Re: [PATCH V4 2/7] powerpc/mm: Enable ARCH_HAS_VM_GET_PAGE_PROT

[Christophe Leroy]

Le 08/04/2022 à 14:53, Christophe Leroy a écrit :
> Le 07/04/2022 à 12:32, Anshuman Khandual a écrit :
> > This defines and exports a platform specific custom vm_get_page_prot() 
> > via
> > subscribing ARCH_HAS_VM_GET_PAGE_PROT. While here, this also localizes
> > arch_vm_get_page_prot() as powerpc_vm_get_page_prot() and moves it near
> > vm_get_page_prot().
> >
> > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > Cc: Paul Mackerras <paulus@xxxxxxxxx>
> > Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> > ---
> >   arch/powerpc/Kconfig            |  1 +
> >   arch/powerpc/include/asm/mman.h | 12 ------------
> >   arch/powerpc/mm/mmap.c          | 26 ++++++++++++++++++++++++++
> >   3 files changed, 27 insertions(+), 12 deletions(-)
> >
> > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > index 174edabb74fa..eb9b6ddbf92f 100644
> > --- a/arch/powerpc/Kconfig
> > +++ b/arch/powerpc/Kconfig
> > @@ -140,6 +140,7 @@ config PPC
> >       select ARCH_HAS_TICK_BROADCAST        if 
> > GENERIC_CLOCKEVENTS_BROADCAST
> >       select ARCH_HAS_UACCESS_FLUSHCACHE
> >       select ARCH_HAS_UBSAN_SANITIZE_ALL
> > +    select ARCH_HAS_VM_GET_PAGE_PROT
> >       select ARCH_HAVE_NMI_SAFE_CMPXCHG
> >       select ARCH_KEEP_MEMBLOCK
> >       select ARCH_MIGHT_HAVE_PC_PARPORT
> > diff --git a/arch/powerpc/include/asm/mman.h 
> > b/arch/powerpc/include/asm/mman.h
> > index 7cb6d18f5cd6..1b024e64c8ec 100644
> > --- a/arch/powerpc/include/asm/mman.h
> > +++ b/arch/powerpc/include/asm/mman.h
> > @@ -24,18 +24,6 @@ static inline unsigned long 
> > arch_calc_vm_prot_bits(unsigned long prot,
> >   }
> >   #define arch_calc_vm_prot_bits(prot, pkey) 
> > arch_calc_vm_prot_bits(prot, pkey)
> > -static inline pgprot_t arch_vm_get_page_prot(unsigned long vm_flags)
> > -{
> > -#ifdef CONFIG_PPC_MEM_KEYS
> > -    return (vm_flags & VM_SAO) ?
> > -        __pgprot(_PAGE_SAO | vmflag_to_pte_pkey_bits(vm_flags)) :
> > -        __pgprot(0 | vmflag_to_pte_pkey_bits(vm_flags));
> > -#else
> > -    return (vm_flags & VM_SAO) ? __pgprot(_PAGE_SAO) : __pgprot(0);
> > -#endif
> > -}
> > -#define arch_vm_get_page_prot(vm_flags) arch_vm_get_page_prot(vm_flags)
> > -
> >   static inline bool arch_validate_prot(unsigned long prot, unsigned 
> > long addr)
> >   {
> >       if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM | 
> > PROT_SAO))
> > diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
> > index c475cf810aa8..cd17bd6fa36b 100644
> > --- a/arch/powerpc/mm/mmap.c
> > +++ b/arch/powerpc/mm/mmap.c
> > @@ -254,3 +254,29 @@ void arch_pick_mmap_layout(struct mm_struct *mm, 
> > struct rlimit *rlim_stack)
> >           mm->get_unmapped_area = arch_get_unmapped_area_topdown;
> >       }
> >   }
> > +
> > +#ifdef CONFIG_PPC64
> > +static pgprot_t powerpc_vm_get_page_prot(unsigned long vm_flags)
> > +{
> > +#ifdef CONFIG_PPC_MEM_KEYS
> > +    return (vm_flags & VM_SAO) ?
> > +        __pgprot(_PAGE_SAO | vmflag_to_pte_pkey_bits(vm_flags)) :
> > +        __pgprot(0 | vmflag_to_pte_pkey_bits(vm_flags));
> > +#else
> > +    return (vm_flags & VM_SAO) ? __pgprot(_PAGE_SAO) : __pgprot(0);
> > +#endif
> > +}
> > +#else
> > +static pgprot_t powerpc_vm_get_page_prot(unsigned long vm_flags)
> > +{
> > +    return __pgprot(0);
> > +}
> > +#endif /* CONFIG_PPC64 */
>
> Can we reduce this forest of #ifdefs and make it more readable ?
>
> mm/mmap.c is going away with patch 
> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/d6d849621f821af253e777a24eda4c648814a76e.1646847562.git.christophe.leroy@xxxxxxxxxx/ 
>
>
> So it would be better to add two versions of vm_get_page_prot(), for 
> instance one in mm/pgtable_64.c and one in mm/pgtable_32.c

Indeed, you don't need anything at all for PPC32. All you need to do is

	select ARCH_HAS_VM_GET_PAGE_PROT if PPC64

And in fact it could even be PPC_BOOK3S_64 instead of PPC64 because 
CONFIG_PPC_MEM_KEYS depends on PPC_BOOK3S_64 and _PAGE_SAO is 0 on 
nohash/64.

So you can then put it into arch/powerpc/mm/book3s64/pgtable.c


> > +
> > +pgprot_t vm_get_page_prot(unsigned long vm_flags)
> > +{
> > +    return __pgprot(pgprot_val(protection_map[vm_flags &
> > +            (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
> > +           pgprot_val(powerpc_vm_get_page_prot(vm_flags)));
> > +}
> > +EXPORT_SYMBOL(vm_get_page_prot);
>
> By the way I'm a bit puzzled with the name powerpc_vm_get_page_prot(), 
> the name suggests that it's just a powerpc replacement of 
> vm_get_page_prot(). I'd prefer if it was named __vm_get_page_prot(), it 
> would be clearer that it is a complement to vm_get_page_prot() and not a 
> remplacement.
>
> Christophe