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, 54 insertions, 0 deletions

diff --git a/arch/mips/rb532/time.c b/arch/mips/rb532/time.c
new file mode 100644
index 000000000..68713dd32
--- /dev/null
+++ b/arch/mips/rb532/time.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Carsten Langgaard, carstenl@mips.com
+ * Copyright (C) 1999,2000 MIPS Technologies, Inc.  All rights reserved.
+ *
+ *  Setting up the clock on the MIPS boards.
+ */
+
+#include <linux/init.h>
+#include <linux/kernel_stat.h>
+#include <linux/ptrace.h>
+#include <linux/sched.h>
+#include <linux/spinlock.h>
+#include <linux/mc146818rtc.h>
+#include <linux/irq.h>
+#include <linux/timex.h>
+
+#include <asm/mipsregs.h>
+#include <asm/time.h>
+#include <asm/mach-rc32434/rc32434.h>
+
+extern unsigned int idt_cpu_freq;
+
+/*
+ * Figure out the r4k offset, the amount to increment the compare
+ * register for each time tick. There is no RTC available.
+ *
+ * The RC32434 counts at half the CPU *core* speed.
+ */
+static unsigned long __init cal_r4koff(void)
+{
+	mips_hpt_frequency = idt_cpu_freq * IDT_CLOCK_MULT / 2;
+
+	return mips_hpt_frequency / HZ;
+}
+
+void __init plat_time_init(void)
+{
+	unsigned int est_freq;
+	unsigned long flags, r4k_offset;
+
+	local_irq_save(flags);
+
+	printk(KERN_INFO "calculating r4koff... ");
+	r4k_offset = cal_r4koff();
+	printk("%08lx(%d)\n", r4k_offset, (int) r4k_offset);
+
+	est_freq = 2 * r4k_offset * HZ;
+	est_freq += 5000;	/* round */
+	est_freq -= est_freq % 10000;
+	printk(KERN_INFO "CPU frequency %d.%02d MHz\n", est_freq / 1000000,
+	       (est_freq % 1000000) * 100 / 1000000);
+	local_irq_restore(flags);
+}