Re: [PATCH v6 2/3] arm64/mm: add set_direct_map_ro_noflush()

[Will Deacon <will@kernel.org>]

On Tue, Aug 25, 2026 at 05:52:20PM +0200, David Hildenbrand (Arm) wrote:
> On 7/30/26 11:06, Xueyuan Chen wrote:
> > Implement set_direct_map_ro_noflush() for arm64 with update_range_prot() on
> > the linear map, setting PTE_RDONLY and clearing PTE_WRITE. Keep the
> > existing can_set_direct_map() guard and leave TLB invalidation to the
> > caller.
> > 
> > Co-developed-by: Lance Yang <lance.yang@linux.dev>
> > Signed-off-by: Lance Yang <lance.yang@linux.dev>
> > Signed-off-by: Xueyuan Chen <xueyuan.chen21@gmail.com>
> > ---
> >  arch/arm64/include/asm/set_memory.h |  2 ++
> >  arch/arm64/mm/pageattr.c            | 10 ++++++++++
> >  2 files changed, 12 insertions(+)
> > 
> > diff --git a/arch/arm64/include/asm/set_memory.h b/arch/arm64/include/asm/set_memory.h
> > index 90f61b17275e..7083260303c3 100644
> > --- a/arch/arm64/include/asm/set_memory.h
> > +++ b/arch/arm64/include/asm/set_memory.h
> > @@ -14,6 +14,8 @@ int set_memory_valid(unsigned long addr, int numpages, int enable);
> >  int set_direct_map_invalid_noflush(struct page *page);
> >  int set_direct_map_default_noflush(struct page *page);
> >  int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid);
> > +int set_direct_map_ro_noflush(const void *addr, unsigned long nr_pages);
> > +#define set_direct_map_ro_noflush set_direct_map_ro_noflush
> >  bool kernel_page_present(struct page *page);
> >  
> >  int set_memory_encrypted(unsigned long addr, int numpages);
> > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> > index ce035e1b4eaf..c51236b61651 100644
> > --- a/arch/arm64/mm/pageattr.c
> > +++ b/arch/arm64/mm/pageattr.c
> > @@ -365,6 +365,16 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
> >  	return set_memory_valid(addr, nr, valid);
> >  }
> >  
> > +int set_direct_map_ro_noflush(const void *addr, unsigned long nr_pages)
> > +{
> > +	if (!can_set_direct_map())
> > +		return 0;
> > +
> > +	return update_range_prot((unsigned long)addr, PAGE_SIZE * nr_pages,
> > +				 __pgprot(PTE_RDONLY),
> > +				 __pgprot(PTE_WRITE));
> > +}
> > +
> >  #ifdef CONFIG_DEBUG_PAGEALLOC
> >  /*
> >   * This is - apart from the return value - doing the same
> 
> We'll need an ACK from arm64 maintaines. To me this looks good.

I generally dislike deferring critical things like TLB invalidation to
the caller, so it would be good to see an example of a caller that really
needs that. The caller in patch 1 unconditionally  calls
flush_tlb_kernel_range() immediately after calling
set_direct_map_ro_noflush().

In fact, that means we have a pointless invalidation if
!can_set_direct_map(). See exhibit A :)

Will