Re: [PATCH 22/26] KVM: PPC: Book3S PR: add emulation for trechkpt in PR KVM.

Hi Paul,
On Tue, Jan 23, 2018 at 08:36:44PM +1100, Paul Mackerras wrote:

On Thu, Jan 11, 2018 at 06:11:35PM +0800, wei.guo.simon@gmail.com wrote:

quoted

From: Simon Guo <redacted>

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 <redacted>

[snip]

quoted

+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.

I will rework and remove "save_msr_tm" from the code.

Thanks,
- Simon