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, 205 insertions, 0 deletions

diff --git a/drivers/macintosh/ans-lcd.c b/drivers/macintosh/ans-lcd.c
new file mode 100644
index 000000000..fa904b24a
--- /dev/null
+++ b/drivers/macintosh/ans-lcd.c
@@ -0,0 +1,205 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * /dev/lcd driver for Apple Network Servers.
+ */
+
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/miscdevice.h>
+#include <linux/fcntl.h>
+#include <linux/module.h>
+#include <linux/delay.h>
+#include <linux/fs.h>
+#include <linux/of.h>
+
+#include <linux/uaccess.h>
+#include <asm/sections.h>
+#include <asm/io.h>
+
+#include "ans-lcd.h"
+
+#define ANSLCD_ADDR		0xf301c000
+#define ANSLCD_CTRL_IX 0x00
+#define ANSLCD_DATA_IX 0x10
+
+static unsigned long anslcd_short_delay = 80;
+static unsigned long anslcd_long_delay = 3280;
+static volatile unsigned char __iomem *anslcd_ptr;
+static DEFINE_MUTEX(anslcd_mutex);
+
+#undef DEBUG
+
+static void
+anslcd_write_byte_ctrl ( unsigned char c )
+{
+#ifdef DEBUG
+	printk(KERN_DEBUG "LCD: CTRL byte: %02x\n",c);
+#endif
+	out_8(anslcd_ptr + ANSLCD_CTRL_IX, c);
+	switch(c) {
+		case 1:
+		case 2:
+		case 3:
+			udelay(anslcd_long_delay); break;
+		default: udelay(anslcd_short_delay);
+	}
+}
+
+static void
+anslcd_write_byte_data ( unsigned char c )
+{
+	out_8(anslcd_ptr + ANSLCD_DATA_IX, c);
+	udelay(anslcd_short_delay);
+}
+
+static ssize_t
+anslcd_write( struct file * file, const char __user * buf, 
+				size_t count, loff_t *ppos )
+{
+	const char __user *p = buf;
+	int i;
+
+#ifdef DEBUG
+	printk(KERN_DEBUG "LCD: write\n");
+#endif
+
+	if (!access_ok(buf, count))
+		return -EFAULT;
+
+	mutex_lock(&anslcd_mutex);
+	for ( i = *ppos; count > 0; ++i, ++p, --count ) 
+	{
+		char c;
+		__get_user(c, p);
+		anslcd_write_byte_data( c );
+	}
+	mutex_unlock(&anslcd_mutex);
+	*ppos = i;
+	return p - buf;
+}
+
+static long
+anslcd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	char ch, __user *temp;
+	long ret = 0;
+
+#ifdef DEBUG
+	printk(KERN_DEBUG "LCD: ioctl(%d,%d)\n",cmd,arg);
+#endif
+
+	mutex_lock(&anslcd_mutex);
+
+	switch ( cmd )
+	{
+	case ANSLCD_CLEAR:
+		anslcd_write_byte_ctrl ( 0x38 );
+		anslcd_write_byte_ctrl ( 0x0f );
+		anslcd_write_byte_ctrl ( 0x06 );
+		anslcd_write_byte_ctrl ( 0x01 );
+		anslcd_write_byte_ctrl ( 0x02 );
+		break;
+	case ANSLCD_SENDCTRL:
+		temp = (char __user *) arg;
+		__get_user(ch, temp);
+		for (; ch; temp++) { /* FIXME: This is ugly, but should work, as a \0 byte is not a valid command code */
+			anslcd_write_byte_ctrl ( ch );
+			__get_user(ch, temp);
+		}
+		break;
+	case ANSLCD_SETSHORTDELAY:
+		if (!capable(CAP_SYS_ADMIN))
+			ret =-EACCES;
+		else
+			anslcd_short_delay=arg;
+		break;
+	case ANSLCD_SETLONGDELAY:
+		if (!capable(CAP_SYS_ADMIN))
+			ret = -EACCES;
+		else
+			anslcd_long_delay=arg;
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	mutex_unlock(&anslcd_mutex);
+	return ret;
+}
+
+static int
+anslcd_open( struct inode * inode, struct file * file )
+{
+	return 0;
+}
+
+const struct file_operations anslcd_fops = {
+	.write		= anslcd_write,
+	.unlocked_ioctl	= anslcd_ioctl,
+	.open		= anslcd_open,
+	.llseek		= default_llseek,
+};
+
+static struct miscdevice anslcd_dev = {
+	LCD_MINOR,
+	"anslcd",
+	&anslcd_fops
+};
+
+static const char anslcd_logo[] __initconst =
+				"********************"  /* Line #1 */
+				"*      LINUX!      *"  /* Line #3 */
+				"*    Welcome to    *"  /* Line #2 */
+				"********************"; /* Line #4 */
+
+static int __init
+anslcd_init(void)
+{
+	int a;
+	int retval;
+	struct device_node* node;
+
+	node = of_find_node_by_name(NULL, "lcd");
+	if (!node || !of_node_name_eq(node->parent, "gc")) {
+		of_node_put(node);
+		return -ENODEV;
+	}
+	of_node_put(node);
+
+	anslcd_ptr = ioremap(ANSLCD_ADDR, 0x20);
+	
+	retval = misc_register(&anslcd_dev);
+	if(retval < 0){
+		printk(KERN_INFO "LCD: misc_register failed\n");
+		iounmap(anslcd_ptr);
+		return retval;
+	}
+
+#ifdef DEBUG
+	printk(KERN_DEBUG "LCD: init\n");
+#endif
+
+	mutex_lock(&anslcd_mutex);
+	anslcd_write_byte_ctrl ( 0x38 );
+	anslcd_write_byte_ctrl ( 0x0c );
+	anslcd_write_byte_ctrl ( 0x06 );
+	anslcd_write_byte_ctrl ( 0x01 );
+	anslcd_write_byte_ctrl ( 0x02 );
+	for(a=0;a<80;a++) {
+		anslcd_write_byte_data(anslcd_logo[a]);
+	}
+	mutex_unlock(&anslcd_mutex);
+	return 0;
+}
+
+static void __exit
+anslcd_exit(void)
+{
+	misc_deregister(&anslcd_dev);
+	iounmap(anslcd_ptr);
+}
+
+module_init(anslcd_init);
+module_exit(anslcd_exit);
+MODULE_LICENSE("GPL v2");