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, 175 insertions, 0 deletions

diff --git a/drivers/video/fbdev/maxinefb.c b/drivers/video/fbdev/maxinefb.c
new file mode 100644
index 000000000..67d4bd881
--- /dev/null
+++ b/drivers/video/fbdev/maxinefb.c
@@ -0,0 +1,175 @@
+/*
+ *      linux/drivers/video/maxinefb.c
+ *
+ *	DECstation 5000/xx onboard framebuffer support ... derived from:
+ *	"HP300 Topcat framebuffer support (derived from macfb of all things)
+ *	Phil Blundell <philb@gnu.org> 1998", the original code can be
+ *      found in the file hpfb.c in the same directory.
+ *
+ *      DECstation related code Copyright (C) 1999,2000,2001 by
+ *      Michael Engel <engel@unix-ag.org> and
+ *      Karsten Merker <merker@linuxtag.org>.
+ *      This file is subject to the terms and conditions of the GNU General
+ *      Public License.  See the file COPYING in the main directory of this
+ *      archive for more details.
+ *
+ */
+
+/*
+ * Changes:
+ * 2001/01/27 removed debugging and testing code, fixed fb_ops
+ *            initialization which had caused a crash before,
+ *            general cleanup, first official release (KM)
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/fb.h>
+#include <video/maxinefb.h>
+
+/* bootinfo.h defines the machine type values, needed when checking */
+/* whether are really running on a maxine, KM                       */
+#include <asm/bootinfo.h>
+
+static struct fb_info fb_info;
+
+static const struct fb_var_screeninfo maxinefb_defined = {
+	.xres =		1024,
+	.yres =		768,
+	.xres_virtual =	1024,
+	.yres_virtual =	768,
+	.bits_per_pixel =8,
+	.activate =	FB_ACTIVATE_NOW,
+	.height =	-1,
+	.width =	-1,
+	.vmode =	FB_VMODE_NONINTERLACED,
+};
+
+static struct fb_fix_screeninfo maxinefb_fix __initdata = {
+	.id =		"Maxine",
+	.smem_len =	(1024*768),
+	.type =		FB_TYPE_PACKED_PIXELS,
+	.visual =	FB_VISUAL_PSEUDOCOLOR,
+	.line_length =	1024,
+};
+
+/* Handle the funny Inmos RamDAC/video controller ... */
+
+static void maxinefb_ims332_write_register(int regno, register unsigned int val)
+{
+	register unsigned char *regs = (char *) MAXINEFB_IMS332_ADDRESS;
+	unsigned char *wptr;
+
+	wptr = regs + 0xa0000 + (regno << 4);
+	*((volatile unsigned int *) (regs)) = (val >> 8) & 0xff00;
+	*((volatile unsigned short *) (wptr)) = val;
+}
+
+#if 0
+/* dead code: leave here for hardware interface documentation */
+static unsigned int maxinefb_ims332_read_register(int regno)
+{
+	register unsigned char *regs = (char *) MAXINEFB_IMS332_ADDRESS;
+	unsigned char *rptr;
+	register unsigned int j, k;
+
+	rptr = regs + 0x80000 + (regno << 4);
+	j = *((volatile unsigned short *) rptr);
+	k = *((volatile unsigned short *) regs);
+
+	return (j & 0xffff) | ((k & 0xff00) << 8);
+}
+#endif
+
+/* Set the palette */
+static int maxinefb_setcolreg(unsigned regno, unsigned red, unsigned green,
+			      unsigned blue, unsigned transp, struct fb_info *info)
+{
+	/* value to be written into the palette reg. */
+	unsigned long hw_colorvalue = 0;
+
+	if (regno > 255)
+		return 1;
+
+	red   >>= 8;    /* The cmap fields are 16 bits    */
+	green >>= 8;    /* wide, but the harware colormap */
+	blue  >>= 8;    /* registers are only 8 bits wide */
+
+	hw_colorvalue = (blue << 16) + (green << 8) + (red);
+
+	maxinefb_ims332_write_register(IMS332_REG_COLOR_PALETTE + regno,
+				       hw_colorvalue);
+	return 0;
+}
+
+static const struct fb_ops maxinefb_ops = {
+	.owner		= THIS_MODULE,
+	FB_DEFAULT_IOMEM_OPS,
+	.fb_setcolreg	= maxinefb_setcolreg,
+};
+
+static int __init maxinefb_init(void)
+{
+	unsigned long fboff;
+	unsigned long fb_start;
+	int i;
+
+	if (fb_get_options("maxinefb", NULL))
+		return -ENODEV;
+
+	/* Validate we're on the proper machine type */
+	if (mips_machtype != MACH_DS5000_XX) {
+		return -EINVAL;
+	}
+
+	printk(KERN_INFO "Maxinefb: Personal DECstation detected\n");
+	printk(KERN_INFO "Maxinefb: initializing onboard framebuffer\n");
+
+	/* Framebuffer display memory base address */
+	fb_start = DS5000_xx_ONBOARD_FBMEM_START;
+
+	/* Clear screen */
+	for (fboff = fb_start; fboff < fb_start + 0x1ffff; fboff++)
+		*(volatile unsigned char *)fboff = 0x0;
+
+	maxinefb_fix.smem_start = fb_start;
+
+	/* erase hardware cursor */
+	for (i = 0; i < 512; i++) {
+		maxinefb_ims332_write_register(IMS332_REG_CURSOR_RAM + i,
+					       0);
+		/*
+		   if (i&0x8 == 0)
+		   maxinefb_ims332_write_register (IMS332_REG_CURSOR_RAM + i, 0x0f);
+		   else
+		   maxinefb_ims332_write_register (IMS332_REG_CURSOR_RAM + i, 0xf0);
+		 */
+	}
+
+	fb_info.fbops = &maxinefb_ops;
+	fb_info.screen_base = (char *)maxinefb_fix.smem_start;
+	fb_info.var = maxinefb_defined;
+	fb_info.fix = maxinefb_fix;
+
+	fb_alloc_cmap(&fb_info.cmap, 256, 0);
+
+	if (register_framebuffer(&fb_info) < 0)
+		return -ENODEV;
+	return 0;
+}
+
+static void __exit maxinefb_exit(void)
+{
+	unregister_framebuffer(&fb_info);
+}
+
+module_init(maxinefb_init);
+module_exit(maxinefb_exit);
+
+MODULE_LICENSE("GPL");