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Xen Armv8-R booting protocol
- To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Tue, 15 Apr 2025 12:10:24 +0000
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- Cc: 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 12:11:12 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-index: AQHbrf9e2Q3ZtL+0AUaAx8EjnSV7Wg==
- Thread-topic: Xen Armv8-R booting protocol
Hi all,
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”.
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.
+
+* 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.
Cheers,
Luca
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