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Re: [PATCH 0/3] x86/pvh: Support relocating dom0 kernel
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 7 Mar 2024 11:08:37 +0100
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Thu, 07 Mar 2024 10:08:47 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 07.03.2024 11:00, Roger Pau Monné wrote:
> On Wed, Mar 06, 2024 at 01:50:29PM -0500, Jason Andryuk wrote:
>> Xen tries to load a PVH dom0 kernel at the fixed guest physical address
>> from the elf headers. For Linux, this defaults to 0x1000000 (16MB), but
>> it can be configured.
>>
>> Unfortunately there exist firmwares that have reserved regions at this
>> address, so Xen fails to load the dom0 kernel since it's not RAM.
>>
>> The other issue is that the Linux PVH entry point is not
>> position-independent. It expects to run at the compiled
>> CONFIG_PHYSICAL_ADDRESS.
>>
>> This patch set expands the PVH dom0 builder to try to relocate the
>> kernel if needed and possible. XENFEAT_pvh_relocatable is added for
>> kernels to indicate they are relocatable. However, we may want to
>> switch to an additional ELF note with the kernel alignment. Linux
>> specifies a kernel alignment in the bzImage boot_params.setup_header,
>> but that is not present the ELF vmlinux file.
>
> I wonder whether we need a pair of notes, to signal the min/max
> addresses the kernel supports being relocated to.
Plus, as per your other reply, a 3rd one to specify alignment needs.
Then again - a single note can have multiple values. So perhaps it
doesn't need to be more than one new notes (except if dealing with
multi-value ones is deemed too complicated).
Jan
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