linux-kernel - Re: [PATCH v5] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests.

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Message-ID: <20201119075422.GA15840@lst.de>
Date:   Thu, 19 Nov 2020 08:54:22 +0100
From:   Christoph Hellwig <hch@....de>
To:     Ashish Kalra <Ashish.Kalra@....com>
Cc:     konrad.wilk@...cle.com, hch@....de, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, x86@...nel.org,
        luto@...nel.org, peterz@...radead.org, dave.hansen@...ux-intel.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        brijesh.singh@....com, Thomas.Lendacky@....com, jon.grimm@....com,
        rientjes@...gle.com
Subject: Re: [PATCH v5] swiotlb: Adjust SWIOTBL bounce buffer size for SEV
 guests.

On Wed, Nov 18, 2020 at 08:12:43PM +0000, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
> 
> For SEV, all DMA to and from guest has to use shared
> (un-encrypted) pages. SEV uses SWIOTLB to make this
> happen without requiring changes to device drivers.
> However, depending on workload being run, the default
> 64MB of SWIOTLB might not be enough and SWIOTLB
> may run out of buffers to use for DMA, resulting
> in I/O errors and/or performance degradation for
> high I/O workloads.

FYI, you can use up 73 chars for your commit log.  This looks rather
compressed.