[boot-wrapper 7/7] aarch64: Start Xen on Armv8-R at EL2

[Andre Przywara]

On Thu,  6 Jun 2024 14:36:28 +0100
Luca Fancellu <luca.fancellu at arm.com> wrote:

Hi,

> 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.
> 
> Additionally, don't permit the usage of hvc conduit when Xen
> kernel is passed, because it's not supported.

Mmh, but this is unrelated to v8R, isn't it?
And I am not sure there is too much merit in checking this here?
After all PSCI *could* be triggered like this from EL2 (to EL2) in the
future, even if the *current* Xen implementation does not support this.

> Signed-off-by: Luca Fancellu <luca.fancellu at arm.com>
> ---
>  Makefile.am         | 1 +
>  arch/aarch64/boot.S | 7 +++++++
>  configure.ac        | 3 +++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/Makefile.am b/Makefile.am
> index 34fbfb1f4ff8..bafce34682c3 100644
> --- a/Makefile.am
> +++ b/Makefile.am
> @@ -112,6 +112,7 @@ XEN_CHOSEN	:= xen,xen-bootargs = \"$(XEN_CMDLINE)\";		\
>  			compatible = \"xen,linux-zimage\", \"xen,multiboot-module\"; \
>  			reg = <0x0 $(DOM0_OFFSET) 0x0 $(KERNEL_SIZE)>;	\
>  		   };
> +DEFINES		+= -DXEN
>  endif
>  
>  if INITRD
> diff --git a/arch/aarch64/boot.S b/arch/aarch64/boot.S
> index b2b9863b8d6a..0b30b82ad6d9 100644
> --- a/arch/aarch64/boot.S
> +++ b/arch/aarch64/boot.S
> @@ -88,6 +88,7 @@ reset_at_el2:
>  	cmp	x0, 0xf
>  	bne	reset_no_el3
>  
> +#if !defined(XEN)
>  	/*
>  	 * Armv8-R AArch64 is found, check if Linux can be booted.

Does Xen equally rely on VMSA in EL1? Or does it not care, and just
leaves the EL1 setup totally to the guest? Supporting PMSA guests
as well?
Just asking to check whether the !XEN part would be in the right place
then.

>  	 * Check MSA_frac, bits [55:52]:
> @@ -107,6 +108,12 @@ reset_at_el2:
>  	mov	w0, #SPSR_KERNEL_EL1
>  	ldr	x1, =spsr_to_elx
>  	str	w0, [x1]
> +#else
> +	/* Start XEN on Armv8-R at EL2 */
> +	mov	w0, #1
> +	ldr	x1, =flag_keep_el
> +	str	w0, [x1]
> +#endif
>  
>  	cpuid	x0, x1
>  	bl	find_logical_id
> diff --git a/configure.ac b/configure.ac
> index 44459a4c849e..a5175db4148a 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -95,6 +95,9 @@ AM_CONDITIONAL([PSCI_HVC], [test "x$USE_PSCI" = "xhvc"])
>  AS_IF([test "x$USE_PSCI" = "xno" -a "x$KERNEL_ES" = "x32"],
>  	[AC_MSG_ERROR([With an AArch32 kernel, boot method must be PSCI.])]
>  )
> +AS_IF([test "x$USE_PSCI" = "xhvc" -a "x$X_IMAGE" != "x"],
> +	[AC_MSG_ERROR([With Xen kernel, PSCI conduit must be smc.])]
> +)

As mentioned above, I am not sure this is too helpful.

Cheers,
Andre

>  AC_SUBST([PSCI_METHOD], [$USE_PSCI])
>  
>  # Allow a user to pass --with-initrd