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, 172 insertions, 0 deletions

diff --git a/arch/mips/dec/time.c b/arch/mips/dec/time.c
new file mode 100644
index 000000000..c38686f89
--- /dev/null
+++ b/arch/mips/dec/time.c
@@ -0,0 +1,172 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  Copyright (C) 1991, 1992, 1995  Linus Torvalds
+ *  Copyright (C) 2000, 2003  Maciej W. Rozycki
+ *
+ * This file contains the time handling details for PC-style clocks as
+ * found in some MIPS systems.
+ *
+ */
+#include <linux/bcd.h>
+#include <linux/init.h>
+#include <linux/mc146818rtc.h>
+#include <linux/param.h>
+
+#include <asm/cpu-features.h>
+#include <asm/ds1287.h>
+#include <asm/time.h>
+#include <asm/dec/interrupts.h>
+#include <asm/dec/ioasic.h>
+#include <asm/dec/machtype.h>
+
+void read_persistent_clock64(struct timespec64 *ts)
+{
+	unsigned int year, mon, day, hour, min, sec, real_year;
+	unsigned long flags;
+
+	spin_lock_irqsave(&rtc_lock, flags);
+
+	do {
+		sec = CMOS_READ(RTC_SECONDS);
+		min = CMOS_READ(RTC_MINUTES);
+		hour = CMOS_READ(RTC_HOURS);
+		day = CMOS_READ(RTC_DAY_OF_MONTH);
+		mon = CMOS_READ(RTC_MONTH);
+		year = CMOS_READ(RTC_YEAR);
+		/*
+		 * The PROM will reset the year to either '72 or '73.
+		 * Therefore we store the real year separately, in one
+		 * of unused BBU RAM locations.
+		 */
+		real_year = CMOS_READ(RTC_DEC_YEAR);
+	} while (sec != CMOS_READ(RTC_SECONDS));
+
+	spin_unlock_irqrestore(&rtc_lock, flags);
+
+	if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
+		sec = bcd2bin(sec);
+		min = bcd2bin(min);
+		hour = bcd2bin(hour);
+		day = bcd2bin(day);
+		mon = bcd2bin(mon);
+		year = bcd2bin(year);
+	}
+
+	year += real_year - 72 + 2000;
+
+	ts->tv_sec = mktime64(year, mon, day, hour, min, sec);
+	ts->tv_nsec = 0;
+}
+
+/*
+ * In order to set the CMOS clock precisely, update_persistent_clock64 has to
+ * be called 500 ms after the second nowtime has started, because when
+ * nowtime is written into the registers of the CMOS clock, it will
+ * jump to the next second precisely 500 ms later.  Check the Dallas
+ * DS1287 data sheet for details.
+ */
+int update_persistent_clock64(struct timespec64 now)
+{
+	time64_t nowtime = now.tv_sec;
+	int retval = 0;
+	int real_seconds, real_minutes, cmos_minutes;
+	unsigned char save_control, save_freq_select;
+
+	/* irq are locally disabled here */
+	spin_lock(&rtc_lock);
+	/* tell the clock it's being set */
+	save_control = CMOS_READ(RTC_CONTROL);
+	CMOS_WRITE((save_control | RTC_SET), RTC_CONTROL);
+
+	/* stop and reset prescaler */
+	save_freq_select = CMOS_READ(RTC_FREQ_SELECT);
+	CMOS_WRITE((save_freq_select | RTC_DIV_RESET2), RTC_FREQ_SELECT);
+
+	cmos_minutes = CMOS_READ(RTC_MINUTES);
+	if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
+		cmos_minutes = bcd2bin(cmos_minutes);
+
+	/*
+	 * since we're only adjusting minutes and seconds,
+	 * don't interfere with hour overflow. This avoids
+	 * messing with unknown time zones but requires your
+	 * RTC not to be off by more than 15 minutes
+	 */
+	real_minutes = div_s64_rem(nowtime, 60, &real_seconds);
+	if (((abs(real_minutes - cmos_minutes) + 15) / 30) & 1)
+		real_minutes += 30;	/* correct for half hour time zone */
+	real_minutes %= 60;
+
+	if (abs(real_minutes - cmos_minutes) < 30) {
+		if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
+			real_seconds = bin2bcd(real_seconds);
+			real_minutes = bin2bcd(real_minutes);
+		}
+		CMOS_WRITE(real_seconds, RTC_SECONDS);
+		CMOS_WRITE(real_minutes, RTC_MINUTES);
+	} else {
+		printk_once(KERN_NOTICE
+		       "set_rtc_mmss: can't update from %d to %d\n",
+		       cmos_minutes, real_minutes);
+		retval = -1;
+	}
+
+	/* The following flags have to be released exactly in this order,
+	 * otherwise the DS1287 will not reset the oscillator and will not
+	 * update precisely 500 ms later.  You won't find this mentioned
+	 * in the Dallas Semiconductor data sheets, but who believes data
+	 * sheets anyway ...                           -- Markus Kuhn
+	 */
+	CMOS_WRITE(save_control, RTC_CONTROL);
+	CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
+	spin_unlock(&rtc_lock);
+
+	return retval;
+}
+
+void __init plat_time_init(void)
+{
+	int ioasic_clock = 0;
+	u32 start, end;
+	int i = HZ / 8;
+
+	/* Set up the rate of periodic DS1287 interrupts. */
+	ds1287_set_base_clock(HZ);
+
+	/* On some I/O ASIC systems we have the I/O ASIC's counter.  */
+	if (IOASIC)
+		ioasic_clock = dec_ioasic_clocksource_init() == 0;
+	if (cpu_has_counter) {
+		ds1287_timer_state();
+		while (!ds1287_timer_state())
+			;
+
+		start = read_c0_count();
+
+		while (i--)
+			while (!ds1287_timer_state())
+				;
+
+		end = read_c0_count();
+
+		mips_hpt_frequency = (end - start) * 8;
+		printk(KERN_INFO "MIPS counter frequency %dHz\n",
+			mips_hpt_frequency);
+
+		/*
+		 * All R4k DECstations suffer from the CP0 Count erratum,
+		 * so we can't use the timer as a clock source, and a clock
+		 * event both at a time.  An accurate wall clock is more
+		 * important than a high-precision interval timer so only
+		 * use the timer as a clock source, and not a clock event
+		 * if there's no I/O ASIC counter available to serve as a
+		 * clock source.
+		 */
+		if (!ioasic_clock) {
+			init_r4k_clocksource();
+			mips_hpt_frequency = 0;
+		}
+	}
+
+	ds1287_clockevent_init(dec_interrupt[DEC_IRQ_RTC]);
+}