Re: [PATCH v3 1/3] arm/efi: Introduce uefi,cfg-load DT property

[Luca Fancellu <luca.fancellu@xxxxxxx>]

> On Tue, 28 Sep 2021, Luca Fancellu wrote:
>> Introduce the uefi,cfg-load DT property of /chosen
>> node for ARM whose presence decide whether to force
>> the load of the UEFI Xen configuration file.
>> 
>> The logic is that if any multiboot,module is found in
>> the DT, then the uefi,cfg-load property is used to see
>> if the UEFI Xen configuration file is needed.
>> 
>> Modify a comment in efi_arch_use_config_file, removing
>> the part that states "dom0 required" because it's not
>> true anymore with this commit.
>> 
>> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> 
> The patch looks good. Only one minor change: given that this is a Xen
> parameter that we are introducing and not a parameter defined by UEFI
> Forum, I think uefi,cfg-load should be called xen,uefi-cfg-load instead.
> Because "xen," is our prefix, while "uefi," is not.
> 
> With that minor change:
> 
> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

Yes I will rename it.

> 
> 
> Note that the uefi,binary property is different because that property is
> for xen,domain nodes, so we are already in a Xen specific namespace when
> we are using it. Instead this property is for /chosen which is not a Xen
> specific node.

Given that uefi,binary will be used also for multiboot,module directly under 
/chosen
for Dom0, do you think I should rename also that to xen,uefi-binary?

Cheers,
Luca

> 
> 
> 
>> ---
>> v3 changes:
>> - add documentation to misc/arm/device-tree/booting.txt
>> - Modified variable name and logic from skip_cfg_file to
>> load_cfg_file
>> - Add in the commit message that I'm modifying a comment.
>> v2 changes:
>> - Introduced uefi,cfg-load property
>> - Add documentation about the property
>> ---
>> docs/misc/arm/device-tree/booting.txt |  8 ++++++++
>> docs/misc/efi.pandoc                  |  2 ++
>> xen/arch/arm/efi/efi-boot.h           | 28 ++++++++++++++++++++++-----
>> 3 files changed, 33 insertions(+), 5 deletions(-)
>> 
>> diff --git a/docs/misc/arm/device-tree/booting.txt 
>> b/docs/misc/arm/device-tree/booting.txt
>> index 44cd9e1a9a..cf878b478e 100644
>> --- a/docs/misc/arm/device-tree/booting.txt
>> +++ b/docs/misc/arm/device-tree/booting.txt
>> @@ -121,6 +121,14 @@ A Xen-aware bootloader would set xen,xen-bootargs for 
>> Xen, xen,dom0-bootargs
>> for Dom0 and bootargs for native Linux.
>> 
>> 
>> +UEFI boot and DT
>> +================
>> +
>> +When Xen is booted using UEFI, it doesn't read the configuration file if any
>> +multiboot module is specified. To force Xen to load the configuration file, 
>> the
>> +boolean property uefi,cfg-load must be declared in the /chosen node.
>> +
>> +
>> Creating Multiple Domains directly from Xen
>> ===========================================
>> 
>> diff --git a/docs/misc/efi.pandoc b/docs/misc/efi.pandoc
>> index ac3cd58cae..e289c5e7ba 100644
>> --- a/docs/misc/efi.pandoc
>> +++ b/docs/misc/efi.pandoc
>> @@ -14,6 +14,8 @@ loaded the modules and describes them in the device tree 
>> provided to Xen.  If a
>> bootloader provides a device tree containing modules then any configuration
>> files are ignored, and the bootloader is responsible for populating all
>> relevant device tree nodes.
>> +The property "uefi,cfg-load" can be specified in the /chosen node to force 
>> Xen
>> +to load the configuration file even if multiboot modules are found.
>> 
>> Once built, `make install-xen` will place the resulting binary directly into
>> the EFI boot partition, provided `EFI_VENDOR` is set in the environment (and
>> diff --git a/xen/arch/arm/efi/efi-boot.h b/xen/arch/arm/efi/efi-boot.h
>> index cf9c37153f..4f1b01757d 100644
>> --- a/xen/arch/arm/efi/efi-boot.h
>> +++ b/xen/arch/arm/efi/efi-boot.h
>> @@ -581,22 +581,40 @@ static void __init 
>> efi_arch_load_addr_check(EFI_LOADED_IMAGE *loaded_image)
>> 
>> static bool __init efi_arch_use_config_file(EFI_SYSTEM_TABLE *SystemTable)
>> {
>> +    bool load_cfg_file = true;
>>     /*
>>      * For arm, we may get a device tree from GRUB (or other bootloader)
>>      * that contains modules that have already been loaded into memory.  In
>> -     * this case, we do not use a configuration file, and rely on the
>> -     * bootloader to have loaded all required modules and appropriate
>> -     * options.
>> +     * this case, we search for the property uefi,cfg-load in the /chosen 
>> node
>> +     * to decide whether to skip the UEFI Xen configuration file or not.
>>      */
>> 
>>     fdt = lookup_fdt_config_table(SystemTable);
>>     dtbfile.ptr = fdt;
>>     dtbfile.need_to_free = false; /* Config table memory can't be freed. */
>> -    if ( !fdt || fdt_node_offset_by_compatible(fdt, 0, "multiboot,module") 
>> < 0 )
>> +
>> +    if ( fdt_node_offset_by_compatible(fdt, 0, "multiboot,module") > 0 )
>> +    {
>> +        /* Locate chosen node */
>> +        int node = fdt_subnode_offset(fdt, 0, "chosen");
>> +        const void *cfg_load_prop;
>> +        int cfg_load_len;
>> +
>> +        if ( node > 0 )
>> +        {
>> +            /* Check if uefi,cfg-load property exists */
>> +            cfg_load_prop = fdt_getprop(fdt, node, "uefi,cfg-load",
>> +                                        &cfg_load_len);
>> +            if ( !cfg_load_prop )
>> +                load_cfg_file = false;
>> +        }
>> +    }
>> +
>> +    if ( !fdt || load_cfg_file )
>>     {
>>         /*
>>          * We either have no FDT, or one without modules, so we must have a
>> -         * Xen EFI configuration file to specify modules.  (dom0 required)
>> +         * Xen EFI configuration file to specify modules.
>>          */
>>         return true;
>>     }
>> -- 
>> 2.17.1
>>