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, 142 insertions, 0 deletions

diff --git a/arch/m68k/lib/uaccess.c b/arch/m68k/lib/uaccess.c
new file mode 100644
index 000000000..7646e461a
--- /dev/null
+++ b/arch/m68k/lib/uaccess.c
@@ -0,0 +1,142 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/uaccess.h>
+
+unsigned long __generic_copy_from_user(void *to, const void __user *from,
+				       unsigned long n)
+{
+	unsigned long tmp, res;
+
+	asm volatile ("\n"
+		"	tst.l	%0\n"
+		"	jeq	2f\n"
+		"1:	"MOVES".l	(%1)+,%3\n"
+		"	move.l	%3,(%2)+\n"
+		"	subq.l	#1,%0\n"
+		"	jne	1b\n"
+		"2:	btst	#1,%5\n"
+		"	jeq	4f\n"
+		"3:	"MOVES".w	(%1)+,%3\n"
+		"	move.w	%3,(%2)+\n"
+		"4:	btst	#0,%5\n"
+		"	jeq	6f\n"
+		"5:	"MOVES".b	(%1)+,%3\n"
+		"	move.b  %3,(%2)+\n"
+		"6:\n"
+		"	.section .fixup,\"ax\"\n"
+		"	.even\n"
+		"10:	lsl.l	#2,%0\n"
+		"	btst	#1,%5\n"
+		"	jeq	8f\n"
+		"30:	addq.l	#2,%0\n"
+		"8:	btst	#0,%5\n"
+		"	jeq	6b\n"
+		"50:	addq.l	#1,%0\n"
+		"	jra	6b\n"
+		"	.previous\n"
+		"\n"
+		"	.section __ex_table,\"a\"\n"
+		"	.align	4\n"
+		"	.long	1b,10b\n"
+		"	.long	3b,30b\n"
+		"	.long	5b,50b\n"
+		"	.previous"
+		: "=d" (res), "+a" (from), "+a" (to), "=&d" (tmp)
+		: "0" (n / 4), "d" (n & 3));
+
+	return res;
+}
+EXPORT_SYMBOL(__generic_copy_from_user);
+
+unsigned long __generic_copy_to_user(void __user *to, const void *from,
+				     unsigned long n)
+{
+	unsigned long tmp, res;
+
+	asm volatile ("\n"
+		"	tst.l	%0\n"
+		"	jeq	4f\n"
+		"1:	move.l	(%1)+,%3\n"
+		"2:	"MOVES".l	%3,(%2)+\n"
+		"3:	subq.l	#1,%0\n"
+		"	jne	1b\n"
+		"4:	btst	#1,%5\n"
+		"	jeq	6f\n"
+		"	move.w	(%1)+,%3\n"
+		"5:	"MOVES".w	%3,(%2)+\n"
+		"6:	btst	#0,%5\n"
+		"	jeq	8f\n"
+		"	move.b	(%1)+,%3\n"
+		"7:	"MOVES".b  %3,(%2)+\n"
+		"8:\n"
+		"	.section .fixup,\"ax\"\n"
+		"	.even\n"
+		"20:	lsl.l	#2,%0\n"
+		"50:	add.l	%5,%0\n"
+		"	jra	8b\n"
+		"	.previous\n"
+		"\n"
+		"	.section __ex_table,\"a\"\n"
+		"	.align	4\n"
+		"	.long	2b,20b\n"
+		"	.long	3b,20b\n"
+		"	.long	5b,50b\n"
+		"	.long	6b,50b\n"
+		"	.long	7b,50b\n"
+		"	.long	8b,50b\n"
+		"	.previous"
+		: "=d" (res), "+a" (from), "+a" (to), "=&d" (tmp)
+		: "0" (n / 4), "d" (n & 3));
+
+	return res;
+}
+EXPORT_SYMBOL(__generic_copy_to_user);
+
+/*
+ * Zero Userspace
+ */
+
+unsigned long __clear_user(void __user *to, unsigned long n)
+{
+	unsigned long res;
+
+	asm volatile ("\n"
+		"	tst.l	%0\n"
+		"	jeq	3f\n"
+		"1:	"MOVES".l	%2,(%1)+\n"
+		"2:	subq.l	#1,%0\n"
+		"	jne	1b\n"
+		"3:	btst	#1,%4\n"
+		"	jeq	5f\n"
+		"4:	"MOVES".w	%2,(%1)+\n"
+		"5:	btst	#0,%4\n"
+		"	jeq	7f\n"
+		"6:	"MOVES".b	%2,(%1)\n"
+		"7:\n"
+		"	.section .fixup,\"ax\"\n"
+		"	.even\n"
+		"10:	lsl.l	#2,%0\n"
+		"40:	add.l	%4,%0\n"
+		"	jra	7b\n"
+		"	.previous\n"
+		"\n"
+		"	.section __ex_table,\"a\"\n"
+		"	.align	4\n"
+		"	.long	1b,10b\n"
+		"	.long	2b,10b\n"
+		"	.long	4b,40b\n"
+		"	.long	5b,40b\n"
+		"	.long	6b,40b\n"
+		"	.long	7b,40b\n"
+		"	.previous"
+		: "=d" (res), "+a" (to)
+		: "d" (0), "0" (n / 4), "d" (n & 3));
+
+    return res;
+}
+EXPORT_SYMBOL(__clear_user);