From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH v7 08/12] ARM: KVM: World-switch implementation
Date: Wed, 28 Mar 2012 15:05:55 +0200
Message-ID: <4F730CB3.6010402@redhat.com>
References: <20120312065134.8074.36949.stgit@ubuntu> <20120312065241.8074.44277.stgit@ubuntu> <87wr6c88s3.fsf@rustcorp.com.au>
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Cc: Christoffer Dall <c.dall@virtualopensystems.com>,
	android-virt@lists.cs.columbia.edu, kvm@vger.kernel.org,
	Peter Maydell <peter.maydell@linaro.org>,
	tech@virtualopensystems.com
To: Rusty Russell <rusty.russell@linaro.org>
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On 03/23/2012 02:23 AM, Rusty Russell wrote:
> On Mon, 12 Mar 2012 02:52:41 -0400, Christoffer Dall <c.dall@virtualopensystems.com> wrote:
> > @@ -236,6 +237,24 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
> >  
> >  int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
> >  {
> > +	unsigned long cpsr;
> > +	unsigned long sctlr;
> > +
> > +
> > +	/* Init execution CPSR */
> > +	asm volatile ("mrs	%[cpsr], cpsr" :
> > +			[cpsr] "=r" (cpsr));
> > +	vcpu->arch.regs.cpsr = SVC_MODE | PSR_I_BIT | PSR_F_BIT | PSR_A_BIT |
> > +				(cpsr & PSR_E_BIT);
> > +
> > +	/* Init SCTLR with MMU disabled */
> > +	asm volatile ("mrc	p15, 0, %[sctlr], c1, c0, 0" :
> > +			[sctlr] "=r" (sctlr));
> > +	vcpu->arch.cp15[c1_SCTLR] = sctlr & ~1U;
> > +
> > +	/* Compute guest MPIDR */
> > +	vcpu->arch.cp15[c0_MPIDR] = (read_cpuid_mpidr() & ~0xff)
> > +				    | vcpu->vcpu_id;
> >  	return 0;
> >  }
>
> Hi Christoffer!
>
>         I started cleaning this up, on the theory that we should use the
> defined reset values rather than basing them on host values.  Then I
> discovered that this is ignored by qemu anyway, which overrides the
> values (except for MPIDR: I set that to 0x80000000 | vcpu->vcpu_id,
> which seems correct to me).
>
> Should this code be dropped altogether?  Peter points out that once we
> add new regs, they *must* be initialized to correct reset values in case
> older QEMU knows nothing about them, but for the rest it just seems
> confusing...
>

It's best to initialize everything.  As far as this code is concerned
qemu is just another user and we shouldn't rely on its implementation.

-- 
error compiling committee.c: too many arguments to function