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SubjectRe: [PATCH] KVM: VMX: check match table
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On 01/10/2017 01:22, Nick Desaulniers wrote:
> On Wed, Sep 27, 2017 at 02:36:03PM +0200, Paolo Bonzini wrote:
>> On 26/09/2017 19:12, Josh Triplett wrote:
>>> Does this make any other checks redundant and removable?
>>
>> It would make sense to place it in cpu_has_kvm_support instead
>
> cpu_has_kvm_support() or cpu_has_vmx()?
>
>> , and the same in svm.c's has_svm.
>
> I don't follow (but I also don't know what any of these three letter
> acryonyms acronyms stand for), does svm depend on vmx or vice-versa?

Neither, one is Intel (VMX), the other is AMD (SVM).

Would this work for you? And again, is this only with clang?

---------- 8< ------------
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: [PATCH] KVM: clean up virtext.h

virtext.h does a lot of complicated checks where it could just use
boot_cpu_has instead. Remove all the cruft and stop using it in KVM
even, because KVM can just use x86_match_cpu.

As a side effect, this fixes

arch/x86/kvm/vmx.c:64:32: warning: variable vmx_cpu_id is not needed
and will not be emitted [-Wunneeded-internal-declaration]

Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/virtext.h b/arch/x86/include/asm/virtext.h
index 0116b2ee9e64..c7f7d5008d75 100644
--- a/arch/x86/include/asm/virtext.h
+++ b/arch/x86/include/asm/virtext.h
@@ -25,13 +25,6 @@
* VMX functions:
*/

-static inline int cpu_has_vmx(void)
-{
- unsigned long ecx = cpuid_ecx(1);
- return test_bit(5, &ecx); /* CPUID.1:ECX.VMX[bit 5] -> VT */
-}
-
-
/** Disable VMX on the current CPU
*
* vmxoff causes a undefined-opcode exception if vmxon was not run
@@ -49,22 +42,13 @@ static inline int cpu_vmx_enabled(void)
return __read_cr4() & X86_CR4_VMXE;
}

-/** Disable VMX if it is enabled on the current CPU
- *
- * You shouldn't call this if cpu_has_vmx() returns 0.
- */
-static inline void __cpu_emergency_vmxoff(void)
-{
- if (cpu_vmx_enabled())
- cpu_vmxoff();
-}
-
/** Disable VMX if it is supported and enabled on the current CPU
*/
static inline void cpu_emergency_vmxoff(void)
{
- if (cpu_has_vmx())
- __cpu_emergency_vmxoff();
+ if (boot_cpu_has(X86_FEATURE_VMX) &&
+ cpu_vmx_enabled())
+ cpu_vmxoff();
}


@@ -74,36 +58,6 @@ static inline void cpu_emergency_vmxoff(void)
* SVM functions:
*/

-/** Check if the CPU has SVM support
- *
- * You can use the 'msg' arg to get a message describing the problem,
- * if the function returns zero. Simply pass NULL if you are not interested
- * on the messages; gcc should take care of not generating code for
- * the messages on this case.
- */
-static inline int cpu_has_svm(const char **msg)
-{
- if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD) {
- if (msg)
- *msg = "not amd";
- return 0;
- }
-
- if (boot_cpu_data.extended_cpuid_level < SVM_CPUID_FUNC) {
- if (msg)
- *msg = "can't execute cpuid_8000000a";
- return 0;
- }
-
- if (!boot_cpu_has(X86_FEATURE_SVM)) {
- if (msg)
- *msg = "svm not available";
- return 0;
- }
- return 1;
-}
-
-
/** Disable SVM on the current CPU
*
* You should call this only if cpu_has_svm() returned true.
@@ -117,11 +71,17 @@ static inline void cpu_svm_disable(void)
wrmsrl(MSR_EFER, efer & ~EFER_SVME);
}

+static inline int cpu_svm_enabled(void)
+{
+ return rdmsrl(MSR_EFER) & EFER_SVME;
+}
+
/** Makes sure SVM is disabled, if it is supported on the CPU
*/
static inline void cpu_emergency_svm_disable(void)
{
- if (cpu_has_svm(NULL))
+ if (boot_cpu_has(X86_FEATURE_SVM) &&
+ cpu_svm_enabled())
cpu_svm_disable();
}

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 0e68f0b3cbf7..4ad26be59327 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -736,14 +736,7 @@ static void svm_init_osvw(struct kvm_vcpu *vcpu)

static int has_svm(void)
{
- const char *msg;
-
- if (!cpu_has_svm(&msg)) {
- printk(KERN_INFO "has_svm: %s\n", msg);
- return 0;
- }
-
- return 1;
+ return x86_match_cpu(svm_cpu_id);
}

static void svm_hardware_disable(void)
@@ -769,10 +762,6 @@ static int svm_hardware_enable(void)
if (efer & EFER_SVME)
return -EBUSY;

- if (!has_svm()) {
- pr_err("%s: err EOPNOTSUPP on %d\n", __func__, me);
- return -EINVAL;
- }
sd = per_cpu(svm_data, me);
if (!sd) {
pr_err("%s: svm_data is NULL on %d\n", __func__, me);
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index a2b804e10c95..9f6bcd9dd3c6 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3468,7 +3468,7 @@ static void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)

static __init int cpu_has_kvm_support(void)
{
- return cpu_has_vmx();
+ return x86_match_cpu(vmx_cpu_id);
}

static __init int vmx_disabled_by_bios(void)
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