6.1-stable review patch. If anyone has any objections, please let me know.
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From: Sean Christopherson seanjc@google.com
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@vger.kernel.org Tested-by: Alejandro Jimenez alejandro.j.jimenez@oracle.com Reviewed-by: Joao Martins joao.m.martins@oracle.com Link: https://lore.kernel.org/r/20230808233132.2499764-2-seanjc@google.com Signed-off-by: Sean Christopherson seanjc@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 @@ -1022,10 +1022,11 @@ 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;
@@ -1033,19 +1034,15 @@ 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) @@ -1053,6 +1050,7 @@ 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();
@@ -1069,6 +1067,8 @@ 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));
entry &= ~AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK; @@ -1077,25 +1077,40 @@ 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)