[PATCH v3 13/62] KVM: SVM: Drop redundant check in AVIC code on ID during vCPU creation
From: Sean Christopherson <seanjc@google.com>
Date: 2025-06-11 22:47:19
Also in:
kvm, kvmarm, linux-iommu, lkml
Subsystem:
kernel virtual machine for x86 (kvm/x86), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Sean Christopherson, Paolo Bonzini, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
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: Sairaj Kodilkar <redacted> Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/kvm/svm/avic.c | 37 +++++++++++++++---------------------- 1 file changed, 15 insertions(+), 22 deletions(-)
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index f0a74b102c57..948bab48083b 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c@@ -256,26 +256,12 @@ 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
@@ -291,6 +277,9 @@ 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;
@@ -309,9 +298,7 @@ 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 >
@@ -319,9 +306,9 @@ 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; }
@@ -1004,6 +991,9 @@ 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
@@ -1044,6 +1034,9 @@ 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
--
2.50.0.rc1.591.g9c95f17f64-goog