KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/Documentation/fb/pvr2fb.rst b/Documentation/fb/pvr2fb.rst
new file mode 100644
index 000000000..315ce085a
--- /dev/null
+++ b/Documentation/fb/pvr2fb.rst
@@ -0,0 +1,66 @@
+===============================================
+pvr2fb - PowerVR 2 graphics frame buffer driver
+===============================================
+
+This is a driver for PowerVR 2 based graphics frame buffers, such as the
+one found in the Dreamcast.
+
+Advantages:
+
+ * It provides a nice large console (128 cols + 48 lines with 1024x768)
+   without using tiny, unreadable fonts (NOT on the Dreamcast)
+ * You can run XF86_FBDev on top of /dev/fb0
+ * Most important: boot logo :-)
+
+Disadvantages:
+
+ * Driver is largely untested on non-Dreamcast systems.
+
+Configuration
+=============
+
+You can pass kernel command line options to pvr2fb with
+`video=pvr2fb:option1,option2:value2,option3` (multiple options should be
+separated by comma, values are separated from options by `:`).
+
+Accepted options:
+
+==========  ==================================================================
+font:X      default font to use. All fonts are supported, including the
+	    SUN12x22 font which is very nice at high resolutions.
+
+
+mode:X      default video mode with format [xres]x[yres]-<bpp>@<refresh rate>
+	    The following video modes are supported:
+	    640x640-16@60, 640x480-24@60, 640x480-32@60. The Dreamcast
+	    defaults to 640x480-16@60. At the time of writing the
+	    24bpp and 32bpp modes function poorly. Work to fix that is
+	    ongoing
+
+	    Note: the 640x240 mode is currently broken, and should not be
+	    used for any reason. It is only mentioned here as a reference.
+
+inverse     invert colors on screen (for LCD displays)
+
+nomtrr      disables write combining on frame buffer. This slows down driver
+	    but there is reported minor incompatibility between GUS DMA and
+	    XFree under high loads if write combining is enabled (sound
+	    dropouts). MTRR is enabled by default on systems that have it
+	    configured and that support it.
+
+cable:X     cable type. This can be any of the following: vga, rgb, and
+	    composite. If none is specified, we guess.
+
+output:X    output type. This can be any of the following: pal, ntsc, and
+	    vga. If none is specified, we guess.
+==========  ==================================================================
+
+X11
+===
+
+XF86_FBDev has been shown to work on the Dreamcast in the past - though not yet
+on any 2.6 series kernel.
+
+Paul Mundt <lethal@linuxdc.org>
+
+Updated by Adrian McMenamin <adrian@mcmen.demon.co.uk>