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

[Luca Fancellu]

Hi Andre,

> On 21 Jun 2024, at 11:36, Andre Przywara <Andre.Przywara at arm.com> wrote:
> 
> 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.

Yes, it’s only the current Xen implementation that doesn’t 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.

Xen does not care and it just leaves the EL1 setup to the guest.

> 
>> * 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.

Ok, so your proposal is to remove this check, am I right?

Cheers,
Luca