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Date: Fri, 6 Jan 2023 16:32:18 +0100
From: "Gerd Hoffmann" <kraxel@redhat.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: devel@edk2.groups.io, Ard Biesheuvel <ardb+tianocore@kernel.org>,
	=?utf-8?B?TMOhc3psw7Mgw4lyc2Vr?= <lersek@redhat.com>,
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	Pawel Polawski <ppolawsk@redhat.com>,
	Oliver Steffen <osteffen@redhat.com>,
	Jiewen Yao <jiewen.yao@intel.com>
Subject: Re: [PATCH 0/2] OvmfPkg: check 64bit mmio window for resource conflicts
Message-ID: <20230106153218.uxvl6vttwes4k4mh@sirius.home.kraxel.org>
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On Fri, Jan 06, 2023 at 03:14:53PM +0100, Ard Biesheuvel wrote:
> Hi Gerd,
> 
> On Fri, 6 Jan 2023 at 15:04, Gerd Hoffmann <kraxel@redhat.com> wrote:
> >
> >
> >
> > Gerd Hoffmann (2):
> >   OvmfPkg/PlatformInitLib: update PlatformScanOrAdd64BitE820Ram
> >     documentation
> >   OvmfPkg/PlatformInitLib: check 64bit mmio window for resource
> >     conflicts
> >
> >  OvmfPkg/Library/PlatformInitLib/MemDetect.c | 63 +++++++++++++++++----
> >  1 file changed, 51 insertions(+), 12 deletions(-)
> >
> 
> Mind adding a teeny bit of context to explain why this is needed? No
> need to respin or anything - just want to make sure i understand the
> problem and the solution.

qemu reserves some address space below 1TB when emulating amd processors
because that is the address range used by the amd iommu.  This avoids
placing the mmio window at a overlapping range.

https://bugzilla.tianocore.org/show_bug.cgi?id=4251

(guess I should add a link to the commit message ...)

take care,
  Gerd