Re: [PATCH] efi/libstub/fdt: Standardize the names of EFI stub parameters

[Shannon Zhao]

On 2015/9/11 23:45, Daniel Kiper wrote:
> On Fri, Sep 11, 2015 at 03:30:15PM +0200, Ard Biesheuvel wrote:
>> On 11 September 2015 at 15:14, Stefano Stabellini
>> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>>> On Fri, 11 Sep 2015, Daniel Kiper wrote:
>>>> On Thu, Sep 10, 2015 at 05:23:02PM +0100, Mark Rutland wrote:
>>>>>>> C) When you could go:
>>>>>>>
>>>>>>>    DT -> Discover Xen -> Xen-specific stuff -> Xen-specific EFI/ACPI discovery
>>>>>>
>>>>>> I take you mean discovering Xen with the usual Xen hypervisor node on
>>>>>> device tree. I think that C) is a good option actually. I like it. Not
>>>>>> sure why we didn't think about this earlier. Is there anything EFI or
>>>>>> ACPI which is needed before Xen support is discovered by
>>>>>> arch/arm64/kernel/setup.c:setup_arch -> xen_early_init()?
>>>>>
>>>>> Currently lots (including the memory map). With the stuff to support
>>>>> SPCR, the ACPI discovery would be moved before xen_early_init().
>>>>>
>>>>>> If not, we could just go for this. A lot of complexity would go away.
>>>>>
>>>>> I suspect this would still be fairly complex, but would at least prevent
>>>>> the Xen-specific EFI handling from adversely affecting the native case.
>>>>>
>>>>>>> D) If you want to be generic:
>>>>>>>    EFI -> EFI application -> EFI tables -> ACPI tables -> Xen-specific stuff
>>>>>>>           \------------------------------------------/
>>>>>>>            (virtualize these, provide shims to Dom0, but handle
>>>>>>>             everything in Xen itself)
>>>>>>
>>>>>> I think that this is good in theory but could turn out to be a lot of
>>>>>> work in practice. We could probably virtualize the RuntimeServices but
>>>>>> the BootServices are troublesome.
>>>>>
>>>>> What's troublesome with the boot services?
>>>>>
>>>>> What can't be simulated?
>>>>
>>>> How do you want to access bare metal EFI boot services from dom0 if they
>>>> were shutdown long time ago before loading dom0 image? What do you need
>>>> from EFI boot services in dom0?
>>>
>>> That's right. Trying to emulate BootServices after the real
>>> ExitBootServices has already been called seems like a very bad plan.
>>>
>>> I think that whatever interface we come up with, would need to be past
>>> ExitBootServices.
>>
>> It feels like this discussion is going in circles.
>>
>> When we discussed this six months ago, we already concluded that,
>> since UEFI is the only specified way that the presence of ACPI is
>> advertised on an ARM system, we need to emulate UEFI to some extent.
>>
>> So we need the EFI system table to expose the UEFI configuration table
>> that carries the ACPI root pointer.
>>
>> Since ACPI support also relies on the UEFI memory map (I think?), we
>> need that as well.
>>
>> These two items are exactly what we pass via the UEFI DT properties,
>> so we should indeed promote the current de-facto binding to a proper
>> binding, and renaming the properties makes sense in that context.
>>
>> I agree that this should also include a description of the expected
>> state of the firmware, i.e., that ExitBootServices() has been called,
>> and that the memory map has been populated with virtual address, which
>> have been installed using SetVirtualAddressMap() if they differ from
>> the physical addresses. (The current implementation on the kernel side
>> is perfectly capable of dealing with a 1:1 mapping).
>>
>> Beyond that, there is no point in pretending to be a full UEFI
>> implementation, imo. Boot services are not required, nor are runtime
>> services (only the current EFI init code on arm needs to be modified
>> to deal with a NULL runtime services pointer)
> 
> Taking into account above I think that you have most of the code in place.
> Please take a look at linux/arch/x86/xen/efi.c, linux/drivers/acpi/osl.c
> and linux/drivers/xen/efi.c (maybe somewhere else). In general you should
> create ARM version of xen_efi_init() (x86 version you can find in
> linux/drivers/xen/efi.c; it is very simple thing), maybe add some
> code in a few places and voila.
> 

It only needs to apply following patch to fix a bug in Linux kernel when
mapping EFI_MEMORY_RUNTIME memory.

Author: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
Date:   Thu Aug 20 14:54:58 2015 +0800

    arm64/efi: Fix a bug when no EFI_MEMORY_RUNTIME memory found

    Currently if the attribute type of all the EFI Memory Descriptors are
    not EFI_MEMORY_RUNTIME, efi_virtmap_init will return true. But at this
    case, it expect false as there are no EFI memory for RUNTIME. Fix it by
    introducing a status to show whether it finds EFI_MEMORY_RUNTIME.

    Signed-off-by: Shannon Zhao <shannon.zhao@xxxxxxxxxx>

diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index e8ca6ea..bad7f87 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -233,6 +233,7 @@ void __init efi_init(void)
 static bool __init efi_virtmap_init(void)
 {
        efi_memory_desc_t *md;
+       bool status = false;

        for_each_efi_memory_desc(&memmap, md) {
                u64 paddr, npages, size;
@@ -264,8 +265,11 @@ static bool __init efi_virtmap_init(void)
                        prot = PAGE_KERNEL;

                create_pgd_mapping(&efi_mm, paddr, md->virt_addr, size,
prot);
+               status = true;
        }
-       return true;
+       if (status)
+               return true;
+       return false;
 }

-- 
Shannon

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