From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: KVM: x86: relax MSR_KVM_SYSTEM_TIME alignment check
Date: Fri, 22 Mar 2013 16:47:35 -0300
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 <20130322192100.GA9382@redhat.com>
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Cc: Andy Honig <ahonig@google.com>, kvm <kvm@vger.kernel.org>
To: Gleb Natapov <gleb@redhat.com>
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On Fri, Mar 22, 2013 at 09:21:00PM +0200, Gleb Natapov wrote:
> On Fri, Mar 22, 2013 at 04:14:07PM -0300, Marcelo Tosatti wrote:
> > 
> > RHEL5 i386 guests register non 32-byte aligned addresses:
> > 
> > kvm-clock: cpu 1, msr 0:3018aa5, secondary cpu clock
> > kvm-clock: cpu 2, msr 0:301f8e9, secondary cpu clock
> > kvm-clock: cpu 3, msr 0:302672d, secondary cpu clock
> > 
> > Check for an address+len that would cross page boundary
> > instead.
> > 
> Ugh. Is there guaranty that it will not register a memory region that
> crosses page boundary or it is pure luck that this does not happen?

Pure build time luck - there is no guarantee that percpu data will not
cross page boundary AFAIK.