From: "Radim Krčmář" <rkrcmar@redhat.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: kvm-devel <kvm@vger.kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
pagupta@redhat.com
Subject: Re: [PATCH] KVM: x86: remove irq disablement around KVM_SET_CLOCK/KVM_GET_CLOCK
Date: Wed, 12 Apr 2017 19:40:51 +0200 [thread overview]
Message-ID: <20170412174051.GB23556@potion> (raw)
In-Reply-To: <20170412172313.GA26589@amt.cnet>
2017-04-12 14:23-0300, Marcelo Tosatti:
> The disablement of interrupts at KVM_SET_CLOCK/KVM_GET_CLOCK
> attempts to disable interrupts in that section to protect
> the values that are calculated in that section from interrupt interference.
>
> now_ns is calculated inside the irq protected region,
> user_ns.clock is passed from userspace (therefore not susceptible
> to interrupt variation).
>
> About the line
> now_ns = __get_kvmclock_ns(kvm); (1)
>
> Interrupts can happen afterwards local_irq_enable(),
> rendering "now_ns" relative to its execution time PLUS
> interrupt time.
>
> Therefore the local_irq_disable() / local_irq_enable() protection is not
> necessary (that is: interrupts triggering after local_irq_enable cause
> the same problem that the protection is trying to avoid).
Makes sense.
get_kvmclock_ns() has the same problem and this patch should cover it as
well.
next prev parent reply other threads:[~2017-04-12 17:41 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-12 17:23 [PATCH] KVM: x86: remove irq disablement around KVM_SET_CLOCK/KVM_GET_CLOCK Marcelo Tosatti
2017-04-12 17:40 ` Radim Krčmář [this message]
2017-04-13 6:06 ` Pankaj Gupta
2017-04-13 18:30 ` Marcelo Tosatti
2017-04-13 18:49 ` [PATCH v2] " Marcelo Tosatti
2017-04-17 11:05 ` Pankaj Gupta
2017-04-17 15:51 ` [PATCH v3] " Marcelo Tosatti
2017-04-18 5:06 ` Pankaj Gupta
2017-04-21 10:04 ` Paolo Bonzini
2017-04-13 7:32 ` [PATCH] " Roman Kagan
2017-04-13 13:27 ` Radim Krčmář
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