Re: [Xen-devel] Interaction between ACPI and dt_unreserved_regions() (WAS: Re: [PATCH] xen/arm: vgic-v3: Fix the typo of GICD IRQ active status range)

[Wei Xu <xuwei5@hisilicon.com>]

On 2020/1/18 4:41, Julien Grall wrote:
> (Renaming the title to avoid confusion)
>
> On 17/01/2020 09:06, Wei Xu wrote:
>> Hi Julien,
>
> Hi Wei,
>
>> On 2020/1/7 23:12, Julien Grall wrote:
>> Sorry for the late reply!
>
> Don't worry, thank you for looking into the bug!
>
>> The PC refers to fdt_num_mem_rsv during init_done.
>> But the device_tree_flattened is NULL that the data abort happened.
>
> Ah, I didn't realize that device_tree_flattened where still used 
> afterwards. Sorry for the breakage. I really need to setup a devbox 
> with ACPI so I can test changes properly.
>
>> So I added below changes and the XEN dom0 can be booted.
>>
>>      diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
>>      index 1e83351..1ab80a1 100644
>>      --- a/xen/arch/arm/setup.c
>>      +++ b/xen/arch/arm/setup.c
>>      @@ -392,7 +392,8 @@ void __init discard_initial_modules(void)
>>                    !mfn_valid(maddr_to_mfn(e)) )
>>                   continue;
>>
>>      -        dt_unreserved_regions(s, e, init_domheap_pages, 0);
>>      +       if( acpi_disabled )
>>      +           dt_unreserved_regions(s, e, init_domheap_pages, 0);
>
> While I understand how this is fixing your problem, this unfortunately 
> means the memory ranges used by the inital modules (e.g Kernel, 
> Initrd) will not be re-used by Xen. So this is a "slight" waste of 
> memory.
>
> There are a few other places where dt_unreserved_regions() is called 
> (see setup_mm()). However, in the case of setup_mm() we have a pointer 
> to DT as we don't know yet we are running on ACPI systems.
>
> But it feels wrong to try to find out the reserved memory range 
> through the DT when ACPI will be used. The DT is either going to be 
> nearly empty, or contain the full description of the platform. I don't 
> know enough to be able to say if something is going to go wrong.
>
> I am thinking to suggest to create an helper that will do the job for 
> you. Something like:
>
> void fwtable_unreserved_regions(paddr_t s, paddr_t e,
>                                 void (*cb)(paddr_t, paddr_t), int first)
> {
>    if ( acpi_disabled )
>      dt_unreserved_regions(s, e, cb, first);
>    else
>      cb(s, e);
> }
>
> Regarding the else part, this may need some adjustment if we need to 
> skip some reserved region for ACPI. On Xen 4.13, we should only have 
> usuable RAM in hand (the EFI stub is doing to sorting for us). Do you 
> know whether ACPI describes something similar to reserved-memory in DT 
> (i.e RAM regions reserved for cma...)?
>

Hi Julien,

I think UEFI describes it via ARM_MEMORY_REGION_DESCRIPTOR[1]
and XEN parses it at efi_init_memory but I did not find where to reserve 
the memory.

1: 
https://github.com/tianocore/edk2-platforms/blob/master/Platform/ARM/JunoPkg/Library/ArmJunoLib/ArmJunoMem.c

Thanks!

Best Regards,
Wei

> Cheers,
>



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