linux-kernel - Re: [PATCH v5 04/12] iommu/vt-d: Add 256-bit invalidation descriptor support

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Date:   Wed, 5 Dec 2018 16:56:46 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     "Liu, Yi L" <yi.l.liu@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH v5 04/12] iommu/vt-d: Add 256-bit invalidation descriptor
 support

On Tue, Dec 04, 2018 at 02:13:31PM +0800, Lu Baolu wrote:
> The existing code uses GFP_ATOMIC, this patch only changes the size of
> the allocated desc_page.
> 
> I don't think we really need GFP_ATOMIC here (and also for some other
> places). I will clean up them in a separated patch.

Okay, thanks.

> > In this patch, there is some code like the code below. It calculates
> > destination address of memcpy with qi->desc. If it's still struct qi_desc
> > pointer, the calculation result would be wrong.
> > 
> > +			memcpy(desc, qi->desc + (wait_index << shift),
> > +			       1 << shift);
> > 
> > The change of the calculation method is to support 128 bits invalidation
> > descriptors and 256 invalidation descriptors in this unified code logic.
> > 
> > Also, the conversation between Baolu and me may help.
> > 
> > https://lore.kernel.org/patchwork/patch/1006756/
> 
> Yes. We need to support different descriptor size.

Okay, pointer arithmetic on void* isn't well defined in the C standard,
afaik. But it should work with GCC, so it's probably fine.

Unrelated to this patch-set, the whole qi management code needs some
cleanups, it queues a sync after every command and has very tricky
locking. This patch-set further complicates matters there, so it is
probably time for a clean re-write of that part?

Regards,

	Joerg