linux-kernel - Re: possible dmar_init_reserved

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Message-ID: <20161223004801.GA1096@bhelgaas-glaptop.roam.corp.google.com>
Date:   Thu, 22 Dec 2016 18:48:01 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Raj, Ashok" <ashok.raj@...el.com>
Cc:     Joerg Roedel <joro@...tes.org>, linux-pci@...r.kernel.org,
        iommu@...ts.linux-foundation.org,
        David Woodhouse <dwmw2@...radead.org>,
        linux-kernel@...r.kernel.org, rwright@....com
Subject: Re: possible dmar_init_reserved_ranges() error

Hi Ashok,

On Thu, Dec 22, 2016 at 03:45:08PM -0800, Raj, Ashok wrote:
> Hi Bjorn
> 
> None in the platform group say they know about this. So i'm fairly sure
> we don't do that on Intel hardware (x86). 

I'm pretty sure there was once an x86 prototype for which PCI bus
addresses were not identical to CPU physical addresses, but I have no
idea whether it shipped that way.

Even if such a system never shipped, the x86 arch code supports _TRA,
and there's no reason to make the unnecessary assumption in this code
that _TRA is always zero.

If we didn't want to use pcibios_resource_to_bus() here for some
reason, we should at least add a comment about why we think it's OK to
use a CPU physical address as an IOVA.

Bjorn