Re: [PATCH v8 2/4] mm: Introduce memblock_isolate_memory

[Alexandre Ghiti <alex@ghiti.fr>]

On 3/23/23 13:16, Mike Rapoport wrote:
> On Thu, Mar 23, 2023 at 12:52:36PM +0100, Alexandre Ghiti wrote:
>> On 3/20/23 18:44, Mike Rapoport wrote:
>>> On Mon, Mar 20, 2023 at 11:54:14AM +0100, Alexandre Ghiti wrote:
>>>> Hi Mike,
>>>>
>>>> On 3/16/23 21:12, Mike Rapoport wrote:
>>>>> Hi Alexandre,
>>>>>
>>>>> On Thu, Mar 16, 2023 at 02:17:09PM +0100, Alexandre Ghiti wrote:
>>>>>> This function allows to split a region in memblock.memory and will be
>>>>>> useful when setting up the linear mapping with STRICT_KERNEL_RWX: it
>>>>>> allows to isolate the kernel text/rodata and then avoid to map those
>>>>>> regions with a PUD/P4D/PGD.
>>>>> Sorry I've missed it last time. The changelog is fine in the context of
>>>> No worries :)
>>>>
>>>>
>>>>> this series, but if you look at it as a part of memblock changelog it
>>>>> doesn't provide enough background on why memblock_isolate_memory() is
>>>>> useful.
>>>>>
>>>>> Can you please add more context so it would be self explanatory?
>>>> What about: "memblock.memory contains the list of memory regions and a
>>>> memory region can cover memory that will be mapped with different
>>>> permissions. So to ease the mapping process, allow to isolate those regions
>>>> by introducing a new function called memblock_isolate_memory. This will be
>>>> used in arch specific code to isolate the kernel text/rodata regions when
>>>> STRICT_KERNEL_RWX is enabled so that we avoid mapping them with PUD/P4D/PGD
>>>> mappings."
>>> With this change
>>>
>>> ... STRICT_KERNEL_RWX is enabled so that they can be mapped with base pages.
>>
>> Actually they will get mapped with PMD mappings :) I'll just append: "or PMD
>> mapping" to your sentence above if that's ok with you.
> Didn't read the rest of the patches :)
>
> .. STRICT_KERNEL_RWX is enabled so that they can be mapped with differently
> than the rest of the memory.
>
> Does it cover the usescases?


Yes, fine with me!

Thanks again


>
>>> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
>>
>> Thanks for your review,
>>
>> Alex
>>
>>
>>>> Thanks,
>>>>
>>>> Alex
>>>>
>>>>
>>>>>> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
>>>>>> Reviewed-by: Anup Patel <anup@brainfault.org>
>>>>>> Tested-by: Anup Patel <anup@brainfault.org>
>>>>>> ---
>>>>>>     include/linux/memblock.h |  1 +
>>>>>>     mm/memblock.c            | 20 ++++++++++++++++++++
>>>>>>     2 files changed, 21 insertions(+)
>>>>>>
>>>>>> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>>>>>> index 50ad19662a32..2f7ef97c0da7 100644
>>>>>> --- a/include/linux/memblock.h
>>>>>> +++ b/include/linux/memblock.h
>>>>>> @@ -125,6 +125,7 @@ int memblock_clear_hotplug(phys_addr_t base, phys_addr_t size);
>>>>>>     int memblock_mark_mirror(phys_addr_t base, phys_addr_t size);
>>>>>>     int memblock_mark_nomap(phys_addr_t base, phys_addr_t size);
>>>>>>     int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
>>>>>> +int memblock_isolate_memory(phys_addr_t base, phys_addr_t size);
>>>>>>     void memblock_free_all(void);
>>>>>>     void memblock_free(void *ptr, size_t size);
>>>>>> diff --git a/mm/memblock.c b/mm/memblock.c
>>>>>> index 25fd0626a9e7..e8c651a37012 100644
>>>>>> --- a/mm/memblock.c
>>>>>> +++ b/mm/memblock.c
>>>>>> @@ -805,6 +805,26 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
>>>>>>     	return 0;
>>>>>>     }
>>>>>> +/**
>>>>>> + * memblock_isolate_memory - isolate given range in memblock.memory
>>>>>> + * @base: base of range to isolate
>>>>>> + * @size: size of range to isolate
>>>>>> + *
>>>>>> + * Isolates the given range in memblock.memory so that it does not share any
>>>>>> + * region with other ranges.
>>>>>> + *
>>>>>> + * Return:
>>>>>> + * 0 on success, -errno on failure.
>>>>>> + */
>>>>>> +
>>>>>> +int __init_memblock memblock_isolate_memory(phys_addr_t base, phys_addr_t size)
>>>>>> +{
>>>>>> +	int start_rgn, end_rgn;
>>>>>> +
>>>>>> +	return memblock_isolate_range(&memblock.memory, base, size,
>>>>>> +				      &start_rgn, &end_rgn);
>>>>>> +}
>>>>>> +
>>>>>>     static int __init_memblock memblock_remove_range(struct memblock_type *type,
>>>>>>     					  phys_addr_t base, phys_addr_t size)
>>>>>>     {
>>>>>> -- 
>>>>>> 2.37.2
>>>>>>