linux-kernel - Re: [PATCH v12 08/22] selftests/vm: clear the bits in shadow reg when a pkey is freed.

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Date:   Fri, 16 Mar 2018 15:10:07 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Ram Pai <linuxram@...ibm.com>, shuahkh@....samsung.com,
        linux-kselftest@...r.kernel.org
Cc:     mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org, x86@...nel.org, linux-arch@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, akpm@...ux-foundation.org,
        benh@...nel.crashing.org, paulus@...ba.org,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, hbabu@...ibm.com, mhocko@...nel.org,
        bauerman@...ux.vnet.ibm.com, ebiederm@...ssion.com, arnd@...db.de
Subject: Re: [PATCH v12 08/22] selftests/vm: clear the bits in shadow reg when
 a pkey is freed.

On 02/21/2018 05:55 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.
...
> diff --git a/tools/testing/selftests/vm/protection_keys.c b/tools/testing/selftests/vm/protection_keys.c
> index ca54a95..aaf9f09 100644
> --- a/tools/testing/selftests/vm/protection_keys.c
> +++ b/tools/testing/selftests/vm/protection_keys.c
> @@ -582,6 +582,9 @@ int alloc_pkey(void)
>  int sys_pkey_free(unsigned long pkey)
>  {
>  	int ret = syscall(SYS_pkey_free, pkey);
> +
> +	if (!ret)
> +		shadow_pkey_reg &= reset_bits(pkey, PKEY_DISABLE_ACCESS);
>  	dprintf1("%s(pkey=%ld) syscall ret: %d\n", __func__, pkey, ret);
>  	return ret;
>  }

Did this cause problems for you in practice?

On x86, sys_pkey_free() does not affect PKRU, so this isn't quite right.
 I'd much rather have the actual tests explicitly clear the PKRU bits
and also in the process clear the shadow bits.