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From: "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>
To: qemu-devel@nongnu.org, vkuznets@redhat.com, mst@redhat.com,
	jasowang@redhat.com, pbonzini@redhat.com
Subject: [PATCH v3 2/2] vhost: Only align sections for vhost-user
Date: Thu, 16 Jan 2020 20:24:14 +0000
Message-ID: <20200116202414.157959-3-dgilbert@redhat.com> (raw)
In-Reply-To: <20200116202414.157959-1-dgilbert@redhat.com>

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

I added hugepage alignment code in c1ece84e7c9 to deal with
vhost-user + postcopy which needs aligned pages when using userfault.
However, on x86 the lower 2MB of address space tends to be shotgun'd
with small fragments around the 512-640k range - e.g. video RAM, and
with HyperV synic pages tend to sit around there - again splitting
it up.  The alignment code complains with a 'Section rounded to ...'
error and gives up.

Since vhost-user already filters out devices without an fd
(see vhost-user.c vhost_user_mem_section_filter) it shouldn't be
affected by those overlaps.

Turn the alignment off on vhost-kernel so that it doesn't try
and align, and thus won't hit the rounding issues.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 hw/virtio/vhost.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 774d87d98e..25fd469179 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -547,26 +547,28 @@ static void vhost_region_add_section(struct vhost_dev *dev,
     uintptr_t mrs_host = (uintptr_t)memory_region_get_ram_ptr(section->mr) +
                          section->offset_within_region;
     RAMBlock *mrs_rb = section->mr->ram_block;
-    size_t mrs_page = qemu_ram_pagesize(mrs_rb);
 
     trace_vhost_region_add_section(section->mr->name, mrs_gpa, mrs_size,
                                    mrs_host);
 
-    /* Round the section to it's page size */
-    /* First align the start down to a page boundary */
-    uint64_t alignage = mrs_host & (mrs_page - 1);
-    if (alignage) {
-        mrs_host -= alignage;
-        mrs_size += alignage;
-        mrs_gpa  -= alignage;
-    }
-    /* Now align the size up to a page boundary */
-    alignage = mrs_size & (mrs_page - 1);
-    if (alignage) {
-        mrs_size += mrs_page - alignage;
-    }
-    trace_vhost_region_add_section_aligned(section->mr->name, mrs_gpa, mrs_size,
-                                           mrs_host);
+    if (dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER) {   
+        /* Round the section to it's page size */
+        /* First align the start down to a page boundary */
+        size_t mrs_page = qemu_ram_pagesize(mrs_rb);
+        uint64_t alignage = mrs_host & (mrs_page - 1);
+        if (alignage) {
+            mrs_host -= alignage;
+            mrs_size += alignage;
+            mrs_gpa  -= alignage;
+        }
+        /* Now align the size up to a page boundary */
+        alignage = mrs_size & (mrs_page - 1);
+        if (alignage) {
+            mrs_size += mrs_page - alignage;
+        }
+        trace_vhost_region_add_section_aligned(section->mr->name, mrs_gpa, mrs_size,
+                                               mrs_host);
+    }
 
     if (dev->n_tmp_sections) {
         /* Since we already have at least one section, lets see if
-- 
2.24.1



  parent reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16 20:24 [PATCH v3 0/2] Fix hyperv synic on vhost Dr. David Alan Gilbert (git)
2020-01-16 20:24 ` [PATCH v3 1/2] vhost: Add names to section rounded warning Dr. David Alan Gilbert (git)
2020-01-16 20:24 ` Dr. David Alan Gilbert (git) [this message]
2020-01-17 12:52   ` [PATCH v3 2/2] vhost: Only align sections for vhost-user Paolo Bonzini
2020-01-17 13:40     ` Michael S. Tsirkin
2020-01-17 13:58       ` Paolo Bonzini
2020-01-17 14:25         ` Michael S. Tsirkin
2020-01-17 15:06           ` Paolo Bonzini
2020-01-17 15:10         ` Dr. David Alan Gilbert
2020-01-17  0:24 ` [PATCH v3 0/2] Fix hyperv synic on vhost no-reply
2020-01-17 12:47   ` Dr. David Alan Gilbert

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