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

Alexandre Ghiti
2023-03-23T11:53:43Z

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.

>
> 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
>>>>