Re: [PATCH 06/15] x86/hyperlaunch: introduce the domain builder

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.12.2024 13:36, Daniel P. Smith wrote:
> On 12/2/24 05:10, Jan Beulich wrote:
>> On 23.11.2024 19:20, Daniel P. Smith wrote:
>>> Introduce the domain builder which is capable of consuming a device tree as 
>>> the
>>> first boot module. If it finds a device tree as the first boot module, it 
>>> will
>>> set its type to BOOTMOD_FDT. This change only detects the boot module and
>>> continues to boot with slight change to the boot convention that the dom0
>>> kernel is no longer first boot module but is the second.
>>>
>>> No functional change intended.
>>>
>>> Signed-off-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
>>> ---
>>>   xen/arch/x86/Makefile                    |  2 +
>>>   xen/arch/x86/domain_builder/Makefile     |  3 ++
>>>   xen/arch/x86/domain_builder/core.c       | 55 ++++++++++++++++++++++++
>>>   xen/arch/x86/domain_builder/fdt.c        | 38 ++++++++++++++++
>>>   xen/arch/x86/domain_builder/fdt.h        | 21 +++++++++
>>>   xen/arch/x86/include/asm/bootinfo.h      |  3 ++
>>>   xen/arch/x86/include/asm/domainbuilder.h |  8 ++++
>>>   xen/arch/x86/setup.c                     | 18 +++++---
>>>   8 files changed, 142 insertions(+), 6 deletions(-)
>>>   create mode 100644 xen/arch/x86/domain_builder/Makefile
>>>   create mode 100644 xen/arch/x86/domain_builder/core.c
>>>   create mode 100644 xen/arch/x86/domain_builder/fdt.c
>>>   create mode 100644 xen/arch/x86/domain_builder/fdt.h
>>
>> As I'm sure I indicated before: Dashes instead of underscores please in new
>> files' names.
>>
>>>   create mode 100644 xen/arch/x86/include/asm/domainbuilder.h
>>
>> Why is there no separator in this file's name?
> 
> Name was getting a bit long, but can add separator if desired.

Well, my desire is for the subdir and the header names to match up.
Personally I think that neater to achieve when both have a dash in the
middle.

>>> --- /dev/null
>>> +++ b/xen/arch/x86/domain_builder/core.c
>>> @@ -0,0 +1,55 @@
>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>> +/*
>>> + * Copyright (C) 2024, Apertus Solutions, LLC
>>> + */
>>> +#include <xen/err.h>
>>> +#include <xen/init.h>
>>> +#include <xen/kconfig.h>
>>> +#include <xen/lib.h>
>>> +
>>> +#include <asm/bootinfo.h>
>>> +
>>> +#include "fdt.h"
>>> +
>>> +void __init builder_init(struct boot_info *bi)
>>> +{
>>> +    if ( IS_ENABLED(CONFIG_DOMAIN_BUILDER) )
>>> +    {
>>> +        int ret;
>>> +
>>> +        switch ( ret = has_hyperlaunch_fdt(bi) )
>>> +        {
>>> +        case 0:
>>> +            printk("Hyperlaunch device tree detected\n");
>>> +            bi->hyperlaunch_enabled = true;
>>> +            bi->mods[0].type = BOOTMOD_FDT;
>>> +            break;
>>> +        case -EINVAL:
>>> +            printk("Hyperlaunch device tree was not detected\n");
>>> +            bi->hyperlaunch_enabled = false;
>>> +            break;
>>> +        case -ENOENT:
>>> +            fallthrough;
>>
>> No need for this.
> 
> I thought MISRA called for explicit fallthrough?

Only when there are statements between two case labels. Which ...

>>> +        case -ENODATA:

... isn't the case here.

>>> @@ -1277,9 +1278,12 @@ void asmlinkage __init noreturn __start_xen(void)
>>>                  bi->nr_modules);
>>>       }
>>>   
>>> -    /* Dom0 kernel is always first */
>>> -    bi->mods[0].type = BOOTMOD_KERNEL;
>>> -    bi->domains[0].kernel = &bi->mods[0];
>>> +    builder_init(bi);
>>> +
>>> +    /* Find first unknown boot module to use as Dom0 kernel */
>>> +    i = first_boot_module_index(bi, BOOTMOD_UNKNOWN);
>>> +    bi->mods[i].type = BOOTMOD_KERNEL;
>>> +    bi->domains[0].kernel = &bi->mods[i];
>>
>> Better latch the result here into a separate local variable, for use ...
>>
>>> @@ -1466,8 +1470,9 @@ void asmlinkage __init noreturn __start_xen(void)
>>>           xen->size  = __2M_rwdata_end - _stext;
>>>       }
>>>   
>>> -    bi->mods[0].headroom =
>>> -        bzimage_headroom(bootstrap_map_bm(&bi->mods[0]), bi->mods[0].size);
>>> +    i = first_boot_module_index(bi, BOOTMOD_KERNEL);
>>> +    bi->mods[i].headroom =
>>> +        bzimage_headroom(bootstrap_map_bm(&bi->mods[i]), bi->mods[i].size);
>>>       bootstrap_unmap();
>>>   
>>>   #ifndef highmem_start
>>> @@ -1591,7 +1596,8 @@ void asmlinkage __init noreturn __start_xen(void)
>>>   #endif
>>>       }
>>>   
>>> -    if ( bi->mods[0].headroom && !bi->mods[0].relocated )
>>> +    i = first_boot_module_index(bi, BOOTMOD_KERNEL);
>>> +    if ( bi->mods[i].headroom && !bi->mods[0].relocated )
>>>           panic("Not enough memory to relocate the dom0 kernel image\n");
>>>       for ( i = 0; i < bi->nr_modules; ++i )
>>>       {
>>
>> ... in these two places?
> 
> I don't know if a local variable is need. I assume your suggestion is to 
> drop the first_boot_module_index() call,

The latter two of the three, yes.

> but thinking about it, not sure 
> why I kept the walk. A direct use of bi->domains[0].kernel could be used 
> without the intermediate variable while removing the call.

If that's possible, the even better.

Jan