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Date:   Wed, 28 May 2014 18:24:04 +0200
From:   Paolo Bonzini <pbonzini@redhat.com>
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To:     James Hogan <james.hogan@imgtec.com>,
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CC:     linux-mips@linux-mips.org, Gleb Natapov <gleb@kernel.org>,
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        qemu-devel <qemu-devel@nongnu.org>
Subject: Re: [PATCH 14/21] MIPS: KVM: Add nanosecond count bias KVM register
References: <1398439204-26171-1-git-send-email-james.hogan@imgtec.com> <1398439204-26171-15-git-send-email-james.hogan@imgtec.com> <535A9AF5.30105@gmail.com> <2197488.6tnytXFBJm@radagast> <535B7E58.4070304@redhat.com> <5385F0E4.1080207@imgtec.com>
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Il 28/05/2014 16:21, James Hogan ha scritto:
> The implementation in QEMU that I've settled upon makes do with just
> COUNT_CTL and COUNT_RESUME, but with a slight kernel modification so
> that COUNT_RESUME is writeable (to any positive monotonic nanosecond
> value <= now). It works fairly cleanly and correctly even with stopping
> and starting VM clock (gdb, stop/cont, savevm/loadvm, live migration),
> to match the behaviour of the existing mips cpu timer emulation, so I
> plan to drop this bias patch, and will post a v2 patchset soon with just
> a few modifications.

It makes sense to have writable registers in the emulator, even if they 
are read-only in real hardware.  We also do that for x86, FWIW.

So the idea looks okay to me.

Paolo