linux-kernel - Re: [PATCH] iommu/amd: flush not present cache in iommu_map

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Message-ID: <20190424145819.GA16141@infradead.org>
Date:   Wed, 24 Apr 2019 07:58:19 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Tom Murphy <tmurphy@...sta.com>, Joerg Roedel <joro@...tes.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Tom Murphy <murphyt7@....ie>
Subject: Re: [PATCH] iommu/amd: flush not present cache in iommu_map_page

On Wed, Apr 24, 2019 at 03:47:39PM +0100, Tom Murphy wrote:
> >And I'd really like to understand the unlikely - amd_iommu_np_cache
> >is set based on a hardware capability, so it seems rather odd to mark
> >it unlikely.  Dynamic branch prediction really should do the right thing
> >here usually.
> 
> Here is the commit which added it without any explanation:
> https://github.com/torvalds/linux/commit/270cab2426cdc6307725e4f1f46ecf8ab8e69193
> 
> should we remove it seen as there's no explanation given ?

I'd be tempted to do that.  But lets just ask Joerg if he has
any opinion..