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, 162 insertions, 0 deletions

diff --git a/arch/m68k/coldfire/pit.c b/arch/m68k/coldfire/pit.c
new file mode 100644
index 000000000..de4eaf8db
--- /dev/null
+++ b/arch/m68k/coldfire/pit.c
@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0
+/***************************************************************************/
+
+/*
+ *	pit.c -- Freescale ColdFire PIT timer. Currently this type of
+ *	         hardware timer only exists in the Freescale ColdFire
+ *		 5270/5271, 5282 and 5208 CPUs. No doubt newer ColdFire
+ *		 family members will probably use it too.
+ *
+ *	Copyright (C) 1999-2008, Greg Ungerer (gerg@snapgear.com)
+ *	Copyright (C) 2001-2004, SnapGear Inc. (www.snapgear.com)
+ */
+
+/***************************************************************************/
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/param.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/clockchips.h>
+#include <asm/machdep.h>
+#include <asm/io.h>
+#include <asm/coldfire.h>
+#include <asm/mcfpit.h>
+#include <asm/mcfsim.h>
+
+/***************************************************************************/
+
+/*
+ *	By default use timer1 as the system clock timer.
+ */
+#define	FREQ	((MCF_CLK / 2) / 64)
+#define	TA(a)	(MCFPIT_BASE1 + (a))
+#define PIT_CYCLES_PER_JIFFY (FREQ / HZ)
+
+static u32 pit_cnt;
+
+/*
+ * Initialize the PIT timer.
+ *
+ * This is also called after resume to bring the PIT into operation again.
+ */
+
+static int cf_pit_set_periodic(struct clock_event_device *evt)
+{
+	mcf_write16(MCFPIT_PCSR_DISABLE, TA(MCFPIT_PCSR));
+	mcf_write16(PIT_CYCLES_PER_JIFFY, TA(MCFPIT_PMR));
+	mcf_write16(MCFPIT_PCSR_EN | MCFPIT_PCSR_PIE |
+		     MCFPIT_PCSR_OVW | MCFPIT_PCSR_RLD |
+		     MCFPIT_PCSR_CLK64, TA(MCFPIT_PCSR));
+	return 0;
+}
+
+static int cf_pit_set_oneshot(struct clock_event_device *evt)
+{
+	mcf_write16(MCFPIT_PCSR_DISABLE, TA(MCFPIT_PCSR));
+	mcf_write16(MCFPIT_PCSR_EN | MCFPIT_PCSR_PIE |
+		     MCFPIT_PCSR_OVW | MCFPIT_PCSR_CLK64, TA(MCFPIT_PCSR));
+	return 0;
+}
+
+static int cf_pit_shutdown(struct clock_event_device *evt)
+{
+	mcf_write16(MCFPIT_PCSR_DISABLE, TA(MCFPIT_PCSR));
+	return 0;
+}
+
+/*
+ * Program the next event in oneshot mode
+ *
+ * Delta is given in PIT ticks
+ */
+static int cf_pit_next_event(unsigned long delta,
+		struct clock_event_device *evt)
+{
+	mcf_write16(delta, TA(MCFPIT_PMR));
+	return 0;
+}
+
+struct clock_event_device cf_pit_clockevent = {
+	.name			= "pit",
+	.features		= CLOCK_EVT_FEAT_PERIODIC |
+				  CLOCK_EVT_FEAT_ONESHOT,
+	.set_state_shutdown	= cf_pit_shutdown,
+	.set_state_periodic	= cf_pit_set_periodic,
+	.set_state_oneshot	= cf_pit_set_oneshot,
+	.set_next_event		= cf_pit_next_event,
+	.shift			= 32,
+	.irq			= MCF_IRQ_PIT1,
+};
+
+
+
+/***************************************************************************/
+
+static irqreturn_t pit_tick(int irq, void *dummy)
+{
+	struct clock_event_device *evt = &cf_pit_clockevent;
+	u16 pcsr;
+
+	/* Reset the ColdFire timer */
+	pcsr = mcf_read16(TA(MCFPIT_PCSR));
+	mcf_write16(pcsr | MCFPIT_PCSR_PIF, TA(MCFPIT_PCSR));
+
+	pit_cnt += PIT_CYCLES_PER_JIFFY;
+	evt->event_handler(evt);
+	return IRQ_HANDLED;
+}
+
+/***************************************************************************/
+
+static u64 pit_read_clk(struct clocksource *cs)
+{
+	unsigned long flags;
+	u32 cycles;
+	u16 pcntr;
+
+	local_irq_save(flags);
+	pcntr = mcf_read16(TA(MCFPIT_PCNTR));
+	cycles = pit_cnt;
+	local_irq_restore(flags);
+
+	return cycles + PIT_CYCLES_PER_JIFFY - pcntr;
+}
+
+/***************************************************************************/
+
+static struct clocksource pit_clk = {
+	.name	= "pit",
+	.rating	= 100,
+	.read	= pit_read_clk,
+	.mask	= CLOCKSOURCE_MASK(32),
+};
+
+/***************************************************************************/
+
+void hw_timer_init(void)
+{
+	int ret;
+
+	cf_pit_clockevent.cpumask = cpumask_of(smp_processor_id());
+	cf_pit_clockevent.mult = div_sc(FREQ, NSEC_PER_SEC, 32);
+	cf_pit_clockevent.max_delta_ns =
+		clockevent_delta2ns(0xFFFF, &cf_pit_clockevent);
+	cf_pit_clockevent.max_delta_ticks = 0xFFFF;
+	cf_pit_clockevent.min_delta_ns =
+		clockevent_delta2ns(0x3f, &cf_pit_clockevent);
+	cf_pit_clockevent.min_delta_ticks = 0x3f;
+	clockevents_register_device(&cf_pit_clockevent);
+
+	ret = request_irq(MCF_IRQ_PIT1, pit_tick, IRQF_TIMER, "timer", NULL);
+	if (ret) {
+		pr_err("Failed to request irq %d (timer): %pe\n", MCF_IRQ_PIT1,
+		       ERR_PTR(ret));
+	}
+
+	clocksource_register_hz(&pit_clk, FREQ);
+}
+
+/***************************************************************************/