thanks to fix this.
Reviewed-by: Tianyu Lan <Tianyu.Lan@...rosoft.com>