[Xen-devel] [PATCH v2 01/10] AMD/IOMMU: restrict feature logging

From: "Jan Beulich" <JBeulich@suse.com>
To: "xen-devel" <xen-devel@lists.xenproject.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Brian Woods <brian.woods@amd.com>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Subject: [Xen-devel] [PATCH v2 01/10] AMD/IOMMU: restrict feature logging
Date: Thu, 27 Jun 2019 09:19:06 -0600	[thread overview]
Message-ID: <5D14DE6A020000780023B97B@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <5D14DDA6020000780023B96E@prv1-mh.provo.novell.com>

The common case is all IOMMUs having the same features. Log them only
for the first IOMMU, or for any that have a differing feature set.

Requested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v2: New.

--- a/xen/drivers/passthrough/amd/iommu_detect.c
+++ b/xen/drivers/passthrough/amd/iommu_detect.c
@@ -62,6 +62,7 @@ void __init get_iommu_features(struct am
 {
     u32 low, high;
     int i = 0 ;
+    const struct amd_iommu *first;
     static const char *__initdata feature_str[] = {
         "- Prefetch Pages Command", 
         "- Peripheral Page Service Request", 
@@ -89,6 +90,11 @@ void __init get_iommu_features(struct am
 
     iommu->features = ((u64)high << 32) | low;
 
+    /* Don't log the same set of features over and over. */
+    first = list_first_entry(&amd_iommu_head, struct amd_iommu, list);
+    if ( iommu != first && iommu->features == first->features )
+        return;
+
     printk("AMD-Vi: IOMMU Extended Features:\n");
 
     while ( feature_str[i] )




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