Re: [PATCH v4 3/3] xen/ppc: Implement initial Radix MMU support

[Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>]

On 9/5/23 5:01 AM, Jan Beulich wrote:
> On 23.08.2023 01:03, Shawn Anastasio wrote:
>> Add code to construct early identity-mapped page tables as well as the
>> required process and partition tables to enable the MMU.
>>
>> Signed-off-by: Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>
> 
> Having committed this, something broke in CI. As per the artifacts of
> https://gitlab.com/xen-project/xen/-/jobs/5017915681 ...
> 
>> +void __init setup_initial_pagetables(void)
>> +{
>> +    struct lvl1_pd *root = lvl1_pd_pool_alloc();
>> +    unsigned long lpcr;
>> +
>> +    setup_initial_mapping(root, (vaddr_t)_start, (vaddr_t)_end, 
>> __pa(_start));
>> +
>> +    /* Enable Radix mode in LPCR */
>> +    lpcr = mfspr(SPRN_LPCR);
>> +    mtspr(SPRN_LPCR, lpcr | LPCR_UPRT | LPCR_HR);
>> +    early_printk("Enabled radix in LPCR\n");
> 
> ... this is the first message missing; setup_initial_mapping() appears
> to be completing fine.

Ah, yes, this is a side-effect of the CI pipeline using the pseries
machine type instead of PowerNV. Setting the LPCR directly as we're
doing here has to be done via a hypercall on the paravirtualized pseries
platform.

I've given it some thought and I think the best path forward would be to
just drop pseries support. I had originally targeted it for the early
bringup patches since it has historically been much better supported by
QEMU, but that's no longer the case with QEMU git. Outside of testing I
don't think there's much practical value in continuing to support
pseries.

I'll prepare a series to drop pseries support and update the CI
container to use the PowerNV machine type instead, if there are no
objections.

> Jan

Thanks,
Shawn