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

[Alexandre Ghiti]

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@xxxxxxxxxxxx>
> > Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>
> > Tested-by: Anup Patel <anup@xxxxxxxxxxxxxx>
> > ---
> >   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