[for-5.2 4/9] docs/system/virtio-pmem.rst: Fix minor style issues

[Peter Maydell]

The virtio-pmem documentation has some minor style issues we hadn't
noticed since we weren't rendering it in our docs:

 * Sphinx doesn't complain about overlong title-underlining the
   way it complains about too-short underlining, but it looks odd;
   make the underlines of the top level title the right length

 * Indent of paragraphs makes them render as blockquotes;
   remove the indent so they just render as normal text

 * Leading 'o' isn't rst markup, so it just renders as a literal
   "o"; reformat as a subsection heading instead

 * "QEMU" in the document title and section headings are a bit
   odd and unnecessary since this is the QEMU manual; delete
   or rephrase them

 * There's no need to specify what QEMU version the device first
   appeared in.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 docs/system/virtio-pmem.rst | 55 ++++++++++++++++++-------------------
 1 file changed, 27 insertions(+), 28 deletions(-)

diff --git a/docs/system/virtio-pmem.rst b/docs/system/virtio-pmem.rst
index 4bf5d004432..e5f91eff1c2 100644
--- a/docs/system/virtio-pmem.rst
+++ b/docs/system/virtio-pmem.rst
@@ -1,38 +1,37 @@
 
-========================
-QEMU virtio pmem
-========================
+===========
+virtio pmem
+===========
 
- This document explains the setup and usage of the virtio pmem device
- which is available since QEMU v4.1.0.
-
- The virtio pmem device is a paravirtualized persistent memory device
- on regular (i.e non-NVDIMM) storage.
+This document explains the setup and usage of the virtio pmem device.
+The virtio pmem device is a paravirtualized persistent memory device
+on regular (i.e non-NVDIMM) storage.
 
 Usecase
 --------
 
-  Virtio pmem allows to bypass the guest page cache and directly use
-  host page cache. This reduces guest memory footprint as the host can
-  make efficient memory reclaim decisions under memory pressure.
+Virtio pmem allows to bypass the guest page cache and directly use
+host page cache. This reduces guest memory footprint as the host can
+make efficient memory reclaim decisions under memory pressure.
 
-o How does virtio-pmem compare to the nvdimm emulation supported by QEMU?
+How does virtio-pmem compare to the nvdimm emulation?
+-----------------------------------------------------
 
-  NVDIMM emulation on regular (i.e. non-NVDIMM) host storage does not
-  persist the guest writes as there are no defined semantics in the device
-  specification. The virtio pmem device provides guest write persistence
-  on non-NVDIMM host storage.
+NVDIMM emulation on regular (i.e. non-NVDIMM) host storage does not
+persist the guest writes as there are no defined semantics in the device
+specification. The virtio pmem device provides guest write persistence
+on non-NVDIMM host storage.
 
 virtio pmem usage
 -----------------
 
-  A virtio pmem device backed by a memory-backend-file can be created on
-  the QEMU command line as in the following example::
+A virtio pmem device backed by a memory-backend-file can be created on
+the QEMU command line as in the following example::
 
     -object 
memory-backend-file,id=mem1,share,mem-path=./virtio_pmem.img,size=4G
     -device virtio-pmem-pci,memdev=mem1,id=nv1
 
-  where:
+where:
 
   - "object memory-backend-file,id=mem1,share,mem-path=<image>, size=<image 
size>"
     creates a backend file with the specified size.
@@ -40,8 +39,8 @@ virtio pmem usage
   - "device virtio-pmem-pci,id=nvdimm1,memdev=mem1" creates a virtio pmem
     pci device whose storage is provided by above memory backend device.
 
-  Multiple virtio pmem devices can be created if multiple pairs of "-object"
-  and "-device" are provided.
+Multiple virtio pmem devices can be created if multiple pairs of "-object"
+and "-device" are provided.
 
 Hotplug
 -------
@@ -59,14 +58,14 @@ the guest::
 Guest Data Persistence
 ----------------------
 
- Guest data persistence on non-NVDIMM requires guest userspace applications
- to perform fsync/msync. This is different from a real nvdimm backend where
- no additional fsync/msync is required. This is to persist guest writes in
- host backing file which otherwise remains in host page cache and there is
- risk of losing the data in case of power failure.
+Guest data persistence on non-NVDIMM requires guest userspace applications
+to perform fsync/msync. This is different from a real nvdimm backend where
+no additional fsync/msync is required. This is to persist guest writes in
+host backing file which otherwise remains in host page cache and there is
+risk of losing the data in case of power failure.
 
- With virtio pmem device, MAP_SYNC mmap flag is not supported. This provides
- a hint to application to perform fsync for write persistence.
+With virtio pmem device, MAP_SYNC mmap flag is not supported. This provides
+a hint to application to perform fsync for write persistence.
 
 Limitations
 ------------
-- 
2.20.1