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>

21 files changed, 117 insertions, 0 deletions

diff --git a/scripts/atomic/fallbacks/acquire b/scripts/atomic/fallbacks/acquire
new file mode 100755
index 000000000..4da0cab36
--- /dev/null
+++ b/scripts/atomic/fallbacks/acquire
@@ -0,0 +1,5 @@
+cat <<EOF
+	${ret} ret = arch_${atomic}_${pfx}${name}${sfx}_relaxed(${args});
+	__atomic_acquire_fence();
+	return ret;
+EOF
diff --git a/scripts/atomic/fallbacks/add_negative b/scripts/atomic/fallbacks/add_negative
new file mode 100755
index 000000000..1d3d4ab3a
--- /dev/null
+++ b/scripts/atomic/fallbacks/add_negative
@@ -0,0 +1,3 @@
+cat <<EOF
+	return raw_${atomic}_add_return${order}(i, v) < 0;
+EOF
diff --git a/scripts/atomic/fallbacks/add_unless b/scripts/atomic/fallbacks/add_unless
new file mode 100755
index 000000000..95ecb2b74
--- /dev/null
+++ b/scripts/atomic/fallbacks/add_unless
@@ -0,0 +1,3 @@
+cat << EOF
+	return raw_${atomic}_fetch_add_unless(v, a, u) != u;
+EOF
diff --git a/scripts/atomic/fallbacks/andnot b/scripts/atomic/fallbacks/andnot
new file mode 100755
index 000000000..66760457e
--- /dev/null
+++ b/scripts/atomic/fallbacks/andnot
@@ -0,0 +1,3 @@
+cat <<EOF
+	${retstmt}raw_${atomic}_${pfx}and${sfx}${order}(~i, v);
+EOF
diff --git a/scripts/atomic/fallbacks/cmpxchg b/scripts/atomic/fallbacks/cmpxchg
new file mode 100644
index 000000000..1c8507f62
--- /dev/null
+++ b/scripts/atomic/fallbacks/cmpxchg
@@ -0,0 +1,3 @@
+cat <<EOF
+	return raw_cmpxchg${order}(&v->counter, old, new);
+EOF
diff --git a/scripts/atomic/fallbacks/dec b/scripts/atomic/fallbacks/dec
new file mode 100755
index 000000000..60d286d40
--- /dev/null
+++ b/scripts/atomic/fallbacks/dec
@@ -0,0 +1,3 @@
+cat <<EOF
+	${retstmt}raw_${atomic}_${pfx}sub${sfx}${order}(1, v);
+EOF
diff --git a/scripts/atomic/fallbacks/dec_and_test b/scripts/atomic/fallbacks/dec_and_test
new file mode 100755
index 000000000..3a0278e0d
--- /dev/null
+++ b/scripts/atomic/fallbacks/dec_and_test
@@ -0,0 +1,3 @@
+cat <<EOF
+	return raw_${atomic}_dec_return(v) == 0;
+EOF
diff --git a/scripts/atomic/fallbacks/dec_if_positive b/scripts/atomic/fallbacks/dec_if_positive
new file mode 100755
index 000000000..f65c11b4b
--- /dev/null
+++ b/scripts/atomic/fallbacks/dec_if_positive
@@ -0,0 +1,11 @@
+cat <<EOF
+	${int} dec, c = raw_${atomic}_read(v);
+
+	do {
+		dec = c - 1;
+		if (unlikely(dec < 0))
+			break;
+	} while (!raw_${atomic}_try_cmpxchg(v, &c, dec));
+
+	return dec;
+EOF
diff --git a/scripts/atomic/fallbacks/dec_unless_positive b/scripts/atomic/fallbacks/dec_unless_positive
new file mode 100755
index 000000000..d025361d7
--- /dev/null
+++ b/scripts/atomic/fallbacks/dec_unless_positive
@@ -0,0 +1,10 @@
+cat <<EOF
+	${int} c = raw_${atomic}_read(v);
+
+	do {
+		if (unlikely(c > 0))
+			return false;
+	} while (!raw_${atomic}_try_cmpxchg(v, &c, c - 1));
+
+	return true;
+EOF
diff --git a/scripts/atomic/fallbacks/fence b/scripts/atomic/fallbacks/fence
new file mode 100755
index 000000000..40d5b3976
--- /dev/null
+++ b/scripts/atomic/fallbacks/fence
@@ -0,0 +1,7 @@
+cat <<EOF
+	${ret} ret;
+	__atomic_pre_full_fence();
+	ret = arch_${atomic}_${pfx}${name}${sfx}_relaxed(${args});
+	__atomic_post_full_fence();
+	return ret;
+EOF
diff --git a/scripts/atomic/fallbacks/fetch_add_unless b/scripts/atomic/fallbacks/fetch_add_unless
new file mode 100755
index 000000000..8db7e9e17
--- /dev/null
+++ b/scripts/atomic/fallbacks/fetch_add_unless
@@ -0,0 +1,10 @@
+cat << EOF
+	${int} c = raw_${atomic}_read(v);
+
+	do {
+		if (unlikely(c == u))
+			break;
+	} while (!raw_${atomic}_try_cmpxchg(v, &c, c + a));
+
+	return c;
+EOF
diff --git a/scripts/atomic/fallbacks/inc b/scripts/atomic/fallbacks/inc
new file mode 100755
index 000000000..56c770f59
--- /dev/null
+++ b/scripts/atomic/fallbacks/inc
@@ -0,0 +1,3 @@
+cat <<EOF
+	${retstmt}raw_${atomic}_${pfx}add${sfx}${order}(1, v);
+EOF
diff --git a/scripts/atomic/fallbacks/inc_and_test b/scripts/atomic/fallbacks/inc_and_test
new file mode 100755
index 000000000..7d16a10f2
--- /dev/null
+++ b/scripts/atomic/fallbacks/inc_and_test
@@ -0,0 +1,3 @@
+cat <<EOF
+	return raw_${atomic}_inc_return(v) == 0;
+EOF
diff --git a/scripts/atomic/fallbacks/inc_not_zero b/scripts/atomic/fallbacks/inc_not_zero
new file mode 100755
index 000000000..1fcef1e55
--- /dev/null
+++ b/scripts/atomic/fallbacks/inc_not_zero
@@ -0,0 +1,3 @@
+cat <<EOF
+	return raw_${atomic}_add_unless(v, 1, 0);
+EOF
diff --git a/scripts/atomic/fallbacks/inc_unless_negative b/scripts/atomic/fallbacks/inc_unless_negative
new file mode 100755
index 000000000..7b4b09868
--- /dev/null
+++ b/scripts/atomic/fallbacks/inc_unless_negative
@@ -0,0 +1,10 @@
+cat <<EOF
+	${int} c = raw_${atomic}_read(v);
+
+	do {
+		if (unlikely(c < 0))
+			return false;
+	} while (!raw_${atomic}_try_cmpxchg(v, &c, c + 1));
+
+	return true;
+EOF
diff --git a/scripts/atomic/fallbacks/read_acquire b/scripts/atomic/fallbacks/read_acquire
new file mode 100755
index 000000000..e319862d2
--- /dev/null
+++ b/scripts/atomic/fallbacks/read_acquire
@@ -0,0 +1,12 @@
+cat <<EOF
+	${int} ret;
+
+	if (__native_word(${atomic}_t)) {
+		ret = smp_load_acquire(&(v)->counter);
+	} else {
+		ret = raw_${atomic}_read(v);
+		__atomic_acquire_fence();
+	}
+
+	return ret;
+EOF
diff --git a/scripts/atomic/fallbacks/release b/scripts/atomic/fallbacks/release
new file mode 100755
index 000000000..1e6daf57b
--- /dev/null
+++ b/scripts/atomic/fallbacks/release
@@ -0,0 +1,4 @@
+cat <<EOF
+	__atomic_release_fence();
+	${retstmt}arch_${atomic}_${pfx}${name}${sfx}_relaxed(${args});
+EOF
diff --git a/scripts/atomic/fallbacks/set_release b/scripts/atomic/fallbacks/set_release
new file mode 100755
index 000000000..16a374ae6
--- /dev/null
+++ b/scripts/atomic/fallbacks/set_release
@@ -0,0 +1,8 @@
+cat <<EOF
+	if (__native_word(${atomic}_t)) {
+		smp_store_release(&(v)->counter, i);
+	} else {
+		__atomic_release_fence();
+		raw_${atomic}_set(v, i);
+	}
+EOF
diff --git a/scripts/atomic/fallbacks/sub_and_test b/scripts/atomic/fallbacks/sub_and_test
new file mode 100755
index 000000000..d1f746fe0
--- /dev/null
+++ b/scripts/atomic/fallbacks/sub_and_test
@@ -0,0 +1,3 @@
+cat <<EOF
+	return raw_${atomic}_sub_return(i, v) == 0;
+EOF
diff --git a/scripts/atomic/fallbacks/try_cmpxchg b/scripts/atomic/fallbacks/try_cmpxchg
new file mode 100755
index 000000000..d4da82092
--- /dev/null
+++ b/scripts/atomic/fallbacks/try_cmpxchg
@@ -0,0 +1,7 @@
+cat <<EOF
+	${int} r, o = *old;
+	r = raw_${atomic}_cmpxchg${order}(v, o, new);
+	if (unlikely(r != o))
+		*old = r;
+	return likely(r == o);
+EOF
diff --git a/scripts/atomic/fallbacks/xchg b/scripts/atomic/fallbacks/xchg
new file mode 100644
index 000000000..e4def1e0d
--- /dev/null
+++ b/scripts/atomic/fallbacks/xchg
@@ -0,0 +1,3 @@
+cat <<EOF
+	return raw_xchg${order}(&v->counter, new);
+EOF