linux-kernel - Re: [PATCH v1 1/4] iommu/tegra: gart: Add debugging facility

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Message-ID: <20180427094612.GM30388@ulmo>
Date:   Fri, 27 Apr 2018 11:46:12 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/4] iommu/tegra: gart: Add debugging facility

On Mon, Apr 09, 2018 at 11:07:19PM +0300, Dmitry Osipenko wrote:
> Page mapping could overwritten by an accident (a bug). We can catch this
> case by checking 'VALID' bit of GART's page entry prior to mapping of a
> page. Since that check introduces a small performance impact, it should be
> enabled explicitly using new GART's kernel module 'debug' parameter.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/iommu/tegra-gart.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)

I think this was discussed before, but this really shouldn't be needed
unless the IOVA allocator or GART driver are buggy.

That said, I think this has some usefulness to find such bugs, so:

Acked-by: Thierry Reding <treding@...dia.com>

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