6.5-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sean Christopherson <seanjc@xxxxxxxxxx> commit 4c08e737f056fec930b416a2bd37ed266d724f95 upstream. Hoist the acquisition of ir_list_lock from avic_update_iommu_vcpu_affinity() to its two callers, avic_vcpu_load() and avic_vcpu_put(), specifically to encapsulate the write to the vCPU's entry in the AVIC Physical ID table. This will allow a future fix to pull information from the Physical ID entry when updating the IRTE, without potentially consuming stale information, i.e. without racing with the vCPU being (un)loaded. Add a comment to call out that ir_list_lock does NOT protect against multiple writers, specifically that reading the Physical ID entry in avic_vcpu_put() outside of the lock is safe. To preserve some semblance of independence from ir_list_lock, keep the READ_ONCE() in avic_vcpu_load() even though acuiring the spinlock effectively ensures the load(s) will be generated after acquiring the lock. Cc: stable@xxxxxxxxxxxxxxx Tested-by: Alejandro Jimenez <alejandro.j.jimenez@xxxxxxxxxx> Reviewed-by: Joao Martins <joao.m.martins@xxxxxxxxxx> Link: https://lore.kernel.org/r/20230808233132.2499764-2-seanjc@xxxxxxxxxx Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kvm/svm/avic.c | 31 +++++++++++++++++++++++-------- 1 file changed, 23 insertions(+), 8 deletions(-) --- a/arch/x86/kvm/svm/avic.c +++ b/arch/x86/kvm/svm/avic.c @@ -986,10 +986,11 @@ static inline int avic_update_iommu_vcpu_affinity(struct kvm_vcpu *vcpu, int cpu, bool r) { int ret = 0; - unsigned long flags; struct amd_svm_iommu_ir *ir; struct vcpu_svm *svm = to_svm(vcpu); + lockdep_assert_held(&svm->ir_list_lock); + if (!kvm_arch_has_assigned_device(vcpu->kvm)) return 0; @@ -997,19 +998,15 @@ avic_update_iommu_vcpu_affinity(struct k * Here, we go through the per-vcpu ir_list to update all existing * interrupt remapping table entry targeting this vcpu. */ - spin_lock_irqsave(&svm->ir_list_lock, flags); - if (list_empty(&svm->ir_list)) - goto out; + return 0; list_for_each_entry(ir, &svm->ir_list, node) { ret = amd_iommu_update_ga(cpu, r, ir->data); if (ret) - break; + return ret; } -out: - spin_unlock_irqrestore(&svm->ir_list_lock, flags); - return ret; + return 0; } void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu) @@ -1017,6 +1014,7 @@ void avic_vcpu_load(struct kvm_vcpu *vcp u64 entry; int h_physical_id = kvm_cpu_get_apicid(cpu); struct vcpu_svm *svm = to_svm(vcpu); + unsigned long flags; lockdep_assert_preemption_disabled(); @@ -1033,6 +1031,8 @@ void avic_vcpu_load(struct kvm_vcpu *vcp if (kvm_vcpu_is_blocking(vcpu)) return; + spin_lock_irqsave(&svm->ir_list_lock, flags); + entry = READ_ONCE(*(svm->avic_physical_id_cache)); WARN_ON_ONCE(entry & AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK); @@ -1042,25 +1042,40 @@ void avic_vcpu_load(struct kvm_vcpu *vcp WRITE_ONCE(*(svm->avic_physical_id_cache), entry); avic_update_iommu_vcpu_affinity(vcpu, h_physical_id, true); + + spin_unlock_irqrestore(&svm->ir_list_lock, flags); } void avic_vcpu_put(struct kvm_vcpu *vcpu) { u64 entry; struct vcpu_svm *svm = to_svm(vcpu); + unsigned long flags; lockdep_assert_preemption_disabled(); + /* + * 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 + * to modify the entry, and preemption is disabled. I.e. the vCPU + * can't be scheduled out and thus avic_vcpu_{put,load}() can't run + * recursively. + */ entry = READ_ONCE(*(svm->avic_physical_id_cache)); /* Nothing to do if IsRunning == '0' due to vCPU blocking. */ if (!(entry & AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK)) return; + spin_lock_irqsave(&svm->ir_list_lock, flags); + avic_update_iommu_vcpu_affinity(vcpu, -1, 0); entry &= ~AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK; WRITE_ONCE(*(svm->avic_physical_id_cache), entry); + + spin_unlock_irqrestore(&svm->ir_list_lock, flags); + } void avic_refresh_virtual_apic_mode(struct kvm_vcpu *vcpu)
