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, 188 insertions, 0 deletions

diff --git a/arch/powerpc/xmon/nonstdio.c b/arch/powerpc/xmon/nonstdio.c
new file mode 100644
index 000000000..9b0d85bff
--- /dev/null
+++ b/arch/powerpc/xmon/nonstdio.c
@@ -0,0 +1,188 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 1996-2005 Paul Mackerras.
+ */
+#include <linux/string.h>
+#include <asm/udbg.h>
+#include <asm/time.h>
+#include "nonstdio.h"
+
+static bool paginating, paginate_skipping;
+static unsigned long paginate_lpp; /* Lines Per Page */
+static unsigned long paginate_pos;
+
+void xmon_start_pagination(void)
+{
+	paginating = true;
+	paginate_skipping = false;
+	paginate_pos = 0;
+}
+
+void xmon_end_pagination(void)
+{
+	paginating = false;
+}
+
+void xmon_set_pagination_lpp(unsigned long lpp)
+{
+	paginate_lpp = lpp;
+}
+
+static int xmon_readchar(void)
+{
+	if (udbg_getc)
+		return udbg_getc();
+	return -1;
+}
+
+static int xmon_write(const char *ptr, int nb)
+{
+	int rv = 0;
+	const char *p = ptr, *q;
+	const char msg[] = "[Hit a key (a:all, q:truncate, any:next page)]";
+
+	if (nb <= 0)
+		return rv;
+
+	if (paginating && paginate_skipping)
+		return nb;
+
+	if (paginate_lpp) {
+		while (paginating && (q = strchr(p, '\n'))) {
+			rv += udbg_write(p, q - p + 1);
+			p = q + 1;
+			paginate_pos++;
+
+			if (paginate_pos >= paginate_lpp) {
+				udbg_write(msg, strlen(msg));
+
+				switch (xmon_readchar()) {
+				case 'a':
+					paginating = false;
+					break;
+				case 'q':
+					paginate_skipping = true;
+					break;
+				default:
+					/* nothing */
+					break;
+				}
+
+				paginate_pos = 0;
+				udbg_write("\r\n", 2);
+
+				if (paginate_skipping)
+					return nb;
+			}
+		}
+	}
+
+	return rv + udbg_write(p, nb - (p - ptr));
+}
+
+int xmon_putchar(int c)
+{
+	char ch = c;
+
+	if (c == '\n')
+		xmon_putchar('\r');
+	return xmon_write(&ch, 1) == 1? c: -1;
+}
+
+static char line[256];
+static char *lineptr;
+static int lineleft;
+
+static int xmon_getchar(void)
+{
+	int c;
+
+	if (lineleft == 0) {
+		lineptr = line;
+		for (;;) {
+			c = xmon_readchar();
+			if (c == -1 || c == 4)
+				break;
+			if (c == '\r' || c == '\n') {
+				*lineptr++ = '\n';
+				xmon_putchar('\n');
+				break;
+			}
+			switch (c) {
+			case 0177:
+			case '\b':
+				if (lineptr > line) {
+					xmon_putchar('\b');
+					xmon_putchar(' ');
+					xmon_putchar('\b');
+					--lineptr;
+				}
+				break;
+			case 'U' & 0x1F:
+				while (lineptr > line) {
+					xmon_putchar('\b');
+					xmon_putchar(' ');
+					xmon_putchar('\b');
+					--lineptr;
+				}
+				break;
+			default:
+				if (lineptr >= &line[sizeof(line) - 1])
+					xmon_putchar('\a');
+				else {
+					xmon_putchar(c);
+					*lineptr++ = c;
+				}
+			}
+		}
+		lineleft = lineptr - line;
+		lineptr = line;
+	}
+	if (lineleft == 0)
+		return -1;
+	--lineleft;
+	return *lineptr++;
+}
+
+char *xmon_gets(char *str, int nb)
+{
+	char *p;
+	int c;
+
+	for (p = str; p < str + nb - 1; ) {
+		c = xmon_getchar();
+		if (c == -1) {
+			if (p == str)
+				return NULL;
+			break;
+		}
+		*p++ = c;
+		if (c == '\n')
+			break;
+	}
+	*p = 0;
+	return str;
+}
+
+void xmon_printf(const char *format, ...)
+{
+	va_list args;
+	static char xmon_outbuf[1024];
+	int rc, n;
+
+	va_start(args, format);
+	n = vsnprintf(xmon_outbuf, sizeof(xmon_outbuf), format, args);
+	va_end(args);
+
+	rc = xmon_write(xmon_outbuf, n);
+
+	if (n && rc == 0) {
+		/* No udbg hooks, fallback to printk() - dangerous */
+		pr_cont("%s", xmon_outbuf);
+	}
+}
+
+void xmon_puts(const char *str)
+{
+	xmon_write(str, strlen(str));
+}