Re: [PATCH v2 1/5] KVM: x86: Add return value to kvm_cpuid().

[Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>]

On 8/17/2017 8:29 PM, Paolo Bonzini wrote:
> On 17/08/2017 21:52, Yu Zhang wrote:
> > diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> > index ac15193..3e759cf 100644
> > --- a/arch/x86/kvm/cpuid.h
> > +++ b/arch/x86/kvm/cpuid.h
> > @@ -21,7 +21,14 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
> >   int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
> >   			      struct kvm_cpuid2 *cpuid,
> >   			      struct kvm_cpuid_entry2 __user *entries);
> > -void kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx);
> > +
> > +enum {
> > +	NO_CHECK_LIMIT = 0,
> > +	CHECK_LIMIT = 1,
> > +};
> emulate.c should not include cpuid.h.  The argument can be simply a
> bool, though.

Thanks, Paolo.
So we just use true/false in emulate.c & svm.c, is this OK?
BTW could you please

> > +bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
> > +	       u32 *ecx, u32 *edx, int check_limit);
> >   
> >   int cpuid_query_maxphyaddr(struct kvm_vcpu *vcpu);
> >   
> > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> > index fb00559..46daa37 100644
> > --- a/arch/x86/kvm/emulate.c
> > +++ b/arch/x86/kvm/emulate.c
> > @@ -28,6 +28,7 @@
> >   
> >   #include "x86.h"
> >   #include "tss.h"
> > +#include "cpuid.h"
> >   
> >   /*
> >    * Operand types
> > @@ -2333,8 +2334,10 @@ static int emulator_has_longmode(struct x86_emulate_ctxt *ctxt)
> >   
> >   	eax = 0x80000001;
> >   	ecx = 0;
> > -	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
> > -	return edx & bit(X86_FEATURE_LM);
> > +	if (ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, NO_CHECK_LIMIT))
> > +		return edx & bit(X86_FEATURE_LM);
> > +	else
> > +		return 0;
> >   }
> >   
> >   #define GET_SMSTATE(type, smbase, offset)				  \
> > @@ -2636,7 +2639,7 @@ static bool vendor_intel(struct x86_emulate_ctxt *ctxt)
> >   	u32 eax, ebx, ecx, edx;
> >   
> >   	eax = ecx = 0;
> > -	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
> > +	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, NO_CHECK_LIMIT);
> >   	return ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx
> >   		&& ecx == X86EMUL_CPUID_VENDOR_GenuineIntel_ecx
> >   		&& edx == X86EMUL_CPUID_VENDOR_GenuineIntel_edx;
> > @@ -2656,7 +2659,7 @@ static bool em_syscall_is_enabled(struct x86_emulate_ctxt *ctxt)
> >   
> >   	eax = 0x00000000;
> >   	ecx = 0x00000000;
> > -	ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
> > +	ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, NO_CHECK_LIMIT);
> >   	/*
> >   	 * Intel ("GenuineIntel")
> >   	 * remark: Intel CPUs only support "syscall" in 64bit
> > @@ -3551,7 +3554,7 @@ static int em_movbe(struct x86_emulate_ctxt *ctxt)
> >   	/*
> >   	 * Check MOVBE is set in the guest-visible CPUID leaf.
> >   	 */
> > -	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
> > +	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, CHECK_LIMIT);
> This should be NO_CHECK_LIMIT.
>
> Otherwise okay!

Then I guess check_fxsr() should also use NO_CHECK_LIMIT('false' for a 
bool argument),
because it's also for eax=1?

And what about svm_vcpu_reset()?

I am not sure if leaf 1 is always available. And if the answer is yes, I 
do not think any of these
3 places(em_movbe/check_fxsr/svm_vcpu_reset) will need to fall back to 
check_cpuid_limit(),
nor do we need to check the return value of get_cpuid(). Do you agree? :-)

Yu

> Paolo
>
> >   	if (!(ecx & FFL(MOVBE)))
> >   		return emulate_ud(ctxt);
> >   
> > @@ -3865,7 +3868,7 @@ static int em_cpuid(struct x86_emulate_ctxt *ctxt)
> >   
> >   	eax = reg_read(ctxt, VCPU_REGS_RAX);
> >   	ecx = reg_read(ctxt, VCPU_REGS_RCX);
> > -	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
> > +	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, CHECK_LIMIT);
> >   	*reg_write(ctxt, VCPU_REGS_RAX) = eax;
> >   	*reg_write(ctxt, VCPU_REGS_RBX) = ebx;
> >   	*reg_write(ctxt, VCPU_REGS_RCX) = ecx;
> > @@ -3924,7 +3927,7 @@ static int check_fxsr(struct x86_emulate_ctxt *ctxt)
> >   {
> >   	u32 eax = 1, ebx, ecx = 0, edx;
> >   
> > -	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
> > +	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, CHECK_LIMIT);
> >   	if (!(edx & FFL(FXSR)))
> >   		return emulate_ud(ctxt);
> >   
> > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > index 1fa9ee5..9def4a8 100644
> > --- a/arch/x86/kvm/svm.c
> > +++ b/arch/x86/kvm/svm.c
> > @@ -1580,7 +1580,7 @@ static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> >   	}
> >   	init_vmcb(svm);
> >   
> > -	kvm_cpuid(vcpu, &eax, &dummy, &dummy, &dummy);
> > +	kvm_cpuid(vcpu, &eax, &dummy, &dummy, &dummy, CHECK_LIMIT);
> >   	kvm_register_write(vcpu, VCPU_REGS_RDX, eax);
> >   
> >   	if (kvm_vcpu_apicv_active(vcpu) && !init_event)
> > diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> > index 0a6cc67..8a202c4 100644
> > --- a/arch/x86/kvm/trace.h
> > +++ b/arch/x86/kvm/trace.h
> > @@ -151,8 +151,8 @@ TRACE_EVENT(kvm_fast_mmio,
> >    */
> >   TRACE_EVENT(kvm_cpuid,
> >   	TP_PROTO(unsigned int function, unsigned long rax, unsigned long rbx,
> > -		 unsigned long rcx, unsigned long rdx),
> > -	TP_ARGS(function, rax, rbx, rcx, rdx),
> > +		 unsigned long rcx, unsigned long rdx, bool found),
> > +	TP_ARGS(function, rax, rbx, rcx, rdx, found),
> >   
> >   	TP_STRUCT__entry(
> >   		__field(	unsigned int,	function	)
> > @@ -160,6 +160,7 @@ TRACE_EVENT(kvm_cpuid,
> >   		__field(	unsigned long,	rbx		)
> >   		__field(	unsigned long,	rcx		)
> >   		__field(	unsigned long,	rdx		)
> > +		__field(	bool,		found		)
> >   	),
> >   
> >   	TP_fast_assign(
> > @@ -168,11 +169,13 @@ TRACE_EVENT(kvm_cpuid,
> >   		__entry->rbx		= rbx;
> >   		__entry->rcx		= rcx;
> >   		__entry->rdx		= rdx;
> > +		__entry->found		= found;
> >   	),
> >   
> > -	TP_printk("func %x rax %lx rbx %lx rcx %lx rdx %lx",
> > +	TP_printk("func %x rax %lx rbx %lx rcx %lx rdx %lx, cpuid entry %s",
> >   		  __entry->function, __entry->rax,
> > -		  __entry->rbx, __entry->rcx, __entry->rdx)
> > +		  __entry->rbx, __entry->rcx, __entry->rdx,
> > +		  __entry->found ? "found" : "not found")
> >   );
> >   
> >   #define AREG(x) { APIC_##x, "APIC_" #x }
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index e40a779..ee99fc1 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -5213,10 +5213,10 @@ static int emulator_intercept(struct x86_emulate_ctxt *ctxt,
> >   	return kvm_x86_ops->check_intercept(emul_to_vcpu(ctxt), info, stage);
> >   }
> >   
> > -static void emulator_get_cpuid(struct x86_emulate_ctxt *ctxt,
> > -			       u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
> > +static bool emulator_get_cpuid(struct x86_emulate_ctxt *ctxt,
> > +			u32 *eax, u32 *ebx, u32 *ecx, u32 *edx, int check_limit)
> >   {
> > -	kvm_cpuid(emul_to_vcpu(ctxt), eax, ebx, ecx, edx);
> > +	return kvm_cpuid(emul_to_vcpu(ctxt), eax, ebx, ecx, edx, check_limit);
> >   }
> >   
> >   static ulong emulator_read_gpr(struct x86_emulate_ctxt *ctxt, unsigned reg)