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, 75 insertions, 0 deletions

diff --git a/arch/arc/lib/strcmp-archs.S b/arch/arc/lib/strcmp-archs.S
new file mode 100644
index 000000000..7cffb3717
--- /dev/null
+++ b/arch/arc/lib/strcmp-archs.S
@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2014-15 Synopsys, Inc. (www.synopsys.com)
+ */
+
+#include <linux/linkage.h>
+
+ENTRY_CFI(strcmp)
+	or	r2, r0, r1
+	bmsk_s	r2, r2, 1
+	brne	r2, 0, @.Lcharloop
+
+;;; s1 and s2 are word aligned
+	ld.ab	r2, [r0, 4]
+
+	mov_s	r12, 0x01010101
+	ror	r11, r12
+	.align  4
+.LwordLoop:
+	ld.ab	r3, [r1, 4]
+	;; Detect NULL char in str1
+	sub	r4, r2, r12
+	ld.ab	r5, [r0, 4]
+	bic	r4, r4, r2
+	and	r4, r4, r11
+	brne.d.nt	r4, 0, .LfoundNULL
+	;; Check if the read locations are the same
+	cmp	r2, r3
+	beq.d	.LwordLoop
+	mov.eq	r2, r5
+
+	;; A match is found, spot it out
+#ifdef __LITTLE_ENDIAN__
+	swape	r3, r3
+	mov_s	r0, 1
+	swape	r2, r2
+#else
+	mov_s	r0, 1
+#endif
+	cmp_s	r2, r3
+	j_s.d	[blink]
+	bset.lo	r0, r0, 31
+
+	.align 4
+.LfoundNULL:
+#ifdef __BIG_ENDIAN__
+	swape	r4, r4
+	swape	r2, r2
+	swape	r3, r3
+#endif
+	;; Find null byte
+	ffs	r0, r4
+	bmsk	r2, r2, r0
+	bmsk	r3, r3, r0
+	swape	r2, r2
+	swape	r3, r3
+	;; make the return value
+	sub.f	r0, r2, r3
+	mov.hi	r0, 1
+	j_s.d	[blink]
+	bset.lo	r0, r0, 31
+
+	.align 4
+.Lcharloop:
+	ldb.ab	r2, [r0, 1]
+	ldb.ab	r3, [r1, 1]
+	nop
+	breq	r2, 0, .Lcmpend
+	breq	r2, r3, .Lcharloop
+
+	.align 4
+.Lcmpend:
+	j_s.d	[blink]
+	sub	r0, r2, r3
+END_CFI(strcmp)