Commit c24ed209 authored by Sean Christopherson's avatar Sean Christopherson
Browse files

KVM: SVM: Drop redundant check in AVIC code on ID during vCPU creation 



Drop avic_get_physical_id_entry()'s compatibility check on the incoming
ID, as its sole caller, avic_init_backing_page(), performs the exact same
check.  Drop avic_get_physical_id_entry() entirely as the only remaining
functionality is getting the address of the Physical ID table, and
accessing the array without an immediate bounds check is kludgy.

Opportunistically add a compile-time assertion to ensure the vcpu_id can't
result in a bounds overflow, e.g. if KVM (really) messed up a maximum
physical ID #define, as well as run-time assertions so that a NULL pointer
dereference is morphed into a safer WARN().

No functional change intended.

Tested-by: default avatarSairaj Kodilkar <sarunkod@amd.com>
Reviewed-by: default avatarNaveen N Rao (AMD) <naveen@kernel.org>
Link: https://lore.kernel.org/r/20250611224604.313496-15-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 1aa6e256

arch/x86/kvm/svm/avic.c

+15 −22
Original line number Diff line number Diff line
@@ -257,26 +257,12 @@ void avic_init_vmcb(struct vcpu_svm *svm, struct vmcb *vmcb) 
		avic_deactivate_vmcb(svm);

}



static u64 *avic_get_physical_id_entry(struct kvm_vcpu *vcpu,

				       unsigned int index)

{

	u64 *avic_physical_id_table;

	struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);



	if ((!x2avic_enabled && index > AVIC_MAX_PHYSICAL_ID) ||

	    (index > X2AVIC_MAX_PHYSICAL_ID))

		return NULL;



	avic_physical_id_table = page_address(kvm_svm->avic_physical_id_table_page);



	return &avic_physical_id_table[index];

}



static int avic_init_backing_page(struct kvm_vcpu *vcpu)

{

	u64 *entry, new_entry;

	int id = vcpu->vcpu_id;

	struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);

	struct vcpu_svm *svm = to_svm(vcpu);

	u32 id = vcpu->vcpu_id;

	u64 *table, new_entry;



	/*

	 * Inhibit AVIC if the vCPU ID is bigger than what is supported by AVIC
@@ -292,6 +278,9 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu) 
		return 0;

	}



	BUILD_BUG_ON((AVIC_MAX_PHYSICAL_ID + 1) * sizeof(*table) > PAGE_SIZE ||

		     (X2AVIC_MAX_PHYSICAL_ID + 1) * sizeof(*table) > PAGE_SIZE);



	if (WARN_ON_ONCE(!vcpu->arch.apic->regs))

		return -EINVAL;
@@ -310,9 +299,7 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu) 
	}



	/* Setting AVIC backing page address in the phy APIC ID table */

	entry = avic_get_physical_id_entry(vcpu, id);

	if (!entry)

		return -EINVAL;

	table = page_address(kvm_svm->avic_physical_id_table_page);



	/* Note, fls64() returns the bit position, +1. */

	BUILD_BUG_ON(__PHYSICAL_MASK_SHIFT >
@@ -320,9 +307,9 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu) 


	new_entry = avic_get_backing_page_address(svm) |

		    AVIC_PHYSICAL_ID_ENTRY_VALID_MASK;

	WRITE_ONCE(*entry, new_entry);

	WRITE_ONCE(table[id], new_entry);



	svm->avic_physical_id_cache = entry;

	svm->avic_physical_id_cache = &table[id];



	return 0;

}
@@ -1005,6 +992,9 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu) 
	if (WARN_ON(h_physical_id & ~AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK))

		return;



	if (WARN_ON_ONCE(!svm->avic_physical_id_cache))

		return;



	/*

	 * No need to update anything if the vCPU is blocking, i.e. if the vCPU

	 * is being scheduled in after being preempted.  The CPU entries in the
@@ -1045,6 +1035,9 @@ void avic_vcpu_put(struct kvm_vcpu *vcpu) 


	lockdep_assert_preemption_disabled();



	if (WARN_ON_ONCE(!svm->avic_physical_id_cache))

		return;



	/*

	 * Note, reading the Physical ID entry outside of ir_list_lock is safe

	 * as only the pCPU that has loaded (or is loading) the vCPU is allowed