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, 41 insertions, 0 deletions

diff --git a/arch/arm/mach-shmobile/timer.c b/arch/arm/mach-shmobile/timer.c
new file mode 100644
index 000000000..2335311b5
--- /dev/null
+++ b/arch/arm/mach-shmobile/timer.c
@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * SH-Mobile Timer
+ *
+ * Copyright (C) 2010  Magnus Damm
+ * Copyright (C) 2002 - 2009  Paul Mundt
+ */
+#include <linux/platform_device.h>
+#include <linux/clocksource.h>
+#include <linux/delay.h>
+#include <linux/of_address.h>
+
+#include "common.h"
+
+void __init shmobile_init_delay(void)
+{
+	struct device_node *np;
+	u32 max_freq = 0;
+
+	for_each_of_cpu_node(np) {
+		u32 freq;
+
+		if (!of_property_read_u32(np, "clock-frequency", &freq))
+			max_freq = max(max_freq, freq);
+	}
+
+	if (!max_freq)
+		return;
+
+	/*
+	 * Calculate a worst-case loops-per-jiffy value
+	 * based on maximum cpu core hz setting and the
+	 * __delay() implementation in arch/arm/lib/delay.S.
+	 *
+	 * This will result in a longer delay than expected
+	 * when the cpu core runs on lower frequencies.
+	 */
+
+	if (!preset_lpj)
+		preset_lpj = max_freq / HZ;
+}