Subject: Re: [RFC V1 04/31] powerpc/mm: Enable ARCH_HAS_VM_GET_PAGE_PROT

From: Mike Rapoport <[email-masked]>
Date: Fri, 4 Feb 2022 06:44:38 +0200

On Fri, Feb 04, 2022 at 08:27:37AM +0530, Anshuman Khandual wrote:
> 
> On 2/3/22 11:45 PM, Mike Rapoport wrote:
> > On Mon, Jan 24, 2022 at 06:26:41PM +0530, Anshuman Khandual wrote:
> >> This defines and exports a platform specific custom vm_get_page_prot() via
> >> subscribing ARCH_HAS_VM_GET_PAGE_PROT. Subsequently all __SXXX and __PXXX
> >> macros can be dropped which are no longer needed. While here, this also
> >> localizes arch_vm_get_page_prot() as powerpc_vm_get_page_prot().
> >>
> >> Cc: Michael Ellerman <[email-masked]>
> >> Cc: Paul Mackerras <[email-masked]>
> >> Cc: [email-masked]
> >> Cc: [email-masked]
> >> Signed-off-by: Anshuman Khandual <[email-masked]>
> >> ---
> >>  arch/powerpc/Kconfig               |  1 +
> >>  arch/powerpc/include/asm/mman.h    |  3 +-
> >>  arch/powerpc/include/asm/pgtable.h | 19 ------------
> >>  arch/powerpc/mm/mmap.c             | 47 ++++++++++++++++++++++++++++++
> >>  4 files changed, 49 insertions(+), 21 deletions(-)
> >>
> >> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> >> index b779603978e1..ddb4a3687c05 100644
> >> --- a/arch/powerpc/Kconfig
> >> +++ b/arch/powerpc/Kconfig
> >> @@ -135,6 +135,7 @@ 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..7b10c2031e82 100644
> >> --- a/arch/powerpc/include/asm/mman.h
> >> +++ b/arch/powerpc/include/asm/mman.h
> >> @@ -24,7 +24,7 @@ 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)
> >> +static inline pgprot_t powerpc_vm_get_page_prot(unsigned long vm_flags)
> >>  {
> >>  #ifdef CONFIG_PPC_MEM_KEYS
> >>  	return (vm_flags & VM_SAO) ?
> >> @@ -34,7 +34,6 @@ static inline pgprot_t arch_vm_get_page_prot(unsigned long vm_flags)
> >>  	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)
> >>  {
> >> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> >> index d564d0ecd4cd..3cbb6de20f9d 100644
> >> --- a/arch/powerpc/include/asm/pgtable.h
> >> +++ b/arch/powerpc/include/asm/pgtable.h
> >> @@ -20,25 +20,6 @@ struct mm_struct;
> >>  #include <asm/nohash/pgtable.h>
> >>  #endif /* !CONFIG_PPC_BOOK3S */
> >>  
> >> -/* Note due to the way vm flags are laid out, the bits are XWR */
> >> -#define __P000	PAGE_NONE
> >> -#define __P001	PAGE_READONLY
> >> -#define __P010	PAGE_COPY
> >> -#define __P011	PAGE_COPY
> >> -#define __P100	PAGE_READONLY_X
> >> -#define __P101	PAGE_READONLY_X
> >> -#define __P110	PAGE_COPY_X
> >> -#define __P111	PAGE_COPY_X
> >> -
> >> -#define __S000	PAGE_NONE
> >> -#define __S001	PAGE_READONLY
> >> -#define __S010	PAGE_SHARED
> >> -#define __S011	PAGE_SHARED
> >> -#define __S100	PAGE_READONLY_X
> >> -#define __S101	PAGE_READONLY_X
> >> -#define __S110	PAGE_SHARED_X
> >> -#define __S111	PAGE_SHARED_X
> >> -
> >>  #ifndef __ASSEMBLY__
> >>  
> >>  #ifndef MAX_PTRS_PER_PGD
> >> diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
> >> index c475cf810aa8..7f05e7903bd2 100644
> >> --- a/arch/powerpc/mm/mmap.c
> >> +++ b/arch/powerpc/mm/mmap.c
> >> @@ -254,3 +254,50 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
> >>  		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
> >>  	}
> >>  }
> >> +
> >> +static inline pgprot_t __vm_get_page_prot(unsigned long vm_flags)
> >> +{
> >> +	switch (vm_flags & (VM_READ | VM_WRITE | VM_EXEC | VM_SHARED)) {
> >> +	case VM_NONE:
> >> +		return PAGE_NONE;
> >> +	case VM_READ:
> >> +		return PAGE_READONLY;
> >> +	case VM_WRITE:
> >> +		return PAGE_COPY;
> >> +	case VM_READ | VM_WRITE:
> >> +		return PAGE_COPY;
> >> +	case VM_EXEC:
> >> +		return PAGE_READONLY_X;
> >> +	case VM_EXEC | VM_READ:
> >> +		return PAGE_READONLY_X;
> >> +	case VM_EXEC | VM_WRITE:
> >> +		return PAGE_COPY_X;
> >> +	case VM_EXEC | VM_READ | VM_WRITE:
> >> +		return PAGE_COPY_X;
> >> +	case VM_SHARED:
> >> +		return PAGE_NONE;
> >> +	case VM_SHARED | VM_READ:
> >> +		return PAGE_READONLY;
> >> +	case VM_SHARED | VM_WRITE:
> >> +		return PAGE_SHARED;
> >> +	case VM_SHARED | VM_READ | VM_WRITE:
> >> +		return PAGE_SHARED;
> >> +	case VM_SHARED | VM_EXEC:
> >> +		return PAGE_READONLY_X;
> >> +	case VM_SHARED | VM_EXEC | VM_READ:
> >> +		return PAGE_READONLY_X;
> >> +	case VM_SHARED | VM_EXEC | VM_WRITE:
> >> +		return PAGE_SHARED_X;
> >> +	case VM_SHARED | VM_EXEC | VM_READ | VM_WRITE:
> >> +		return PAGE_SHARED_X;
> >> +	default:
> >> +		BUILD_BUG();
> >> +	}
> >> +}
> >> +
> >> +pgprot_t vm_get_page_prot(unsigned long vm_flags)
> >> +{
> >> +	return __pgprot(pgprot_val(__vm_get_page_prot(vm_flags)) |
> >> +	       pgprot_val(powerpc_vm_get_page_prot(vm_flags)));
> > Any reason to keep powerpc_vm_get_page_prot() rather than open code it
> > here?
> > 
> > This applies to other architectures that implement arch_vm_get_page_prot()
> > and/or arch_filter_pgprot() as well.
> 
> Just to minimize the code churn ! But I will be happy to open code them
> here (and in other platforms) if that will be preferred.

I think this will be clearer because all the processing will be at one place.
Besides, this way include/asm/pgtable.h becomes shorter and less crowded.

-- 
Sincerely yours,
Mike.