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Date:   Mon, 19 Dec 2022 16:35:34 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     torvalds@linux-foundation.org
Cc:     corbet@lwn.net, will@kernel.org, peterz@infradead.org,
        boqun.feng@gmail.com, mark.rutland@arm.com,
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Subject: [RFC][PATCH 09/12] x86,amd_iommu: Replace cmpxchg_double()
References: <20221219153525.632521981@infradead.org>
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Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 drivers/iommu/amd/amd_iommu_types.h |    9 +++++++--
 drivers/iommu/amd/iommu.c           |   10 ++++------
 2 files changed, 11 insertions(+), 8 deletions(-)

--- a/drivers/iommu/amd/amd_iommu_types.h
+++ b/drivers/iommu/amd/amd_iommu_types.h
@@ -979,8 +979,13 @@ union irte_ga_hi {
 };
 
 struct irte_ga {
-	union irte_ga_lo lo;
-	union irte_ga_hi hi;
+	union {
+		struct {
+			union irte_ga_lo lo;
+			union irte_ga_hi hi;
+		};
+		u128 irte;
+	};
 };
 
 struct irq_2_irte {
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -2992,10 +2992,10 @@ static int alloc_irq_index(struct amd_io
 static int modify_irte_ga(struct amd_iommu *iommu, u16 devid, int index,
 			  struct irte_ga *irte, struct amd_ir_data *data)
 {
-	bool ret;
 	struct irq_remap_table *table;
-	unsigned long flags;
 	struct irte_ga *entry;
+	unsigned long flags;
+	u128 old;
 
 	table = get_irq_table(iommu, devid);
 	if (!table)
@@ -3006,16 +3006,14 @@ static int modify_irte_ga(struct amd_iom
 	entry = (struct irte_ga *)table->table;
 	entry = &entry[index];
 
-	ret = cmpxchg_double(&entry->lo.val, &entry->hi.val,
-			     entry->lo.val, entry->hi.val,
-			     irte->lo.val, irte->hi.val);
 	/*
 	 * We use cmpxchg16 to atomically update the 128-bit IRTE,
 	 * and it cannot be updated by the hardware or other processors
 	 * behind us, so the return value of cmpxchg16 should be the
 	 * same as the old value.
 	 */
-	WARN_ON(!ret);
+	old = entry->irte;
+	WARN_ON(!try_cmpxchg128(&entry->irte, &old, irte->irte));
 
 	if (data)
 		data->ref = entry;