Re: [boot-wrapper v4 4/4] aarch64: Start Xen on Armv8-R at EL2

[Luca Fancellu <Luca.Fancellu@arm.com>]

Hi Mark,

> On 26 Nov 2024, at 11:58, Mark Rutland <mark.rutland@arm.com> wrote:
> 
> On Thu, Oct 17, 2024 at 10:55:20AM +0100, Luca Fancellu wrote:
>> When bootwrapper is compiled with Xen support and it is started
>> at EL2 on Armv8-R AArch64, keep the current EL and jump to the
>> Xen image using the SPSR_KERNEL as spsr_el2 value.
> 
> What's the plan for booting Xen? i.e. is that using spin-table or PSCI?
> 
> I'm hesitant to expose PSCI booting to EL2 on ARMv8-R, because PSCI
> doesn't really support ARMv8-R (the spec says nothing about it, and all
> we're doing is providing the illusion of ARMv8-A to Linux), and Xen
> would have to override the vectors anyway, so it doesn't really make
> sense.
> 
> Given the latter part I'm assuming you only care about spin-table for
> Xen, which is less concerning. I think we should make that more explicit
> in the config options and forbid the combination of ARMv8-R + PSCI +
> Xen.

Yes, I only care about spin-table at the moment, would this diff on top of this
patch be ok for you in order to enforce that?

diff --git a/configure.ac b/configure.ac
index a433c89bd2ae..a16bc25508f3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -115,6 +115,11 @@ AS_IF([test "x$USE_PSCI" != "xyes" -a "x$KERNEL_ES" = "x32"],
        [AC_MSG_ERROR([With an AArch32 kernel, boot method must be PSCI.])]
 )
 
+# Don't allow PSCI + Xen + aarch64-r
+AS_IF([test "x$USE_PSCI" = "xyes" -a "x$USE_ARCH" = "xaarch64-r" -a "x$X_IMAGE" != "x"],
+       [AC_MSG_ERROR([With aarch64-r and Xen, PSCI must be disabled.])]
+)
+
 # Allow a user to pass --with-initrd
 AC_ARG_WITH([initrd],
        AS_HELP_STRING([--with-initrd], [embed an initrd in the kernel image]),

Cheers,
Luca