[PATCH v13 10/24] selftests/vm: clear the bits in shadow reg when a pkey is freed.

[Dave Hansen]

On 06/13/2018 05:45 PM, Ram Pai wrote:
> When a key is freed, the  key  is  no  more  effective.
> Clear the bits corresponding to the pkey in the shadow
> register. Otherwise  it  will carry some spurious bits
> which can trigger false-positive asserts.
...--- a/tools/testing/selftests/vm/protection_keys.c
> +++ b/tools/testing/selftests/vm/protection_keys.c
> @@ -556,6 +556,9 @@ int alloc_pkey(void)
>  int sys_pkey_free(unsigned long pkey)
>  {
>  	int ret = syscall(SYS_pkey_free, pkey);
> +
> +	if (!ret)
> +		shadow_pkey_reg &= clear_pkey_flags(pkey, PKEY_DISABLE_ACCESS);
>  	dprintf1("%s(pkey=%ld) syscall ret: %d\n", __func__, pkey, ret);
>  	return ret;
>  }

This would be great code for an actual application.  But, I'm not
immediately convinced we want sane, kind behavior in our selftest.  x86
doesn't clear the hardware register at pkey_free, so wouldn't this cause
the shadow and the hardware register to diverge?