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, 80 insertions, 0 deletions

diff --git a/arch/powerpc/boot/hack-coff.c b/arch/powerpc/boot/hack-coff.c
new file mode 100644
index 000000000..6bf0c9430
--- /dev/null
+++ b/arch/powerpc/boot/hack-coff.c
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * hack-coff.c - hack the header of an xcoff file to fill in
+ * a few fields needed by the Open Firmware xcoff loader on
+ * Power Macs but not initialized by objcopy.
+ *
+ * Copyright (C) Paul Mackerras 1997.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#include "rs6000.h"
+
+#define AOUT_MAGIC	0x010b
+
+#define get_16be(x)	((((unsigned char *)(x))[0] << 8) \
+			 + ((unsigned char *)(x))[1])
+#define put_16be(x, v)	(((unsigned char *)(x))[0] = (v) >> 8, \
+			 ((unsigned char *)(x))[1] = (v) & 0xff)
+#define get_32be(x)	((((unsigned char *)(x))[0] << 24) \
+			 + (((unsigned char *)(x))[1] << 16) \
+			 + (((unsigned char *)(x))[2] << 8) \
+			 + ((unsigned char *)(x))[3])
+
+int
+main(int ac, char **av)
+{
+    int fd;
+    int i, nsect;
+    int aoutsz;
+    struct external_filehdr fhdr;
+    struct aouthdr aout;
+    struct external_scnhdr shdr;
+
+    if (ac != 2) {
+	fprintf(stderr, "Usage: hack-coff coff-file\n");
+	exit(1);
+    }
+    if ((fd = open(av[1], 2)) == -1) {
+	perror(av[2]);
+	exit(1);
+    }
+    if (read(fd, &fhdr, sizeof(fhdr)) != sizeof(fhdr))
+	goto readerr;
+    i = get_16be(fhdr.f_magic);
+    if (i != U802TOCMAGIC && i != U802WRMAGIC && i != U802ROMAGIC) {
+	fprintf(stderr, "%s: not an xcoff file\n", av[1]);
+	exit(1);
+    }
+    aoutsz = get_16be(fhdr.f_opthdr);
+    if (read(fd, &aout, aoutsz) != aoutsz)
+	goto readerr;
+    nsect = get_16be(fhdr.f_nscns);
+    for (i = 0; i < nsect; ++i) {
+	if (read(fd, &shdr, sizeof(shdr)) != sizeof(shdr))
+	    goto readerr;
+	if (strcmp(shdr.s_name, ".text") == 0) {
+	    put_16be(aout.o_snentry, i+1);
+	    put_16be(aout.o_sntext, i+1);
+	} else if (strcmp(shdr.s_name, ".data") == 0) {
+	    put_16be(aout.o_sndata, i+1);
+	} else if (strcmp(shdr.s_name, ".bss") == 0) {
+	    put_16be(aout.o_snbss, i+1);
+	}
+    }
+    put_16be(aout.magic, AOUT_MAGIC);
+    if (lseek(fd, (long) sizeof(struct external_filehdr), 0) == -1
+	|| write(fd, &aout, aoutsz) != aoutsz) {
+	fprintf(stderr, "%s: write error\n", av[1]);
+	exit(1);
+    }
+    close(fd);
+    exit(0);
+
+readerr:
+    fprintf(stderr, "%s: read error or file too short\n", av[1]);
+    exit(1);
+}