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, 232 insertions, 0 deletions

diff --git a/drivers/mtd/tests/stresstest.c b/drivers/mtd/tests/stresstest.c
new file mode 100644
index 000000000..944f960a4
--- /dev/null
+++ b/drivers/mtd/tests/stresstest.c
@@ -0,0 +1,232 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2006-2008 Nokia Corporation
+ *
+ * Test random reads, writes and erases on MTD device.
+ *
+ * Author: Adrian Hunter <ext-adrian.hunter@nokia.com>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/err.h>
+#include <linux/mtd/mtd.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/vmalloc.h>
+#include <linux/random.h>
+
+#include "mtd_test.h"
+
+static int dev = -EINVAL;
+module_param(dev, int, S_IRUGO);
+MODULE_PARM_DESC(dev, "MTD device number to use");
+
+static int count = 10000;
+module_param(count, int, S_IRUGO);
+MODULE_PARM_DESC(count, "Number of operations to do (default is 10000)");
+
+static struct mtd_info *mtd;
+static unsigned char *writebuf;
+static unsigned char *readbuf;
+static unsigned char *bbt;
+static int *offsets;
+
+static int pgsize;
+static int bufsize;
+static int ebcnt;
+static int pgcnt;
+
+static int rand_eb(void)
+{
+	unsigned int eb;
+
+again:
+	/* Read or write up 2 eraseblocks at a time - hence 'ebcnt - 1' */
+	eb = get_random_u32_below(ebcnt - 1);
+	if (bbt[eb])
+		goto again;
+	return eb;
+}
+
+static int rand_offs(void)
+{
+	return get_random_u32_below(bufsize);
+}
+
+static int rand_len(int offs)
+{
+	return get_random_u32_below(bufsize - offs);
+}
+
+static int do_read(void)
+{
+	int eb = rand_eb();
+	int offs = rand_offs();
+	int len = rand_len(offs);
+	loff_t addr;
+
+	if (bbt[eb + 1]) {
+		if (offs >= mtd->erasesize)
+			offs -= mtd->erasesize;
+		if (offs + len > mtd->erasesize)
+			len = mtd->erasesize - offs;
+	}
+	addr = (loff_t)eb * mtd->erasesize + offs;
+	return mtdtest_read(mtd, addr, len, readbuf);
+}
+
+static int do_write(void)
+{
+	int eb = rand_eb(), offs, err, len;
+	loff_t addr;
+
+	offs = offsets[eb];
+	if (offs >= mtd->erasesize) {
+		err = mtdtest_erase_eraseblock(mtd, eb);
+		if (err)
+			return err;
+		offs = offsets[eb] = 0;
+	}
+	len = rand_len(offs);
+	len = ((len + pgsize - 1) / pgsize) * pgsize;
+	if (offs + len > mtd->erasesize) {
+		if (bbt[eb + 1])
+			len = mtd->erasesize - offs;
+		else {
+			err = mtdtest_erase_eraseblock(mtd, eb + 1);
+			if (err)
+				return err;
+			offsets[eb + 1] = 0;
+		}
+	}
+	addr = (loff_t)eb * mtd->erasesize + offs;
+	err = mtdtest_write(mtd, addr, len, writebuf);
+	if (unlikely(err))
+		return err;
+	offs += len;
+	while (offs > mtd->erasesize) {
+		offsets[eb++] = mtd->erasesize;
+		offs -= mtd->erasesize;
+	}
+	offsets[eb] = offs;
+	return 0;
+}
+
+static int do_operation(void)
+{
+	if (get_random_u32_below(2))
+		return do_read();
+	else
+		return do_write();
+}
+
+static int __init mtd_stresstest_init(void)
+{
+	int err;
+	int i, op;
+	uint64_t tmp;
+
+	printk(KERN_INFO "\n");
+	printk(KERN_INFO "=================================================\n");
+
+	if (dev < 0) {
+		pr_info("Please specify a valid mtd-device via module parameter\n");
+		pr_crit("CAREFUL: This test wipes all data on the specified MTD device!\n");
+		return -EINVAL;
+	}
+
+	pr_info("MTD device: %d\n", dev);
+
+	mtd = get_mtd_device(NULL, dev);
+	if (IS_ERR(mtd)) {
+		err = PTR_ERR(mtd);
+		pr_err("error: cannot get MTD device\n");
+		return err;
+	}
+
+	if (mtd->writesize == 1) {
+		pr_info("not NAND flash, assume page size is 512 "
+		       "bytes.\n");
+		pgsize = 512;
+	} else
+		pgsize = mtd->writesize;
+
+	tmp = mtd->size;
+	do_div(tmp, mtd->erasesize);
+	ebcnt = tmp;
+	pgcnt = mtd->erasesize / pgsize;
+
+	pr_info("MTD device size %llu, eraseblock size %u, "
+	       "page size %u, count of eraseblocks %u, pages per "
+	       "eraseblock %u, OOB size %u\n",
+	       (unsigned long long)mtd->size, mtd->erasesize,
+	       pgsize, ebcnt, pgcnt, mtd->oobsize);
+
+	if (ebcnt < 2) {
+		pr_err("error: need at least 2 eraseblocks\n");
+		err = -ENOSPC;
+		goto out_put_mtd;
+	}
+
+	/* Read or write up 2 eraseblocks at a time */
+	bufsize = mtd->erasesize * 2;
+
+	err = -ENOMEM;
+	readbuf = vmalloc(bufsize);
+	writebuf = vmalloc(bufsize);
+	offsets = kmalloc_objs(int, ebcnt);
+	if (!readbuf || !writebuf || !offsets)
+		goto out;
+	for (i = 0; i < ebcnt; i++)
+		offsets[i] = mtd->erasesize;
+	get_random_bytes(writebuf, bufsize);
+
+	bbt = kzalloc(ebcnt, GFP_KERNEL);
+	if (!bbt)
+		goto out;
+	err = mtdtest_scan_for_bad_eraseblocks(mtd, bbt, 0, ebcnt);
+	if (err)
+		goto out;
+
+	/* Do operations */
+	pr_info("doing operations\n");
+	for (op = 0; op < count; op++) {
+		if ((op & 1023) == 0)
+			pr_info("%d operations done\n", op);
+		err = do_operation();
+		if (err)
+			goto out;
+
+		err = mtdtest_relax();
+		if (err)
+			goto out;
+	}
+	pr_info("finished, %d operations done\n", op);
+
+out:
+	kfree(offsets);
+	kfree(bbt);
+	vfree(writebuf);
+	vfree(readbuf);
+out_put_mtd:
+	put_mtd_device(mtd);
+	if (err)
+		pr_info("error %d occurred\n", err);
+	printk(KERN_INFO "=================================================\n");
+	return err;
+}
+module_init(mtd_stresstest_init);
+
+static void __exit mtd_stresstest_exit(void)
+{
+	return;
+}
+module_exit(mtd_stresstest_exit);
+
+MODULE_DESCRIPTION("Stress test module");
+MODULE_AUTHOR("Adrian Hunter");
+MODULE_LICENSE("GPL");