linux-kernel - [PATCH v6 05/29] x86/apic/vector: Do not allocate vectors for NMIs

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Date:   Thu,  5 May 2022 16:59:44 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Cc:     Tony Luck <tony.luck@...el.com>, Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Nicholas Piggin <npiggin@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        iommu@...ts.linux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: [PATCH v6 05/29] x86/apic/vector: Do not allocate vectors for NMIs

Vectors are meaningless when allocating IRQs with NMI as the delivery mode.
In such case, skip the reservation of IRQ vectors. Do it in the lowest-
level functions where the actual IRQ reservation takes place.

Since NMIs target specific CPUs, keep the functionality to find the best
CPU.

Cc: Andi Kleen <ak@...ux.intel.com>
Cc: "Ravi V. Shankar" <ravi.v.shankar@...el.com>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: iommu@...ts.linux-foundation.org
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: x86@...nel.org
Reviewed-by: Tony Luck <tony.luck@...el.com>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
Changes since v5:
 * Introduced this patch.

Changes since v4:
 * N/A

Changes since v3:
 * N/A

Changes since v2:
 * N/A

Changes since v1:
 * N/A
---
 arch/x86/kernel/apic/vector.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
index 838e220e8860..11f881f45cec 100644
--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -245,11 +245,20 @@ assign_vector_locked(struct irq_data *irqd, const struct cpumask *dest)
 	if (apicd->move_in_progress || !hlist_unhashed(&apicd->clist))
 		return -EBUSY;
 
+	if (apicd->hw_irq_cfg.delivery_mode == APIC_DELIVERY_MODE_NMI) {
+		cpu = irq_matrix_find_best_cpu(vector_matrix, dest);
+		apicd->cpu = cpu;
+		vector = 0;
+		goto no_vector;
+	}
+
 	vector = irq_matrix_alloc(vector_matrix, dest, resvd, &cpu);
 	trace_vector_alloc(irqd->irq, vector, resvd, vector);
 	if (vector < 0)
 		return vector;
 	apic_update_vector(irqd, vector, cpu);
+
+no_vector:
 	apic_update_irq_cfg(irqd, vector, cpu);
 
 	return 0;
@@ -321,12 +330,22 @@ assign_managed_vector(struct irq_data *irqd, const struct cpumask *dest)
 	/* set_affinity might call here for nothing */
 	if (apicd->vector && cpumask_test_cpu(apicd->cpu, vector_searchmask))
 		return 0;
+
+	if (apicd->hw_irq_cfg.delivery_mode == APIC_DELIVERY_MODE_NMI) {
+		cpu = irq_matrix_find_best_cpu_managed(vector_matrix, dest);
+		apicd->cpu = cpu;
+		vector = 0;
+		goto no_vector;
+	}
+
 	vector = irq_matrix_alloc_managed(vector_matrix, vector_searchmask,
 					  &cpu);
 	trace_vector_alloc_managed(irqd->irq, vector, vector);
 	if (vector < 0)
 		return vector;
 	apic_update_vector(irqd, vector, cpu);
+
+no_vector:
 	apic_update_irq_cfg(irqd, vector, cpu);
 	return 0;
 }
@@ -376,6 +395,10 @@ static void x86_vector_deactivate(struct irq_domain *dom, struct irq_data *irqd)
 	if (apicd->has_reserved)
 		return;
 
+	/* NMI IRQs do not have associated vectors; nothing to do. */
+	if (apicd->hw_irq_cfg.delivery_mode == APIC_DELIVERY_MODE_NMI)
+		return;
+
 	raw_spin_lock_irqsave(&vector_lock, flags);
 	clear_irq_vector(irqd);
 	if (apicd->can_reserve)
@@ -472,6 +495,10 @@ static void vector_free_reserved_and_managed(struct irq_data *irqd)
 	trace_vector_teardown(irqd->irq, apicd->is_managed,
 			      apicd->has_reserved);
 
+	/* NMI IRQs do not have associated vectors; nothing to do. */
+	if (apicd->hw_irq_cfg.delivery_mode == APIC_DELIVERY_MODE_NMI)
+		return;
+
 	if (apicd->has_reserved)
 		irq_matrix_remove_reserved(vector_matrix);
 	if (apicd->is_managed)
-- 
2.17.1