Commit 760849b1 authored by Paul Durrant's avatar Paul Durrant Committed by Paolo Bonzini
Browse files

KVM: x86: Make sure KVM_CPUID_FEATURES really are KVM_CPUID_FEATURES 



Currently when kvm_update_cpuid_runtime() runs, it assumes that the
KVM_CPUID_FEATURES leaf is located at 0x40000001. This is not true,
however, if Hyper-V support is enabled. In this case the KVM leaves will
be offset.

This patch introdues as new 'kvm_cpuid_base' field into struct
kvm_vcpu_arch to track the location of the KVM leaves and function
kvm_update_kvm_cpuid_base() (called from kvm_set_cpuid()) to locate the
leaves using the 'KVMKVMKVM\0\0\0' signature (which is now given a
definition in kvm_para.h). Adjustment of KVM_CPUID_FEATURES will hence now
target the correct leaf.

NOTE: A new for_each_possible_hypervisor_cpuid_base() macro is intoduced
      into processor.h to avoid having duplicate code for the iteration
      over possible hypervisor base leaves.

Signed-off-by: default avatarPaul Durrant <pdurrant@amazon.com>
Message-Id: <20211105095101.5384-3-pdurrant@amazon.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 8b44b174

arch/x86/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -725,6 +725,7 @@ struct kvm_vcpu_arch { 


	int cpuid_nent;

	struct kvm_cpuid_entry2 *cpuid_entries;

	u32 kvm_cpuid_base;



	u64 reserved_gpa_bits;

	int maxphyaddr;

arch/x86/include/asm/processor.h

+4 −1
Original line number Diff line number Diff line
@@ -807,11 +807,14 @@ static inline u32 amd_get_nodes_per_socket(void) { return 0; } 
static inline u32 amd_get_highest_perf(void)		{ return 0; }

#endif



#define for_each_possible_hypervisor_cpuid_base(function) \

	for (function = 0x40000000; function < 0x40010000; function += 0x100)



static inline uint32_t hypervisor_cpuid_base(const char *sig, uint32_t leaves)

{

	uint32_t base, eax, signature[3];



	for (base = 0x40000000; base < 0x40010000; base += 0x100) {

	for_each_possible_hypervisor_cpuid_base(base) {

		cpuid(base, &eax, &signature[0], &signature[1], &signature[2]);



		if (!memcmp(sig, signature, 12) &&

arch/x86/include/uapi/asm/kvm_para.h

+1 −0
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 
 * should be used to determine that a VM is running under KVM.

 */

#define KVM_CPUID_SIGNATURE	0x40000000

#define KVM_SIGNATURE "KVMKVMKVM\0\0\0"



/* This CPUID returns two feature bitmaps in eax, edx. Before enabling

 * a particular paravirtualization, the appropriate feature bit should

arch/x86/kernel/kvm.c

+1 −1
Original line number Diff line number Diff line
@@ -755,7 +755,7 @@ static noinline uint32_t __kvm_cpuid_base(void) 
		return 0;	/* So we don't blow up on old processors */



	if (boot_cpu_has(X86_FEATURE_HYPERVISOR))

		return hypervisor_cpuid_base("KVMKVMKVM\0\0\0", 0);

		return hypervisor_cpuid_base(KVM_SIGNATURE, 0);



	return 0;

}

arch/x86/kvm/cpuid.c

+40 −6
Original line number Diff line number Diff line
@@ -99,11 +99,45 @@ static int kvm_check_cpuid(struct kvm_cpuid_entry2 *entries, int nent) 
	return 0;

}



void kvm_update_pv_runtime(struct kvm_vcpu *vcpu)

static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu)

{

	struct kvm_cpuid_entry2 *best;

	u32 function;

	struct kvm_cpuid_entry2 *entry;



	vcpu->arch.kvm_cpuid_base = 0;



	for_each_possible_hypervisor_cpuid_base(function) {

		entry = kvm_find_cpuid_entry(vcpu, function, 0);



		if (entry) {

			u32 signature[3];



			signature[0] = entry->ebx;

			signature[1] = entry->ecx;

			signature[2] = entry->edx;



			BUILD_BUG_ON(sizeof(signature) > sizeof(KVM_SIGNATURE));

			if (!memcmp(signature, KVM_SIGNATURE, sizeof(signature))) {

				vcpu->arch.kvm_cpuid_base = function;

				break;

			}

		}

	}

}



	best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);

struct kvm_cpuid_entry2 *kvm_find_kvm_cpuid_features(struct kvm_vcpu *vcpu)

{

	u32 base = vcpu->arch.kvm_cpuid_base;



	if (!base)

		return NULL;



	return kvm_find_cpuid_entry(vcpu, base | KVM_CPUID_FEATURES, 0);

}



void kvm_update_pv_runtime(struct kvm_vcpu *vcpu)

{

	struct kvm_cpuid_entry2 *best = kvm_find_kvm_cpuid_features(vcpu);



	/*

	 * save the feature bitmap to avoid cpuid lookup for every PV
@@ -142,7 +176,7 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu) 
		     cpuid_entry_has(best, X86_FEATURE_XSAVEC)))

		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);



	best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);

	best = kvm_find_kvm_cpuid_features(vcpu);

	if (kvm_hlt_in_guest(vcpu->kvm) && best &&

		(best->eax & (1 << KVM_FEATURE_PV_UNHALT)))

		best->eax &= ~(1 << KVM_FEATURE_PV_UNHALT);
@@ -252,6 +286,7 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2, 
    vcpu->arch.cpuid_entries = e2;

    vcpu->arch.cpuid_nent = nent;



    kvm_update_kvm_cpuid_base(vcpu);

    kvm_update_cpuid_runtime(vcpu);

    kvm_vcpu_after_set_cpuid(vcpu);
@@ -872,8 +907,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) 
		}

		break;

	case KVM_CPUID_SIGNATURE: {

		static const char signature[12] = "KVMKVMKVM\0\0";

		const u32 *sigptr = (const u32 *)signature;

		const u32 *sigptr = (const u32 *)KVM_SIGNATURE;

		entry->eax = KVM_CPUID_FEATURES;

		entry->ebx = sigptr[0];

		entry->ecx = sigptr[1];