[PATCH v4 13/29] arm64: convert protection key into vm_flags and pgprot values

[Dave Martin]

On Thu, Aug 01, 2024 at 11:55:02AM +0100, Joey Gouly wrote:
> On Thu, Jul 25, 2024 at 04:49:50PM +0100, Dave Martin wrote:
> > On Fri, May 03, 2024 at 02:01:31PM +0100, Joey Gouly wrote:
> > > Modify arch_calc_vm_prot_bits() and vm_get_page_prot() such that the pkey
> > > value is set in the vm_flags and then into the pgprot value.
> > > 
> > > Signed-off-by: Joey Gouly <joey.gouly at arm.com>
> > > Cc: Catalin Marinas <catalin.marinas at arm.com>
> > > Cc: Will Deacon <will at kernel.org>
> > > ---
> > >  arch/arm64/include/asm/mman.h | 8 +++++++-
> > >  arch/arm64/mm/mmap.c          | 9 +++++++++
> > >  2 files changed, 16 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
> > > index 5966ee4a6154..ecb2d18dc4d7 100644
> > > --- a/arch/arm64/include/asm/mman.h
> > > +++ b/arch/arm64/include/asm/mman.h
> > > @@ -7,7 +7,7 @@
> > >  #include <uapi/asm/mman.h>
> > >  
> > >  static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
> > > -	unsigned long pkey __always_unused)
> > > +	unsigned long pkey)
> > >  {
> > >  	unsigned long ret = 0;
> > >  
> > > @@ -17,6 +17,12 @@ static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
> > >  	if (system_supports_mte() && (prot & PROT_MTE))
> > >  		ret |= VM_MTE;
> > >  
> > > +#if defined(CONFIG_ARCH_HAS_PKEYS)
> > > +	ret |= pkey & 0x1 ? VM_PKEY_BIT0 : 0;
> > > +	ret |= pkey & 0x2 ? VM_PKEY_BIT1 : 0;
> > > +	ret |= pkey & 0x4 ? VM_PKEY_BIT2 : 0;
> > 
> > Out of interest, is this as bad as it looks or does the compiler turn
> > it into a shift and mask?
> 
> Yeah, (gcc 13.2) produces good code here (this is do_mprotect_pkey after removing a lot of branching):
> 
> 	and     w0, w0, #0x7
> 	orr     x1, x1, x0, lsl #32

Neat, good ol' gcc!

Cheers
---Dave