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Re: [PATCH v4 1/7] docs/arm: Document Xen booting protocol on Armv8-R
- To: Julien Grall <julien@xxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Tue, 6 May 2025 12:24:48 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Tue, 06 May 2025 12:25:35 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH v4 1/7] docs/arm: Document Xen booting protocol on Armv8-R
Hi Julien,
> On 6 May 2025, at 12:44, Julien Grall <julien@xxxxxxx> wrote:
>
>
>
> On 29/04/2025 16:20, Luca Fancellu wrote:
>> Document the requirement needed to boot Xen on Armv8-R platforms.
>> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
>> ---
>> v4 changes:
>> - New patch
>> ---
>> docs/misc/arm/booting.txt | 8 ++++++++
>> 1 file changed, 8 insertions(+)
>> diff --git a/docs/misc/arm/booting.txt b/docs/misc/arm/booting.txt
>> index 21ae74837dcc..719af74f1e69 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 state is secure (S) on Arm64 and non secure (NS) on Arm32, hence
>> the
>> +above requirements need to be adjusted to this case:
> > +> +* Xen must be entered in S EL2 mode on Arm64 and in NS EL2 mode on
> > Arm32.
>
> I think it would be better to update the line "Xen must be entered in NS EL2
> mode" to clarify the state for 64-bit Arm.
>
> > +> +* Xen must be entered with MPU off and data cache disabled (SCTLR_EL2.M
> > bit and
>> + SCTLR_EL2.C set to 0).
>
> This line is valid for Armv8-A/Armv7-A when using the Image/zImage protocol.
>
>> [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
Just to be sure to be on the same page, are you suggesting these changes on the
original file?
diff --git a/docs/misc/arm/booting.txt b/docs/misc/arm/booting.txt
index 21ae74837dcc..c00c651805d7 100644
--- a/docs/misc/arm/booting.txt
+++ b/docs/misc/arm/booting.txt
@@ -58,10 +58,14 @@ Firmware/bootloader requirements
Xen relies on some settings the firmware has to configure in EL3 before
starting Xen.
-* Xen must be entered in NS EL2 mode
+* Xen must be entered in:
+ * Non-Secure EL2 mode for Armv8-A Arm64 and Arm32, Armv8-R Arm32.
+ * Secure EL2 mode for Armv8-R Arm64.
* The bit SCR_EL3.HCE (resp. SCR.HCE for 32-bit ARM) must be set to 1.
+* Xen must be entered with MMU/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
Cheers,
Luca
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