Re: [PATCH 03/11] xen/arm: Introduce a generic way to access memory bank structures

[Luca Fancellu <Luca.Fancellu@xxxxxxx>]

> On 19 Mar 2024, at 13:10, Michal Orzel <michal.orzel@xxxxxxx> wrote:
> 
> Hi Luca,

Hi Michal,

Thanks for having a look

> 
> On 12/03/2024 14:03, Luca Fancellu wrote:
>> 
>> 
>> Currently the 'stuct meminfo' is defining a static defined array of
>> 'struct membank' of NR_MEM_BANKS elements, some feature like
>> shared memory don't require such amount of memory allocation but
>> might want to reuse existing code to manipulate this kind of
>> structure that is just as 'struct meminfo' but less bulky.
>> 
>> For this reason introduce a generic way to access this kind of
>> structure using a new stucture 'struct membanks', which implements
> s/stucture/structure
> 
>> all the fields needed by a structure related to memory banks
>> without the need to specify at build time the size of the
>> 'struct membank' array.
> Might be beneficial here to mention the use of FAM.
> 
>> 
>> Modify 'struct meminfo' to implement the field related to the new
>> introduced structure, given the change all usage of this structure
>> are updated in this way:
>> - code accessing bootinfo.{mem,reserved_mem,acpi} field now uses
>>   3 new introduced static inline helpers to access the new field
>>   of 'struct meminfo' named 'common'.
>> - code accessing 'struct kernel_info *' member 'mem' now use the
>>   new introduced macro 'kernel_info_get_mem(...)' to access the
>>   new field of 'struct meminfo' named 'common'.
>> 
>> Constify pointers where needed.
>> 
>> Suggested-by: Julien Grall <julien@xxxxxxx>
>> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
>> ---
>> xen/arch/arm/acpi/domain_build.c        |   6 +-
>> xen/arch/arm/arm32/mmu/mm.c             |  44 +++++-----
>> xen/arch/arm/arm64/mmu/mm.c             |   2 +-
>> xen/arch/arm/bootfdt.c                  |  27 +++---
>> xen/arch/arm/dom0less-build.c           |  18 ++--
>> xen/arch/arm/domain_build.c             | 106 +++++++++++++-----------
>> xen/arch/arm/efi/efi-boot.h             |   8 +-
>> xen/arch/arm/efi/efi-dom0.c             |  13 +--
>> xen/arch/arm/include/asm/domain_build.h |   2 +-
>> xen/arch/arm/include/asm/kernel.h       |   9 ++
>> xen/arch/arm/include/asm/setup.h        |  40 ++++++++-
>> xen/arch/arm/include/asm/static-shmem.h |   4 +-
>> xen/arch/arm/kernel.c                   |  12 +--
>> xen/arch/arm/setup.c                    |  58 +++++++------
>> xen/arch/arm/static-memory.c            |  27 +++---
>> xen/arch/arm/static-shmem.c             |  34 ++++----
>> 16 files changed, 243 insertions(+), 167 deletions(-)
> Lots of mechanical changes but in general I like this approach.
> I'd like other maintainers to share their opinion.
> 
> [...]
> 
>> @@ -1157,10 +1163,12 @@ int __init make_hypervisor_node(struct domain *d,
>>     }
>>     else
>>     {
>> -        ext_regions = xzalloc(struct meminfo);
>> +        ext_regions = (struct membanks *)xzalloc(struct meminfo);
> You're making assumption that struct membanks is the first member of meminfo 
> but there's no sanity check.
> Why not xzalloc_flex_struct()?

I’ll use that, as well as the check you suggested below

> 
>>         if ( !ext_regions )
>>             return -ENOMEM;
> 
> [...]
>> diff --git a/xen/arch/arm/include/asm/kernel.h 
>> b/xen/arch/arm/include/asm/kernel.h
>> index 0a23e86c2d37..d28b843c01a9 100644
>> --- a/xen/arch/arm/include/asm/kernel.h
>> +++ b/xen/arch/arm/include/asm/kernel.h
>> @@ -78,6 +78,15 @@ struct kernel_info {
>>     };
>> };
>> 
>> +#define kernel_info_get_mem(kinfo) \
>> +    (&(kinfo)->mem.common)
> Why this is a macro but for bootinfo you use static inline helpers?

So I think I started using static inline helpers but I had to have one that 
didn’t
remove the const qualifier, and it was used only once. Anyway if it is 
acceptable
I will go for static inline also here.

> 
>> +
>> +#define KERNEL_INFO_INIT \
> NIT: in most places we prefer \ to be aligned (the same apply to other places)

kk

> 
>> +{ \
>> +    .mem.common.max_banks = NR_MEM_BANKS, \
>> +    .shm_mem.common.max_banks = NR_MEM_BANKS, \
>> +}
>> +
>> /*
>>  * Probe the kernel to detemine its type and select a loader.
>>  *
>> diff --git a/xen/arch/arm/include/asm/setup.h 
>> b/xen/arch/arm/include/asm/setup.h
>> index d15a88d2e0d1..a3e1dc8fdb6c 100644
>> --- a/xen/arch/arm/include/asm/setup.h
>> +++ b/xen/arch/arm/include/asm/setup.h
>> @@ -56,8 +56,14 @@ struct membank {
>> #endif
>> };
>> 
>> -struct meminfo {
>> +struct membanks {
>>     unsigned int nr_banks;
>> +    unsigned int max_banks;
>> +    struct membank bank[];
>> +};
>> +
>> +struct meminfo {
>> +    struct membanks common;
> You were supposed to make sure there is no extra padding here. I don't see 
> any check in this patch.
> I'd at least do sth like:
> BUILD_BUG_ON((offsetof(struct membanks, bank)) != (offsetof(struct meminfo, 
> bank)));

I’ll add this check, thanks!

> 
> ~Michal