[46/61] KVM: x86: Remove the unnecessary loop on CPUID 0x7 sub-leafs
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Message ID 20200201185218.24473-47-sean.j.christopherson@intel.com
State New
Headers show
Series
  • KVM: x86: Introduce KVM cpu caps
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Commit Message

Sean Christopherson Feb. 1, 2020, 6:52 p.m. UTC
Explicitly handle CPUID 0x7 sub-leaf 1.  The kernel is currently aware
of exactly one feature in CPUID 0x7.1,  which means there is room for
another 127 features before CPUID 0x7.2 will see the light of day, i.e.
the looping is likely to be dead code for years to come.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/cpuid.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

Comments

Vitaly Kuznetsov Feb. 24, 2020, 10:25 p.m. UTC | #1
Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Explicitly handle CPUID 0x7 sub-leaf 1.  The kernel is currently aware
> of exactly one feature in CPUID 0x7.1,  which means there is room for
> another 127 features before CPUID 0x7.2 will see the light of day, i.e.
> the looping is likely to be dead code for years to come.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kvm/cpuid.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 7362e5238799..47f61f4497fb 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -533,11 +533,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		if (boot_cpu_has(X86_FEATURE_AMD_SSBD))
>  			cpuid_entry_set(entry, X86_FEATURE_SPEC_CTRL_SSBD);
>  
> -		for (i = 1, max_idx = entry->eax; i <= max_idx; i++) {
> -			if (WARN_ON_ONCE(i > 1))
> -				break;
> -
> -			entry = do_host_cpuid(array, function, i);
> +		/* KVM only supports 0x7.0 and 0x7.1, capped above via min(). */
> +		if (entry->eax == 1) {
> +			entry = do_host_cpuid(array, function, 1);
>  			if (!entry)
>  				goto out;

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

Patch
diff mbox series

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 7362e5238799..47f61f4497fb 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -533,11 +533,9 @@  static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		if (boot_cpu_has(X86_FEATURE_AMD_SSBD))
 			cpuid_entry_set(entry, X86_FEATURE_SPEC_CTRL_SSBD);
 
-		for (i = 1, max_idx = entry->eax; i <= max_idx; i++) {
-			if (WARN_ON_ONCE(i > 1))
-				break;
-
-			entry = do_host_cpuid(array, function, i);
+		/* KVM only supports 0x7.0 and 0x7.1, capped above via min(). */
+		if (entry->eax == 1) {
+			entry = do_host_cpuid(array, function, 1);
 			if (!entry)
 				goto out;