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>

2 files changed, 81 insertions, 0 deletions

diff --git a/arch/m68k/tools/amiga/Makefile b/arch/m68k/tools/amiga/Makefile
new file mode 100644
index 000000000..e6425b367
--- /dev/null
+++ b/arch/m68k/tools/amiga/Makefile
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CC =		m68k-cbm-amigados-gcc
+CFLAGS =	-Wall -O2
+
+
+All:		dmesg
+
+
+dmesg:		dmesg.c
+		$(CC) $(CFLAGS) -o dmesg dmesg.c -noixemul
+
diff --git a/arch/m68k/tools/amiga/dmesg.c b/arch/m68k/tools/amiga/dmesg.c
new file mode 100644
index 000000000..f8005a7ef
--- /dev/null
+++ b/arch/m68k/tools/amiga/dmesg.c
@@ -0,0 +1,69 @@
+/*
+ *  linux/arch/m68k/tools/amiga/dmesg.c -- Retrieve the kernel messages stored
+ *					   in Chip RAM with the kernel command
+ *					   line option `debug=mem'.
+ *
+ *  © Copyright 1996 by Geert Uytterhoeven <geert@linux-m68k.org>
+ *
+ *
+ *  Usage:
+ *
+ *	dmesg
+ *	dmesg <CHIPMEM_END>
+ *
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+
+#define CHIPMEM_START	0x00000000
+#define CHIPMEM_END	0x00200000	/* overridden by argv[1] */
+
+#define SAVEKMSG_MAGIC1	0x53415645	/* 'SAVE' */
+#define SAVEKMSG_MAGIC2	0x4B4D5347	/* 'KMSG' */
+
+struct savekmsg {
+    u_long magic1;	/* SAVEKMSG_MAGIC1 */
+    u_long magic2;	/* SAVEKMSG_MAGIC2 */
+    u_long magicptr;	/* address of magic1 */
+    u_long size;
+    char data[];
+};
+
+
+int main(int argc, char *argv[])
+{
+    u_long start = CHIPMEM_START, end = CHIPMEM_END, p;
+    int found = 0;
+    struct savekmsg *m = NULL;
+
+    if (argc >= 2)
+	end = strtoul(argv[1], NULL, 0);
+    printf("Searching for SAVEKMSG magic...\n");
+    for (p = start; p <= end-sizeof(struct savekmsg); p += 4) {
+	m = (struct savekmsg *)p;
+	if ((m->magic1 == SAVEKMSG_MAGIC1) && (m->magic2 == SAVEKMSG_MAGIC2) &&
+	    (m->magicptr == p)) {
+	    found = 1;
+	    break;
+	}
+    }
+    if (!found)
+	printf("Not found\n");
+    else {
+	printf("Found %ld bytes at 0x%08lx\n", m->size, (u_long)&m->data);
+	puts(">>>>>>>>>>>>>>>>>>>>");
+	fflush(stdout);
+	write(1, &m->data, m->size);
+	fflush(stdout);
+	puts("<<<<<<<<<<<<<<<<<<<<");
+    }
+    return(0);
+}