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

[Mike Rapoport <rppt@kernel.org>]

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.

Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>

> 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
> > > 
> 

-- 
Sincerely yours,
Mike.

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