linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Leave scalable mode default off

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Message-ID: <20190124132250.k3rnlpaqazmatzaf@8bytes.org>
Date:   Thu, 24 Jan 2019 14:22:50 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     David Woodhouse <dwmw2@...radead.org>, ashok.raj@...el.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH 1/1] iommu/vt-d: Leave scalable mode default off

On Thu, Jan 24, 2019 at 10:31:32AM +0800, Lu Baolu wrote:
> Commit 765b6a98c1de3 ("iommu/vt-d: Enumerate the scalable
> mode capability") enables VT-d scalable mode if hardware
> advertises the capability. As we will bring up different
> features and use cases to upstream in different patch
> series, it will leave some intermediate kernel versions
> which support partial features. Hence, end user might run
> into problems when they use such kernels on bare metals
> or virtualization environments.

I don't get it, can you be more specific about the problems that users
might run into? And is this patch needed as a fix for v5.0 or is it just
a precaution because future patches might break something for users?


Regards,

	Joerg