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Re: Xen Armv8-R booting protocol
- To: Ayan Kumar Halder <ayankuma@xxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Tue, 15 Apr 2025 13:10:25 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Julien Grall <julien@xxxxxxx>, "Orzel, Michal" <michal.orzel@xxxxxxx>, Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
- Delivery-date: Tue, 15 Apr 2025 13:11:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Nodisclaimer: true
- Thread-index: AQHbrf9eNLQ3I8ChLUu7y92fKMnf87OksnaAgAAA54A=
- Thread-topic: Xen Armv8-R booting protocol
Hi Ayan,
> On 15 Apr 2025, at 14:06, Ayan Kumar Halder <ayankuma@xxxxxxx> wrote:
>
>
> On 15/04/2025 13:10, Luca Fancellu wrote:
>> Hi all,
> Hi Luca,
>>
>> I’ve started this thread to talk about a possible Xen booting protocol when
>> running on Armv8-R,
>> currently Xen uses the Linux boot protocol and some other requirements
>> stated in docs/misc/arm/booting.txt.
>>
>> Unfortunately we don’t have anything already available for Armv8-R, the only
>> implementation of a bootloader
>> is the boot-wrapper-aarch64 which keeps the MPU off, I/D cache off.
>>
>> So my proposal is to add additional requirements in our
>> docs/misc/arm/booting.txt for the case where Xen is
>> started on Armv8-R, under "Firmware/bootloader requirements”.
> This makes sense.
>>
>> diff --git a/docs/misc/arm/booting.txt b/docs/misc/arm/booting.txt
>> index 21ae74837dcc..39f029153e38 100644
>> --- a/docs/misc/arm/booting.txt
>> +++ b/docs/misc/arm/booting.txt
>> @@ -62,6 +62,14 @@ Xen relies on some settings the firmware has to configure
>> in EL3 before starting
>> * The bit SCR_EL3.HCE (resp. SCR.HCE for 32-bit ARM) must be set to 1.
>> +When Xen runs on Armv8-R, the highest exception level is EL2 and the only
>> +available mode is secure, hence the above requirements needs to be adjusted
>> to
>> +this case:
>> +
>> +* Xen must be entered in S EL2 mode.
>
> Refer ARM DDI 0568A.c ID110520 A1.3.1
>
> Armv8-R (AArch32) only supports a single Security state, Non-secure.
>
> I see that it differs from Armv8-R (AArch64) ARM DDI 0600A.d ID120821, A1.3
>
> The PE is always in Secure state.
>
> Probably you can mention both.
ok, then it should be S/NS EL2.
>
>> +
>> +* Xen must be entered with MPU off and data cache disabled (SCTLR_EL2.M bit
>> and
>> + SCTLR_EL2.C set to 0).
>> [1] linux/Documentation/arm/booting.rst
>> Latest version:
>> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arch/arm/booting.rst
>>
>> Please let me know your thoughts.
>
> A question, Do you know if u-boot (or any other bootloader) is supported on
> Armv8-R ? Because someone needs to pass the DTB address in r2/x0.
As far as I know, no other boot loader is supported, we had patches for u-boot
enabling MPU at EL2 but they were not merged.
I’m currently building Xen with the device tree embedded.
Cheers,
Luca
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