linux-kernel - Re: [PATCH] x86: vdso: fix pvclock races with task migration

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Message-ID: <20150407124736.GA2637@potion.brq.redhat.com>
Date:	Tue, 7 Apr 2015 14:47:36 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Andy Lutomirski <luto@...capital.net>, stable@...r.kernel.org
Subject: Re: [PATCH] x86: vdso: fix pvclock races with task migration

2015-04-07 13:11+0200, Paolo Bonzini:
> On 02/04/2015 20:44, Radim Krčmář wrote:
> > If we were migrated right after __getcpu, but before reading the
> > migration_count, we wouldn't notice that we read TSC of a different
> > VCPU, nor that KVM's bug made pvti invalid, as only migration_count
> > on source VCPU is increased.
> > 
> > Change vdso instead of updating migration_count on destination.
> > 
> > Fixes: 0a4e6be9ca17 ("x86: kvm: Revert "remove sched notifier for cross-cpu migrations"")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> 
> Applying this, but removing the "Fixes" tag because a guest patch cannot
> fix a host patch (it can work around it or complement it).

I think it was correct.  Both are guest only, the revert just missed
some races.  (0a4e6be9ca17 has misleading commit message ...)
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