From: Heiko Carstens <hca@linux.ibm.com>
To: Nico Boehr <nrb@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>,
Janis Schoetterl-Glausch <scgl@linux.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
David Hildenbrand <david@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
kvm@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-s390@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Shuah Khan <shuah@kernel.org>,
Sven Schnelle <svens@linux.ibm.com>
Subject: Re: [PATCH v2 1/9] s390/uaccess: Add storage key checked cmpxchg access to user space
Date: Fri, 21 Oct 2022 21:22:45 +0200 [thread overview]
Message-ID: <Y1LxhaZaVZlM0Cl/@osiris> (raw)
In-Reply-To: <166627325676.27216.13358887886569042677@t14-nrb>
On Thu, Oct 20, 2022 at 03:40:56PM +0200, Nico Boehr wrote:
> Quoting Janis Schoetterl-Glausch (2022-10-12 22:56:01)
> > + "2: lr %[old_word],%[tmp]\n"
> > + "3: cs %[tmp],%[new_word],%[aligned]\n"
> > + "4: jnl 5f\n"
> > + /* We'll restore old_word before the cs, use reg for the diff */
> > + " xr %[old_word],%[tmp]\n"
> > + /* Apply diff assuming only bits outside target byte(s) changed */
> > + " xr %[new_word],%[old_word]\n"
> > + /* If prior assumption false we exit loop, so not an issue */
> > + " nr %[old_word],%[mask]\n"
> > + " jz 2b\n"
>
> So if the remainder changed but the actual value to exchange stays the same, we
> loop in the kernel. Does it maybe make sense to limit the number of iterations
> we spend retrying? I think while looping here the calling process can't be
> killed, can it?
Yes, the number of loops should be limited; quite similar what arm64
implemented with commit 03110a5cb216 ("arm64: futex: Bound number of
LDXR/STXR loops in FUTEX_WAKE_OP").
next prev parent reply other threads:[~2022-10-21 19:23 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-12 20:56 [PATCH v2 0/9] KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg Janis Schoetterl-Glausch
2022-10-12 20:56 ` [PATCH v2 1/9] s390/uaccess: Add storage key checked cmpxchg access to user space Janis Schoetterl-Glausch
2022-10-20 11:18 ` Heiko Carstens
2022-10-20 13:40 ` Nico Boehr
2022-10-21 19:22 ` Heiko Carstens [this message]
2022-11-02 14:12 ` Heiko Carstens
2022-11-02 14:16 ` [PATCH 1/5] s390/cmpxchg: use symbolic names for inline assembly operands Heiko Carstens
2022-11-02 14:17 ` [PATCH 2/5] s390/cmpxchg: make variables local to each case label Heiko Carstens
2022-11-02 14:18 ` [PATCH 3/5] s390/cmpxchg: remove digits from input constraints Heiko Carstens
2022-11-02 14:18 ` [PATCH 4/5] s390/extable: add EX_TABLE_UA_LOAD_REGPAIR() macro Heiko Carstens
2022-11-02 14:19 ` [PATCH 5/5] s390/uaccess: add cmpxchg_user_key() Heiko Carstens
2022-11-09 15:46 ` Janis Schoetterl-Glausch
2022-11-09 22:24 ` Heiko Carstens
2022-11-10 11:01 ` Janis Schoetterl-Glausch
2022-11-10 11:32 ` Heiko Carstens
2022-11-13 18:20 ` Heiko Carstens
2022-11-16 14:47 ` [PATCH] s390: cmpxchg: Make loop condition for 1,2 byte cases precise Janis Schoetterl-Glausch
2022-11-17 18:19 ` Heiko Carstens
2022-11-16 19:36 ` [PATCH v2 1/9] s390/uaccess: Add storage key checked cmpxchg access to user space Janis Schoetterl-Glausch
2022-11-17 8:42 ` Nico Boehr
2022-11-17 10:07 ` [RFC PATCH] s390/uaccess: Limit number of retries for cmpxchg_user_key Janis Schoetterl-Glausch
2022-11-17 18:20 ` Heiko Carstens
2022-10-12 20:56 ` [PATCH v2 2/9] KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg Janis Schoetterl-Glausch
2022-10-13 13:48 ` kernel test robot
2022-10-12 20:56 ` [PATCH v2 3/9] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F_CMPXCHG Janis Schoetterl-Glausch
2022-10-12 20:56 ` [PATCH v2 4/9] KVM: s390: selftest: memop: Pass mop_desc via pointer Janis Schoetterl-Glausch
2022-10-12 20:56 ` [PATCH v2 5/9] KVM: s390: selftest: memop: Replace macros by functions Janis Schoetterl-Glausch
2022-10-12 20:56 ` [PATCH v2 6/9] KVM: s390: selftest: memop: Add cmpxchg tests Janis Schoetterl-Glausch
2022-10-12 20:56 ` [PATCH v2 7/9] KVM: s390: selftest: memop: Add bad address test Janis Schoetterl-Glausch
2022-10-13 13:17 ` Nico Boehr
2022-10-12 20:56 ` [PATCH v2 8/9] KVM: s390: selftest: memop: Fix typo Janis Schoetterl-Glausch
2022-10-13 13:16 ` Nico Boehr
2022-10-12 20:56 ` [PATCH v2 9/9] KVM: s390: selftest: memop: Fix wrong address being used in test Janis Schoetterl-Glausch
2022-10-13 13:15 ` Nico Boehr
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