Re: [PATCH RFC V2 02/17] x86/fpu: Refactor arch_set_user_pkey_access() for PKS support

On Fri, Jul 17, 2020 at 12:20:41AM -0700, ira.weiny@intel.com wrote:

+/*

• • Get a new pkey register value from the user values specified.
• • Kernel users use the same flags as user space:

• • PKEY_DISABLE_ACCESS
    

• • PKEY_DISABLE_WRITE
    

• */

+u32 get_new_pkr(u32 old_pkr, int pkey, unsigned long init_val) +{

• int pkey_shift = (pkey * PKR_BITS_PER_PKEY);
• u32 new_pkr_bits = 0;
• /* Set the bits we need in the register: */
• if (init_val & PKEY_DISABLE_ACCESS)

• new_pkr_bits |= PKR_AD_BIT;
  

• if (init_val & PKEY_DISABLE_WRITE)

• new_pkr_bits |= PKR_WD_BIT;
  

• /* Shift the bits in to the correct place: */
• new_pkr_bits <<= pkey_shift;
• /* Mask off any old bits in place: */
• old_pkr &= ~((PKR_AD_BIT | PKR_WD_BIT) << pkey_shift);
• /* Return the old part along with the new part: */
• return old_pkr | new_pkr_bits;

+}

This is unbelievable junk...

How about something like:

u32 update_pkey_reg(u32 pk_reg, int pkey, unsigned int flags) { int pkey_shift = pkey * PKR_BITS_PER_PKEY;

pk_reg &= ~(((1 << PKR_BITS_PER_PKEY) - 1) << pkey_shift);

if (flags & PKEY_DISABLE_ACCESS) pk_reg |= PKR_AD_BIT << pkey_shift; if (flags & PKEY_DISABLE_WRITE) pk_reg |= PKR_WD_BIT << pkey_shift;

return pk_reg; }

Then we at least have a little clue wtf the thing does.. Yes I started with a rename and then got annoyed at the implementation too.