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Date: Tue, 23 Jan 2018 20:36:44 +1100
From: Paul Mackerras <paulus@ozlabs.org>
To: wei.guo.simon@gmail.com
Cc: linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org
Subject: Re: [PATCH 22/26] KVM: PPC: Book3S PR: add emulation for trechkpt in
 PR KVM.
Message-ID: <20180123093644.GN3924@fergus.ozlabs.ibm.com>
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On Thu, Jan 11, 2018 at 06:11:35PM +0800, wei.guo.simon@gmail.com wrote:
> From: Simon Guo <wei.guo.simon@gmail.com>
> 
> This patch adds host emulation when guest PR KVM executes "trechkpt.",
> which is a privileged instruction and will trap into host.
> 
> We firstly copy vcpu ongoing content into vcpu tm checkpoint
> content, then perform kvmppc_restore_tm_pr() to do trechkpt.
> with updated vcpu tm checkpoint vals.
> 
> Signed-off-by: Simon Guo <wei.guo.simon@gmail.com>

[snip]

> +static void kvmppc_emulate_trchkpt(struct kvm_vcpu *vcpu)
> +{
> +	unsigned long guest_msr = kvmppc_get_msr(vcpu);
> +
> +	preempt_disable();
> +	vcpu->arch.save_msr_tm = MSR_TS_S;
> +	vcpu->arch.save_msr_tm &= ~(MSR_FP | MSR_VEC | MSR_VSX);

This looks odd, since you are clearing bits when you have just set
save_msr_tm to a constant value that doesn't have these bits set.
This could be taken as a sign that the previous line has a bug and you
meant "|=" or something similar instead of "=".  I think you probably
did mean "=", in which case you should remove the line clearing
FP/VEC/VSX.

Paul.