diff mbox series

[v4,24/25] KVM: VMX: Cache MSR_IA32_VMX_MISC in vmcs_config

Message ID 20220714091327.1085353-25-vkuznets@redhat.com (mailing list archive)
State New, archived
Headers show
Series KVM: VMX: Support updated eVMCSv1 revision + use vmcs_config for L1 VMX MSRs | expand

Commit Message

Vitaly Kuznetsov July 14, 2022, 9:13 a.m. UTC 
Like other host VMX control MSRs, MSR_IA32_VMX_MISC can be cached in
vmcs_config to avoid the need to re-read it later, e.g. from
cpu_has_vmx_intel_pt() or cpu_has_vmx_shadow_vmcs().

No (real) functional change intended.

Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/vmx/capabilities.h | 11 +++--------
 arch/x86/kvm/vmx/vmx.c          |  8 +++++---
 2 files changed, 8 insertions(+), 11 deletions(-)

Comments

Sean Christopherson July 21, 2022, 11:06 p.m. UTC | #1 
On Thu, Jul 14, 2022, Vitaly Kuznetsov wrote:
> @@ -2613,6 +2614,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>  	if (((vmx_msr_high >> 18) & 15) != 6)
>  		return -EIO;
>  
> +	rdmsrl(MSR_IA32_VMX_MISC, misc_msr);

Might make sense to sanitize fields that KVM doesn't use and that are not exposed
to L1.  Not sure it's worthwhile though as many of the bits fall into a grey area,
e.g. all the SMM stuff isn't technically used by KVM, but that's largely because
much of it just isn't relevant to virtualization.

I'm totally ok leaving it as-is, though maybe name it "unsanitized_misc" or so
to make that obvious?

>  	vmcs_conf->size = vmx_msr_high & 0x1fff;
>  	vmcs_conf->basic_cap = vmx_msr_high & ~0x1fff;
>  
> @@ -2624,6 +2627,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>  	vmcs_conf->cpu_based_3rd_exec_ctrl = _cpu_based_3rd_exec_control;
>  	vmcs_conf->vmexit_ctrl         = _vmexit_control;
>  	vmcs_conf->vmentry_ctrl        = _vmentry_control;
> +	vmcs_conf->misc	= misc_msr;
>  
>  	return 0;
>  }
> @@ -8241,11 +8245,9 @@ static __init int hardware_setup(void)
>  
>  	if (enable_preemption_timer) {
>  		u64 use_timer_freq = 5000ULL * 1000 * 1000;
> -		u64 vmx_msr;
>  
> -		rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
>  		cpu_preemption_timer_multi =
> -			vmx_msr & VMX_MISC_PREEMPTION_TIMER_RATE_MASK;
> +			vmcs_config.misc & VMX_MISC_PREEMPTION_TIMER_RATE_MASK;
>  
>  		if (tsc_khz)
>  			use_timer_freq = (u64)tsc_khz * 1000;
> -- 
> 2.35.3
>
Vitaly Kuznetsov Aug. 2, 2022, 4:11 p.m. UTC | #2 
Sean Christopherson <seanjc@google.com> writes:

> On Thu, Jul 14, 2022, Vitaly Kuznetsov wrote:
>> @@ -2613,6 +2614,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>>  	if (((vmx_msr_high >> 18) & 15) != 6)
>>  		return -EIO;
>>  
>> +	rdmsrl(MSR_IA32_VMX_MISC, misc_msr);
>
> Might make sense to sanitize fields that KVM doesn't use and that are not exposed
> to L1.  Not sure it's worthwhile though as many of the bits fall into a grey area,
> e.g. all the SMM stuff isn't technically used by KVM, but that's largely because
> much of it just isn't relevant to virtualization.
>
> I'm totally ok leaving it as-is, though maybe name it "unsanitized_misc" or so
> to make that obvious?

I couldn't convince myself to add 'unsanitized_' prefix as I don't think
it significantly reduces possible confusion (the quiestion would be
'sanitized for what and in which way?') so a need for 'git grep' seems
imminent anyway. Hope I've addressed the rest of your comments in v5
though, thanks for your review!
Sean Christopherson Aug. 2, 2022, 4:28 p.m. UTC | #3 
On Tue, Aug 02, 2022, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@google.com> writes:
> 
> > On Thu, Jul 14, 2022, Vitaly Kuznetsov wrote:
> >> @@ -2613,6 +2614,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
> >>  	if (((vmx_msr_high >> 18) & 15) != 6)
> >>  		return -EIO;
> >>  
> >> +	rdmsrl(MSR_IA32_VMX_MISC, misc_msr);
> >
> > Might make sense to sanitize fields that KVM doesn't use and that are not exposed
> > to L1.  Not sure it's worthwhile though as many of the bits fall into a grey area,
> > e.g. all the SMM stuff isn't technically used by KVM, but that's largely because
> > much of it just isn't relevant to virtualization.
> >
> > I'm totally ok leaving it as-is, though maybe name it "unsanitized_misc" or so
> > to make that obvious?
> 
> I couldn't convince myself to add 'unsanitized_' prefix as I don't think
> it significantly reduces possible confusion (the quiestion would be
> 'sanitized for what and in which way?') so a need for 'git grep' seems
> imminent anyway.

Yeah, no objection to leaving it alone.  VMX_MISC is such an oddball MSR that it
practically comes with disclaimers anyways :-)
diff mbox series

Patch

diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index 07e7492fe72a..07f7a9534211 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -65,6 +65,7 @@  struct vmcs_config {
 	u64 cpu_based_3rd_exec_ctrl;
 	u32 vmexit_ctrl;
 	u32 vmentry_ctrl;
+	u64 misc;
 	struct nested_vmx_msrs nested;
 };
 extern struct vmcs_config vmcs_config;
@@ -225,11 +226,8 @@  static inline bool cpu_has_vmx_vmfunc(void)
 
 static inline bool cpu_has_vmx_shadow_vmcs(void)
 {
-	u64 vmx_msr;
-
 	/* check if the cpu supports writing r/o exit information fields */
-	rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
-	if (!(vmx_msr & MSR_IA32_VMX_MISC_VMWRITE_SHADOW_RO_FIELDS))
+	if (!(vmcs_config.misc & MSR_IA32_VMX_MISC_VMWRITE_SHADOW_RO_FIELDS))
 		return false;
 
 	return vmcs_config.cpu_based_2nd_exec_ctrl &
@@ -371,10 +369,7 @@  static inline bool cpu_has_vmx_invvpid_global(void)
 
 static inline bool cpu_has_vmx_intel_pt(void)
 {
-	u64 vmx_msr;
-
-	rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
-	return (vmx_msr & MSR_IA32_VMX_MISC_INTEL_PT) &&
+	return (vmcs_config.misc & MSR_IA32_VMX_MISC_INTEL_PT) &&
 		(vmcs_config.cpu_based_2nd_exec_ctrl & SECONDARY_EXEC_PT_USE_GPA) &&
 		(vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_RTIT_CTL);
 }
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 35285109856f..ab091758c437 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2479,6 +2479,7 @@  static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 	u64 _cpu_based_3rd_exec_control = 0;
 	u32 _vmexit_control = 0;
 	u32 _vmentry_control = 0;
+	u64 misc_msr;
 	int i;
 
 	/*
@@ -2613,6 +2614,8 @@  static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 	if (((vmx_msr_high >> 18) & 15) != 6)
 		return -EIO;
 
+	rdmsrl(MSR_IA32_VMX_MISC, misc_msr);
+
 	vmcs_conf->size = vmx_msr_high & 0x1fff;
 	vmcs_conf->basic_cap = vmx_msr_high & ~0x1fff;
 
@@ -2624,6 +2627,7 @@  static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 	vmcs_conf->cpu_based_3rd_exec_ctrl = _cpu_based_3rd_exec_control;
 	vmcs_conf->vmexit_ctrl         = _vmexit_control;
 	vmcs_conf->vmentry_ctrl        = _vmentry_control;
+	vmcs_conf->misc	= misc_msr;
 
 	return 0;
 }
@@ -8241,11 +8245,9 @@  static __init int hardware_setup(void)
 
 	if (enable_preemption_timer) {
 		u64 use_timer_freq = 5000ULL * 1000 * 1000;
-		u64 vmx_msr;
 
-		rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
 		cpu_preemption_timer_multi =
-			vmx_msr & VMX_MISC_PREEMPTION_TIMER_RATE_MASK;
+			vmcs_config.misc & VMX_MISC_PREEMPTION_TIMER_RATE_MASK;
 
 		if (tsc_khz)
 			use_timer_freq = (u64)tsc_khz * 1000;