KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 151 insertions, 0 deletions

diff --git a/drivers/video/fbdev/q40fb.c b/drivers/video/fbdev/q40fb.c
new file mode 100644
index 000000000..1ff8fa176
--- /dev/null
+++ b/drivers/video/fbdev/q40fb.c
@@ -0,0 +1,151 @@
+/*
+ * linux/drivers/video/q40fb.c -- Q40 frame buffer device
+ *
+ * Copyright (C) 2001
+ *
+ *      Richard Zidlicky <rz@linux-m68k.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.
+ */
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/platform_device.h>
+
+#include <linux/uaccess.h>
+#include <asm/setup.h>
+#include <asm/q40_master.h>
+#include <linux/fb.h>
+#include <linux/module.h>
+
+#define Q40_PHYS_SCREEN_ADDR 0xFE800000
+
+static struct fb_fix_screeninfo q40fb_fix = {
+	.id		= "Q40",
+	.smem_len	= 1024*1024,
+	.type		= FB_TYPE_PACKED_PIXELS,
+	.visual		= FB_VISUAL_TRUECOLOR,
+	.line_length	= 1024*2,
+	.accel		= FB_ACCEL_NONE,
+};
+
+static const struct fb_var_screeninfo q40fb_var = {
+	.xres		= 1024,
+	.yres		= 512,
+	.xres_virtual	= 1024,
+	.yres_virtual	= 512,
+	.bits_per_pixel	= 16,
+    	.red		= {6, 5, 0},
+	.green		= {11, 5, 0},
+	.blue		= {0, 6, 0},
+	.activate	= FB_ACTIVATE_NOW,
+	.height		= 230,
+	.width		= 300,
+	.vmode		= FB_VMODE_NONINTERLACED,
+};
+
+static int q40fb_setcolreg(unsigned regno, unsigned red, unsigned green,
+			   unsigned blue, unsigned transp,
+			   struct fb_info *info)
+{
+    /*
+     *  Set a single color register. The values supplied have a 16 bit
+     *  magnitude.
+     *  Return != 0 for invalid regno.
+     */
+
+    if (regno > 255)
+	    return 1;
+    red>>=11;
+    green>>=11;
+    blue>>=10;
+
+    if (regno < 16) {
+	((u32 *)info->pseudo_palette)[regno] = ((red & 31) <<6) |
+					       ((green & 31) << 11) |
+					       (blue & 63);
+    }
+    return 0;
+}
+
+static const struct fb_ops q40fb_ops = {
+	.owner		= THIS_MODULE,
+	FB_DEFAULT_IOMEM_OPS,
+	.fb_setcolreg	= q40fb_setcolreg,
+};
+
+static int q40fb_probe(struct platform_device *dev)
+{
+	struct fb_info *info;
+
+	if (!MACH_IS_Q40)
+		return -ENXIO;
+
+	/* mapped in q40/config.c */
+	q40fb_fix.smem_start = Q40_PHYS_SCREEN_ADDR;
+
+	info = framebuffer_alloc(sizeof(u32) * 16, &dev->dev);
+	if (!info)
+		return -ENOMEM;
+
+	info->var = q40fb_var;
+	info->fix = q40fb_fix;
+	info->fbops = &q40fb_ops;
+	info->pseudo_palette = info->par;
+	info->par = NULL;
+	info->screen_base = (char *) q40fb_fix.smem_start;
+
+	if (fb_alloc_cmap(&info->cmap, 256, 0) < 0) {
+		framebuffer_release(info);
+		return -ENOMEM;
+	}
+
+	master_outb(3, DISPLAY_CONTROL_REG);
+
+	if (register_framebuffer(info) < 0) {
+		printk(KERN_ERR "Unable to register Q40 frame buffer\n");
+		fb_dealloc_cmap(&info->cmap);
+		framebuffer_release(info);
+		return -EINVAL;
+	}
+
+	fb_info(info, "Q40 frame buffer alive and kicking !\n");
+	return 0;
+}
+
+static struct platform_driver q40fb_driver = {
+	.probe	= q40fb_probe,
+	.driver	= {
+		.name	= "q40fb",
+	},
+};
+
+static struct platform_device q40fb_device = {
+	.name	= "q40fb",
+};
+
+static int __init q40fb_init(void)
+{
+	int ret = 0;
+
+	if (fb_get_options("q40fb", NULL))
+		return -ENODEV;
+
+	ret = platform_driver_register(&q40fb_driver);
+
+	if (!ret) {
+		ret = platform_device_register(&q40fb_device);
+		if (ret)
+			platform_driver_unregister(&q40fb_driver);
+	}
+	return ret;
+}
+
+module_init(q40fb_init);
+MODULE_LICENSE("GPL");