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From: John Snow <jsnow@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] ahci: map memory via device's address
 space instead of address_space_memory
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To: Jordan Hargrave <jharg93@gmail.com>
Cc: qemu-devel <qemu-devel@nongnu.org>



On 03/02/2015 11:03 AM, Jordan Hargrave wrote:
>
>
> On Thu, Feb 26, 2015 at 4:31 PM, John Snow <jsnow@redhat.com
> <mailto:jsnow@redhat.com>> wrote:
>
>     (Please don't top-post on qemu-devel: gmail is kind of awful about
>     this, but if you expand the conversation while in-reply, you can
>     edit beneath the quote instead of above.)
>
>     On 02/26/2015 04:31 PM, Jordan Hargrave wrote:
>
>         The problem is the FIS registers have stale data.
>
>         SeaBIOS initialization leaves the registers:
>         PORT_FIS_ADDR = 0x7fae0000
>         PORT_FIS_ADDR_HI = 0x0
>
>         My OS initializes DMAR page tables and then enables the IOMMU
>         translation.
>         Then OS initializes AHCI driver.  Writes VIRTUAL DMA to FIS
>         registers.
>         eg. FIS DMA address is 0x10000 (maps to some hardware physical
>         address
>         via iommu)
>
>         The OS writes 0x00 PORT_FIS_ADDR_HI -> qemu calls map_page (0x00
>         << 32)
>         | 0x7fae0000... 0x7fae0000 is stale, and is not in the IOMMU
>         page map.
>         Causes a non-recoverable IOMMU fault.
>
>
>
>     OK, I see.
>
>     We can probably fix this by delaying the map and having it map
>     on-demand before first access, setting a dirty flag if the registers
>     have changed since last use.
>
>     It might be an AHCI spec violation to change this register once the
>     FIS Receive Engine is active, too, so it might not be too hard of a
>     change; perhaps we can just map the FIS Receive Buffer once the FRE
>     is started.
>
>     Did you want to send a patch, or should I?
>
>     --js
>
>
> I'm not as familiar with qemu internals yet to figure out how to map the
> memory on demand.   I switched order of FIS initialization in my OS
> driver for the time being.  The same problem was happening with the
> PORT_ADDR_LST/PORT_ADDR_LST_HI register initialization pwas well.

Okay, I'll pick this up, then. Thanks!