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

[Joey Gouly]

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

> 
> 
> > +#endif
> > +
> >  	return ret;
> >  }
> >  #define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
> > diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> > index 642bdf908b22..86eda6bc7893 100644
> > --- a/arch/arm64/mm/mmap.c
> > +++ b/arch/arm64/mm/mmap.c
> > @@ -102,6 +102,15 @@ pgprot_t vm_get_page_prot(unsigned long vm_flags)
> >  	if (vm_flags & VM_MTE)
> >  		prot |= PTE_ATTRINDX(MT_NORMAL_TAGGED);
> >  
> > +#ifdef CONFIG_ARCH_HAS_PKEYS
> > +	if (vm_flags & VM_PKEY_BIT0)
> > +		prot |= PTE_PO_IDX_0;
> > +	if (vm_flags & VM_PKEY_BIT1)
> > +		prot |= PTE_PO_IDX_1;
> > +	if (vm_flags & VM_PKEY_BIT2)
> > +		prot |= PTE_PO_IDX_2;
> > +#endif
> > +
> 
> Ditto.  At least we only have three bits to cope with either way.
> 
> I'm guessing that these functions are not super-hot path.
> 
> [...]
> 
> Cheers
> ---Dave