lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Tue, 19 Sep 2017 10:25:11 +0200 From: Christian Borntraeger <borntraeger@...ibm.com> To: Paolo Bonzini <pbonzini@...hat.com>, Davidlohr Bueso <dave@...olabs.net>, mingo@...nel.org, peterz@...radead.org Cc: npiggin@...il.com, paulmck@...ux.vnet.ibm.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, Cornelia Huck <cohuck@...hat.com> Subject: Re: [PATCH v2 0/7] swait: Introduce and use swq_has_sleeper() On 09/15/2017 01:53 PM, Paolo Bonzini wrote: > On 13/09/2017 22:08, Davidlohr Bueso wrote: >> The following patches fix and/or justify (in baby steps) some of the >> callers. The main exception is s390, which I didn't follow how ->valid_wakeup >> can get hoisted as kvm_vcpu_block does not use that in the wait loop. > > valid_wakeup is just an optimization, so it's not a problem. > > There seems to be always an atomic_or or set_bit before > kvm_s390_vcpu_wakeup is called (except kvm_s390_idle_wakeup which has no > store at all and doesn't need any serialization). So my suggestion is > to add an smp__mb_after_atomic in kvm_s390_vcpu_wakeup; I'll let the > s390 guys do it. I will queue something like this diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c index a832ad0..44239b5 100644 --- a/arch/s390/kvm/interrupt.c +++ b/arch/s390/kvm/interrupt.c @@ -1074,6 +1074,12 @@ void kvm_s390_vcpu_wakeup(struct kvm_vcpu *vcpu) * in kvm_vcpu_block without having the waitqueue set (polling) */ vcpu->valid_wakeup = true; + /* + * This is mostly to document, that the read in swait_active could + * be moved before other stores, leading to subtle races. + * All current users do not store or use an atomic like update + */ + __smp_mb__after_atomic(); if (swait_active(&vcpu->wq)) { /* * The vcpu gave up the cpu voluntarily, mark it as a good but I am asking myself if it is "safer" to make this function use swq_has_sleepers in case we add in a distant future another user to kvm_s390_vcpu_wakeup that does use a normal store and everybody has already forgotten this?
Powered by blists - more mailing lists