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

Alexandre Ghiti
2023-03-20T10:54:39Z

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."

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
>>