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Re: [Xen-devel] [PATCH 1/2] xen: arm64: doc: Add the requirement that SCR_EL3.HCE is enabled

On 20.04.2016 15:21, Julien Grall wrote:
(CC REST maintainers)

Hello Dirk,

Please CC the relevant maintainers for this patch. You can use
scripts/get_maintainers.pl for this purpose.

On 19/04/16 06:59, Dirk Behme wrote:
On ARM64 Linux the HVC instruction is used to trap into Xen. As this
can be set only at EL3, i.e. outside from Xen, document this boot

Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxxxxx>
  docs/misc/arm/booting.txt | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/docs/misc/arm/booting.txt b/docs/misc/arm/booting.txt
index 9802e5e..ffc9029 100644
--- a/docs/misc/arm/booting.txt
+++ b/docs/misc/arm/booting.txt
@@ -23,6 +23,10 @@ The exceptions to this on 32-bit ARM are as follows:

  There are no exception on 64-bit ARM.

+On ARM64 Linux it has to be ensured that the Secure Configuration
+Register has the HVC instructions enabled at EL1 and above
+(SCR_EL3.HCE == 1).

The requirement is the same for ARM32 (SCR.HCE == 1).

I would create a specific section in this documentation to list what the
firmware should do in EL3 before starting Xen.



In addition to this patch, I would add a check in Xen to make sure the
Hyp calls have been enabled by the firmware.

Hmm, I have to re-read the documentation how to do this in EL2. We can't read SCR_EL3 in EL2?

Best regards


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