linux-kernel - Re: [PATCH 7/9] KVM, VMX: add support for switching of PERF_GLOBAL

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Date:	Tue, 4 Oct 2011 11:57:26 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	joerg.roedel@....com, mingo@...e.hu, a.p.zijlstra@...llo.nl
Subject: Re: [PATCH 7/9] KVM, VMX: add support for switching of
 PERF_GLOBAL_CTRL

On Tue, Oct 04, 2011 at 11:32:03AM +0200, Avi Kivity wrote:
> On 10/03/2011 03:49 PM, Gleb Natapov wrote:
> >Some cpus have special support for switching PERF_GLOBAL_CTRL msr.
> >Add logic to detect if such support exists and works properly and extend
> >msr switching code to use it if available. Also extend number of generic
> >msr switching entries to 8.
> >
> >
> >  static DECLARE_BITMAP(vmx_vpid_bitmap, VMX_NR_VPIDS);
> >  static DEFINE_SPINLOCK(vmx_vpid_lock);
> >@@ -1195,10 +1196,29 @@ static void clear_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr)
> >  {
> >  	unsigned i;
> >  	struct msr_autoload *m =&vmx->msr_autoload;
> >+	u32 entry_load, exit_load;
> >+	bool done = false;
> >
> >-	if (msr == MSR_EFER&&  cpu_has_load_ia32_efer) {
> >-		vmcs_clear_bits(VM_ENTRY_CONTROLS, VM_ENTRY_LOAD_IA32_EFER);
> >-		vmcs_clear_bits(VM_EXIT_CONTROLS, VM_EXIT_LOAD_IA32_EFER);
> >+	switch (msr) {
> >+	case MSR_EFER:
> >+		if (cpu_has_load_ia32_efer) {
> >+			entry_load = VM_ENTRY_LOAD_IA32_EFER;
> >+			exit_load = VM_EXIT_LOAD_IA32_EFER;
> >+			done = true;
> >+		}
> >+		break;
> >+	case MSR_CORE_PERF_GLOBAL_CTRL:
> >+		if (cpu_has_load_perf_global_ctrl) {
> >+			entry_load = VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
> >+			exit_load = VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL;
> >+			done = true;
> >+		}
> >+		break;
> >+	}
> >+
> >+	if (done) {
> >+		vmcs_clear_bits(VM_ENTRY_CONTROLS, entry_load);
> >+		vmcs_clear_bits(VM_EXIT_CONTROLS, exit_load);
> >  		return;
> >  	}
> >
> >
> 
> This is ugly.  How about
> 
>    if (msr == MSR_EFER && cpu_has_load_ia32_efer) {
>        clear_atomic_switch_msr_special(VM_ENTRY_LOAD_IA32_EFER,
> VM_EXIT_LOAD_IA32_EFER);
>        return;
>    }
> 
> avoids the fake 'done' variable.
> 
OK.

--
			Gleb.
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