diff mbox series

[43/61] KVM: x86: Use KVM cpu caps to mark CR4.LA57 as not-reserved

Message ID 20200201185218.24473-44-sean.j.christopherson@intel.com
State New, archived
Headers show
Series KVM: x86: Introduce KVM cpu caps | expand

Commit Message

Sean Christopherson Feb. 1, 2020, 6:52 p.m. UTC
Add accessor(s) for KVM cpu caps and use said accessor to detect
hardware support for LA57 instead of manually querying CPUID.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/cpuid.h | 13 +++++++++++++
 arch/x86/kvm/x86.c   |  2 +-
 2 files changed, 14 insertions(+), 1 deletion(-)

Comments

Vitaly Kuznetsov Feb. 24, 2020, 10:08 p.m. UTC | #1
Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Add accessor(s) for KVM cpu caps and use said accessor to detect
> hardware support for LA57 instead of manually querying CPUID.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kvm/cpuid.h | 13 +++++++++++++
>  arch/x86/kvm/x86.c   |  2 +-
>  2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index 7b71ae0ca05e..5ce4219d465f 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -274,6 +274,19 @@ static __always_inline void kvm_cpu_cap_set(unsigned x86_feature)
>  	kvm_cpu_caps[x86_leaf] |= __feature_bit(x86_feature);
>  }
>  
> +static __always_inline u32 kvm_cpu_cap_get(unsigned x86_feature)
> +{
> +	unsigned x86_leaf = x86_feature / 32;
> +
> +	reverse_cpuid_check(x86_leaf);
> +	return kvm_cpu_caps[x86_leaf] & __feature_bit(x86_feature);
> +}
> +
> +static __always_inline bool kvm_cpu_cap_has(unsigned x86_feature)
> +{
> +	return kvm_cpu_cap_get(x86_feature);
> +}

I know this works (and I even checked C99 to make sure that it works not
by accident) but I have to admit that explicit '!!' conversion to bool
always makes me feel safer :-)

> +
>  static __always_inline void kvm_cpu_cap_check_and_set(unsigned x86_feature)
>  {
>  	if (boot_cpu_has(x86_feature))
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c5ed199d6cd9..cb40737187a1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -912,7 +912,7 @@ static u64 kvm_host_cr4_reserved_bits(struct cpuinfo_x86 *c)
>  {
>  	u64 reserved_bits = __cr4_reserved_bits(cpu_has, c);
>  
> -	if (cpuid_ecx(0x7) & feature_bit(LA57))
> +	if (kvm_cpu_cap_has(X86_FEATURE_LA57))
>  		reserved_bits &= ~X86_CR4_LA57;
>  
>  	if (kvm_x86_ops->umip_emulated())

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Sean Christopherson Feb. 24, 2020, 11:23 p.m. UTC | #2
On Mon, Feb 24, 2020 at 11:08:30PM +0100, Vitaly Kuznetsov wrote:
> Sean Christopherson <sean.j.christopherson@intel.com> writes:
> 
> > Add accessor(s) for KVM cpu caps and use said accessor to detect
> > hardware support for LA57 instead of manually querying CPUID.
> >
> > No functional change intended.
> >
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > ---
> >  arch/x86/kvm/cpuid.h | 13 +++++++++++++
> >  arch/x86/kvm/x86.c   |  2 +-
> >  2 files changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> > index 7b71ae0ca05e..5ce4219d465f 100644
> > --- a/arch/x86/kvm/cpuid.h
> > +++ b/arch/x86/kvm/cpuid.h
> > @@ -274,6 +274,19 @@ static __always_inline void kvm_cpu_cap_set(unsigned x86_feature)
> >  	kvm_cpu_caps[x86_leaf] |= __feature_bit(x86_feature);
> >  }
> >  
> > +static __always_inline u32 kvm_cpu_cap_get(unsigned x86_feature)
> > +{
> > +	unsigned x86_leaf = x86_feature / 32;
> > +
> > +	reverse_cpuid_check(x86_leaf);
> > +	return kvm_cpu_caps[x86_leaf] & __feature_bit(x86_feature);
> > +}
> > +
> > +static __always_inline bool kvm_cpu_cap_has(unsigned x86_feature)
> > +{
> > +	return kvm_cpu_cap_get(x86_feature);
> > +}
> 
> I know this works (and I even checked C99 to make sure that it works not
> by accident) but I have to admit that explicit '!!' conversion to bool
> always makes me feel safer :-)

Eh, the flip side of blasting it everywhere is that people then forget why
the pattern exists in the first place and don't understand when it's truly
necessary.

> > +
> >  static __always_inline void kvm_cpu_cap_check_and_set(unsigned x86_feature)
> >  {
> >  	if (boot_cpu_has(x86_feature))
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index c5ed199d6cd9..cb40737187a1 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -912,7 +912,7 @@ static u64 kvm_host_cr4_reserved_bits(struct cpuinfo_x86 *c)
> >  {
> >  	u64 reserved_bits = __cr4_reserved_bits(cpu_has, c);
> >  
> > -	if (cpuid_ecx(0x7) & feature_bit(LA57))
> > +	if (kvm_cpu_cap_has(X86_FEATURE_LA57))
> >  		reserved_bits &= ~X86_CR4_LA57;
> >  
> >  	if (kvm_x86_ops->umip_emulated())
> 
> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> 
> -- 
> Vitaly
>
Paolo Bonzini Feb. 25, 2020, 3:12 p.m. UTC | #3
On 24/02/20 23:08, Vitaly Kuznetsov wrote:
>> +
>> +static __always_inline bool kvm_cpu_cap_has(unsigned x86_feature)
>> +{
>> +	return kvm_cpu_cap_get(x86_feature);
>> +}
> I know this works (and I even checked C99 to make sure that it works not
> by accident) but I have to admit that explicit '!!' conversion to bool
> always makes me feel safer :-)

Same here, I don't really like the automagic bool behavior...

Paolo
David Laight Feb. 25, 2020, 3:19 p.m. UTC | #4
From: Paolo Bonzini
> Sent: 25 February 2020 15:12
> On 24/02/20 23:08, Vitaly Kuznetsov wrote:
> >> +
> >> +static __always_inline bool kvm_cpu_cap_has(unsigned x86_feature)
> >> +{
> >> +	return kvm_cpu_cap_get(x86_feature);
> >> +}
> > I know this works (and I even checked C99 to make sure that it works not
> > by accident) but I have to admit that explicit '!!' conversion to bool
> > always makes me feel safer :-)
> 
> Same here, I don't really like the automagic bool behavior...

I just dislike 'bool'.

Conversion of 0/non-zero to 0/1 isn't completely free.
And something has to 'give' when the referenced memory location
doesn't contain 0 or 1.

One very old version of gcc made a complete hash of:
	bool_var |= function_returning_bool();

I'm not sure what the standard requires nor what current gcc
generates - but you want a 'logical or' instruction.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
Sean Christopherson Feb. 25, 2020, 9:22 p.m. UTC | #5
On Tue, Feb 25, 2020 at 04:12:28PM +0100, Paolo Bonzini wrote:
> On 24/02/20 23:08, Vitaly Kuznetsov wrote:
> >> +
> >> +static __always_inline bool kvm_cpu_cap_has(unsigned x86_feature)
> >> +{
> >> +	return kvm_cpu_cap_get(x86_feature);
> >> +}
> > I know this works (and I even checked C99 to make sure that it works not
> > by accident) but I have to admit that explicit '!!' conversion to bool
> > always makes me feel safer :-)
> 
> Same here, I don't really like the automagic bool behavior...

Sounds like I need to add '!!'?
Paolo Bonzini Feb. 26, 2020, 11:35 a.m. UTC | #6
On 25/02/20 22:22, Sean Christopherson wrote:
>>> I know this works (and I even checked C99 to make sure that it works not
>>> by accident) but I have to admit that explicit '!!' conversion to bool
>>> always makes me feel safer :-)
>> Same here, I don't really like the automagic bool behavior...
> Sounds like I need to add '!!'?
> 

Either that or "!= 0", as you prefer.

Paolo
diff mbox series

Patch

diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 7b71ae0ca05e..5ce4219d465f 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -274,6 +274,19 @@  static __always_inline void kvm_cpu_cap_set(unsigned x86_feature)
 	kvm_cpu_caps[x86_leaf] |= __feature_bit(x86_feature);
 }
 
+static __always_inline u32 kvm_cpu_cap_get(unsigned x86_feature)
+{
+	unsigned x86_leaf = x86_feature / 32;
+
+	reverse_cpuid_check(x86_leaf);
+	return kvm_cpu_caps[x86_leaf] & __feature_bit(x86_feature);
+}
+
+static __always_inline bool kvm_cpu_cap_has(unsigned x86_feature)
+{
+	return kvm_cpu_cap_get(x86_feature);
+}
+
 static __always_inline void kvm_cpu_cap_check_and_set(unsigned x86_feature)
 {
 	if (boot_cpu_has(x86_feature))
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c5ed199d6cd9..cb40737187a1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -912,7 +912,7 @@  static u64 kvm_host_cr4_reserved_bits(struct cpuinfo_x86 *c)
 {
 	u64 reserved_bits = __cr4_reserved_bits(cpu_has, c);
 
-	if (cpuid_ecx(0x7) & feature_bit(LA57))
+	if (kvm_cpu_cap_has(X86_FEATURE_LA57))
 		reserved_bits &= ~X86_CR4_LA57;
 
 	if (kvm_x86_ops->umip_emulated())