Commit 7ff6c035 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86: Remove stateful CPUID handling 



Remove the code for handling stateful CPUID 0x2 and mark the associated
flags as deprecated.  WARN if host CPUID 0x2.0.AL > 1, i.e. if by some
miracle a host with stateful CPUID 0x2 is encountered.

No known CPU exists that supports hardware accelerated virtualization
_and_ a stateful CPUID 0x2.  Barring an extremely contrived nested
virtualization scenario, stateful CPUID support is dead code.

Suggested-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Suggested-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent c571a144

Documentation/virt/kvm/api.rst

+4 −18
Original line number Diff line number Diff line
@@ -1574,8 +1574,8 @@ This ioctl would set vcpu's xcr to the value userspace specified. 
  };



  #define KVM_CPUID_FLAG_SIGNIFCANT_INDEX		BIT(0)

  #define KVM_CPUID_FLAG_STATEFUL_FUNC		BIT(1)

  #define KVM_CPUID_FLAG_STATE_READ_NEXT		BIT(2)

  #define KVM_CPUID_FLAG_STATEFUL_FUNC		BIT(1) /* deprecated */

  #define KVM_CPUID_FLAG_STATE_READ_NEXT		BIT(2) /* deprecated */



  struct kvm_cpuid_entry2 {

	__u32 function;
@@ -1626,13 +1626,6 @@ emulate them efficiently. The fields in each entry are defined as follows: 


        KVM_CPUID_FLAG_SIGNIFCANT_INDEX:

           if the index field is valid

        KVM_CPUID_FLAG_STATEFUL_FUNC:

           if cpuid for this function returns different values for successive

           invocations; there will be several entries with the same function,

           all with this flag set

        KVM_CPUID_FLAG_STATE_READ_NEXT:

           for KVM_CPUID_FLAG_STATEFUL_FUNC entries, set if this entry is

           the first entry to be read by a cpu



   eax, ebx, ecx, edx:

         the values returned by the cpuid instruction for
@@ -3347,8 +3340,8 @@ The member 'flags' is used for passing flags from userspace. 
::



  #define KVM_CPUID_FLAG_SIGNIFCANT_INDEX		BIT(0)

  #define KVM_CPUID_FLAG_STATEFUL_FUNC		BIT(1)

  #define KVM_CPUID_FLAG_STATE_READ_NEXT		BIT(2)

  #define KVM_CPUID_FLAG_STATEFUL_FUNC		BIT(1) /* deprecated */

  #define KVM_CPUID_FLAG_STATE_READ_NEXT		BIT(2) /* deprecated */



  struct kvm_cpuid_entry2 {

	__u32 function;
@@ -3394,13 +3387,6 @@ The fields in each entry are defined as follows: 


        KVM_CPUID_FLAG_SIGNIFCANT_INDEX:

           if the index field is valid

        KVM_CPUID_FLAG_STATEFUL_FUNC:

           if cpuid for this function returns different values for successive

           invocations; there will be several entries with the same function,

           all with this flag set

        KVM_CPUID_FLAG_STATE_READ_NEXT:

           for KVM_CPUID_FLAG_STATEFUL_FUNC entries, set if this entry is

           the first entry to be read by a cpu



   eax, ebx, ecx, edx:

arch/x86/kvm/cpuid.c

+13 −60
Original line number Diff line number Diff line
@@ -490,25 +490,16 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) 
		 * time, with the least-significant byte in EAX enumerating the

		 * number of times software should do CPUID(2, 0).

		 *

		 * Modern CPUs (quite likely every CPU KVM has *ever* run on)

		 * are less idiotic.  Intel's SDM states that EAX & 0xff "will

		 * always return 01H. Software should ignore this value and not

		 * Modern CPUs, i.e. every CPU KVM has *ever* run on are less

		 * idiotic.  Intel's SDM states that EAX & 0xff "will always

		 * return 01H. Software should ignore this value and not

		 * interpret it as an informational descriptor", while AMD's

		 * APM states that CPUID(2) is reserved.

		 *

		 * WARN if a frankenstein CPU that supports virtualization and

		 * a stateful CPUID.0x2 is encountered.

		 */

		max_idx = entry->eax & 0xff;

		if (likely(max_idx <= 1))

			break;



		entry->flags |= KVM_CPUID_FLAG_STATEFUL_FUNC;

		entry->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;



		for (i = 1; i < max_idx; ++i) {

			entry = do_host_cpuid(array, function, 0);

			if (!entry)

				goto out;

			entry->flags |= KVM_CPUID_FLAG_STATEFUL_FUNC;

		}

		WARN_ON_ONCE((entry->eax & 0xff) > 1);

		break;

	/* functions 4 and 0x8000001d have additional index. */

	case 4:
@@ -892,58 +883,20 @@ out_free: 
	return r;

}



static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i)

{

	struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i];

	struct kvm_cpuid_entry2 *ej;

	int j = i;

	int nent = vcpu->arch.cpuid_nent;



	e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT;

	/* when no next entry is found, the current entry[i] is reselected */

	do {

		j = (j + 1) % nent;

		ej = &vcpu->arch.cpuid_entries[j];

	} while (ej->function != e->function);



	ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;



	return j;

}



/* find an entry with matching function, matching index (if needed), and that

 * should be read next (if it's stateful) */

static int is_matching_cpuid_entry(struct kvm_cpuid_entry2 *e,

	u32 function, u32 index)

{

	if (e->function != function)

		return 0;

	if ((e->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX) && e->index != index)

		return 0;

	if (unlikely(e->flags & KVM_CPUID_FLAG_STATEFUL_FUNC) &&

	    !(e->flags & KVM_CPUID_FLAG_STATE_READ_NEXT))

		return 0;

	return 1;

}



struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,

					      u32 function, u32 index)

{

	struct kvm_cpuid_entry2 *e;

	int i;

	struct kvm_cpuid_entry2 *best = NULL;



	for (i = 0; i < vcpu->arch.cpuid_nent; ++i) {

		struct kvm_cpuid_entry2 *e;



		e = &vcpu->arch.cpuid_entries[i];

		if (is_matching_cpuid_entry(e, function, index)) {

			if (unlikely(e->flags & KVM_CPUID_FLAG_STATEFUL_FUNC))

				move_to_next_stateful_cpuid_entry(vcpu, i);

			best = e;

			break;

		}



		if (e->function == function && (e->index == index ||

		    !(e->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX)))

			return e;

	}

	return best;

	return NULL;

}

EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry);

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