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, 126 insertions, 0 deletions

diff --git a/drivers/char/nsc_gpio.c b/drivers/char/nsc_gpio.c
new file mode 100644
index 000000000..2c9b12b85
--- /dev/null
+++ b/drivers/char/nsc_gpio.c
@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* linux/drivers/char/nsc_gpio.c
+
+   National Semiconductor common GPIO device-file/VFS methods.
+   Allows a user space process to control the GPIO pins.
+
+   Copyright (c) 2001,2002 Christer Weinigel <wingel@nano-system.com>
+   Copyright (c) 2005      Jim Cromie <jim.cromie@gmail.com>
+*/
+
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/nsc_gpio.h>
+#include <linux/platform_device.h>
+#include <linux/uaccess.h>
+#include <asm/io.h>
+
+#define NAME "nsc_gpio"
+
+void nsc_gpio_dump(struct nsc_gpio_ops *amp, unsigned index)
+{
+	/* retrieve current config w/o changing it */
+	u32 config = amp->gpio_config(index, ~0, 0);
+
+	/* user requested via 'v' command, so its INFO */
+	dev_info(amp->dev, "io%02u: 0x%04x %s %s %s %s %s %s %s\tio:%d/%d\n",
+		 index, config,
+		 (config & 1) ? "OE" : "TS",      /* output-enabled/tristate */
+		 (config & 2) ? "PP" : "OD",      /* push pull / open drain */
+		 (config & 4) ? "PUE" : "PUD",    /* pull up enabled/disabled */
+		 (config & 8) ? "LOCKED" : "",    /* locked / unlocked */
+		 (config & 16) ? "LEVEL" : "EDGE",/* level/edge input */
+		 (config & 32) ? "HI" : "LO",     /* trigger on rise/fall edge */
+		 (config & 64) ? "DEBOUNCE" : "", /* debounce */
+
+		 amp->gpio_get(index), amp->gpio_current(index));
+}
+
+ssize_t nsc_gpio_write(struct file *file, const char __user *data,
+		       size_t len, loff_t *ppos)
+{
+	unsigned m = iminor(file_inode(file));
+	struct nsc_gpio_ops *amp = file->private_data;
+	struct device *dev = amp->dev;
+	size_t i;
+	int err = 0;
+
+	for (i = 0; i < len; ++i) {
+		char c;
+		if (get_user(c, data + i))
+			return -EFAULT;
+		switch (c) {
+		case '0':
+			amp->gpio_set(m, 0);
+			break;
+		case '1':
+			amp->gpio_set(m, 1);
+			break;
+		case 'O':
+			dev_dbg(dev, "GPIO%d output enabled\n", m);
+			amp->gpio_config(m, ~1, 1);
+			break;
+		case 'o':
+			dev_dbg(dev, "GPIO%d output disabled\n", m);
+			amp->gpio_config(m, ~1, 0);
+			break;
+		case 'T':
+			dev_dbg(dev, "GPIO%d output is push pull\n", m);
+			amp->gpio_config(m, ~2, 2);
+			break;
+		case 't':
+			dev_dbg(dev, "GPIO%d output is open drain\n", m);
+			amp->gpio_config(m, ~2, 0);
+			break;
+		case 'P':
+			dev_dbg(dev, "GPIO%d pull up enabled\n", m);
+			amp->gpio_config(m, ~4, 4);
+			break;
+		case 'p':
+			dev_dbg(dev, "GPIO%d pull up disabled\n", m);
+			amp->gpio_config(m, ~4, 0);
+			break;
+		case 'v':
+			/* View Current pin settings */
+			amp->gpio_dump(amp, m);
+			break;
+		case '\n':
+			/* end of settings string, do nothing */
+			break;
+		default:
+			dev_err(dev, "io%2d bad setting: chr<0x%2x>\n",
+				m, (int)c);
+			err++;
+		}
+	}
+	if (err)
+		return -EINVAL;	/* full string handled, report error */
+
+	return len;
+}
+
+ssize_t nsc_gpio_read(struct file *file, char __user * buf,
+		      size_t len, loff_t * ppos)
+{
+	unsigned m = iminor(file_inode(file));
+	int value;
+	struct nsc_gpio_ops *amp = file->private_data;
+
+	value = amp->gpio_get(m);
+	if (put_user(value ? '1' : '0', buf))
+		return -EFAULT;
+
+	return 1;
+}
+
+/* common file-ops routines for both scx200_gpio and pc87360_gpio */
+EXPORT_SYMBOL(nsc_gpio_write);
+EXPORT_SYMBOL(nsc_gpio_read);
+EXPORT_SYMBOL(nsc_gpio_dump);
+
+MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>");
+MODULE_DESCRIPTION("NatSemi GPIO Common Methods");
+MODULE_LICENSE("GPL");