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, 273 insertions, 0 deletions

diff --git a/include/net/codel_impl.h b/include/net/codel_impl.h
new file mode 100644
index 000000000..2c1f0ec30
--- /dev/null
+++ b/include/net/codel_impl.h
@@ -0,0 +1,273 @@
+#ifndef __NET_SCHED_CODEL_IMPL_H
+#define __NET_SCHED_CODEL_IMPL_H
+
+/*
+ * Codel - The Controlled-Delay Active Queue Management algorithm
+ *
+ *  Copyright (C) 2011-2012 Kathleen Nichols <nichols@pollere.com>
+ *  Copyright (C) 2011-2012 Van Jacobson <van@pollere.net>
+ *  Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net>
+ *  Copyright (C) 2012,2015 Eric Dumazet <edumazet@google.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions, and the following disclaimer,
+ *    without modification.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The names of the authors may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * Alternatively, provided that this notice is retained in full, this
+ * software may be distributed under the terms of the GNU General
+ * Public License ("GPL") version 2, in which case the provisions of the
+ * GPL apply INSTEAD OF those given above.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ */
+
+/* Controlling Queue Delay (CoDel) algorithm
+ * =========================================
+ * Source : Kathleen Nichols and Van Jacobson
+ * http://queue.acm.org/detail.cfm?id=2209336
+ *
+ * Implemented on linux by Dave Taht and Eric Dumazet
+ */
+
+#include <net/inet_ecn.h>
+
+static void codel_params_init(struct codel_params *params)
+{
+	params->interval = MS2TIME(100);
+	params->target = MS2TIME(5);
+	params->ce_threshold = CODEL_DISABLED_THRESHOLD;
+	params->ce_threshold_mask = 0;
+	params->ce_threshold_selector = 0;
+	params->ecn = false;
+}
+
+static void codel_vars_init(struct codel_vars *vars)
+{
+	memset(vars, 0, sizeof(*vars));
+}
+
+static void codel_stats_init(struct codel_stats *stats)
+{
+	stats->maxpacket = 0;
+}
+
+/*
+ * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
+ * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
+ *
+ * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
+ */
+static void codel_Newton_step(struct codel_vars *vars)
+{
+	u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
+	u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
+	u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
+
+	val >>= 2; /* avoid overflow in following multiply */
+	val = (val * invsqrt) >> (32 - 2 + 1);
+
+	vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
+}
+
+/*
+ * CoDel control_law is t + interval/sqrt(count)
+ * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
+ * both sqrt() and divide operation.
+ */
+static codel_time_t codel_control_law(codel_time_t t,
+				      codel_time_t interval,
+				      u32 rec_inv_sqrt)
+{
+	return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
+}
+
+static bool codel_should_drop(const struct sk_buff *skb,
+			      void *ctx,
+			      struct codel_vars *vars,
+			      struct codel_params *params,
+			      struct codel_stats *stats,
+			      codel_skb_len_t skb_len_func,
+			      codel_skb_time_t skb_time_func,
+			      u32 *backlog,
+			      codel_time_t now)
+{
+	bool ok_to_drop;
+	u32 skb_len;
+
+	if (!skb) {
+		vars->first_above_time = 0;
+		return false;
+	}
+
+	skb_len = skb_len_func(skb);
+	WRITE_ONCE(vars->ldelay, now - skb_time_func(skb));
+
+	if (unlikely(skb_len > stats->maxpacket))
+		WRITE_ONCE(stats->maxpacket, skb_len);
+
+	if (codel_time_before(vars->ldelay, params->target) ||
+	    *backlog <= params->mtu) {
+		/* went below - stay below for at least interval */
+		vars->first_above_time = 0;
+		return false;
+	}
+	ok_to_drop = false;
+	if (vars->first_above_time == 0) {
+		/* just went above from below. If we stay above
+		 * for at least interval we'll say it's ok to drop
+		 */
+		vars->first_above_time = now + params->interval;
+	} else if (codel_time_after(now, vars->first_above_time)) {
+		ok_to_drop = true;
+	}
+	return ok_to_drop;
+}
+
+static struct sk_buff *codel_dequeue(void *ctx,
+				     u32 *backlog,
+				     struct codel_params *params,
+				     struct codel_vars *vars,
+				     struct codel_stats *stats,
+				     codel_skb_len_t skb_len_func,
+				     codel_skb_time_t skb_time_func,
+				     codel_skb_drop_t drop_func,
+				     codel_skb_dequeue_t dequeue_func)
+{
+	struct sk_buff *skb = dequeue_func(vars, ctx);
+	codel_time_t now;
+	bool drop;
+
+	if (!skb) {
+		vars->first_above_time = 0;
+		WRITE_ONCE(vars->dropping, false);
+		return skb;
+	}
+	now = codel_get_time();
+	drop = codel_should_drop(skb, ctx, vars, params, stats,
+				 skb_len_func, skb_time_func, backlog, now);
+	if (vars->dropping) {
+		if (!drop) {
+			/* sojourn time below target - leave dropping state */
+			WRITE_ONCE(vars->dropping, false);
+		} else if (codel_time_after_eq(now, vars->drop_next)) {
+			/* It's time for the next drop. Drop the current
+			 * packet and dequeue the next. The dequeue might
+			 * take us out of dropping state.
+			 * If not, schedule the next drop.
+			 * A large backlog might result in drop rates so high
+			 * that the next drop should happen now,
+			 * hence the while loop.
+			 */
+			while (vars->dropping &&
+			       codel_time_after_eq(now, vars->drop_next)) {
+				/* dont care of possible wrap
+				 * since there is no more divide.
+				 */
+				WRITE_ONCE(vars->count, vars->count + 1);
+				codel_Newton_step(vars);
+				if (params->ecn && INET_ECN_set_ce(skb)) {
+					WRITE_ONCE(stats->ecn_mark,
+						   stats->ecn_mark + 1);
+					WRITE_ONCE(vars->drop_next,
+						codel_control_law(vars->drop_next,
+								  params->interval,
+								  vars->rec_inv_sqrt));
+					goto end;
+				}
+				stats->drop_len += skb_len_func(skb);
+				drop_func(skb, ctx);
+				stats->drop_count++;
+				skb = dequeue_func(vars, ctx);
+				if (!codel_should_drop(skb, ctx,
+						       vars, params, stats,
+						       skb_len_func,
+						       skb_time_func,
+						       backlog, now)) {
+					/* leave dropping state */
+					WRITE_ONCE(vars->dropping, false);
+				} else {
+					/* and schedule the next drop */
+					WRITE_ONCE(vars->drop_next,
+						codel_control_law(vars->drop_next,
+								  params->interval,
+								  vars->rec_inv_sqrt));
+				}
+			}
+		}
+	} else if (drop) {
+		u32 delta;
+
+		if (params->ecn && INET_ECN_set_ce(skb)) {
+			WRITE_ONCE(stats->ecn_mark, stats->ecn_mark + 1);
+		} else {
+			stats->drop_len += skb_len_func(skb);
+			drop_func(skb, ctx);
+			stats->drop_count++;
+
+			skb = dequeue_func(vars, ctx);
+			drop = codel_should_drop(skb, ctx, vars, params,
+						 stats, skb_len_func,
+						 skb_time_func, backlog, now);
+		}
+		WRITE_ONCE(vars->dropping, true);
+		/* if min went above target close to when we last went below it
+		 * assume that the drop rate that controlled the queue on the
+		 * last cycle is a good starting point to control it now.
+		 */
+		delta = vars->count - vars->lastcount;
+		if (delta > 1 &&
+		    codel_time_before(now - vars->drop_next,
+				      16 * params->interval)) {
+			WRITE_ONCE(vars->count, delta);
+			/* we dont care if rec_inv_sqrt approximation
+			 * is not very precise :
+			 * Next Newton steps will correct it quadratically.
+			 */
+			codel_Newton_step(vars);
+		} else {
+			WRITE_ONCE(vars->count, 1);
+			vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
+		}
+		WRITE_ONCE(vars->lastcount, vars->count);
+		WRITE_ONCE(vars->drop_next,
+			   codel_control_law(now, params->interval,
+					     vars->rec_inv_sqrt));
+	}
+end:
+	if (skb && codel_time_after(vars->ldelay, params->ce_threshold)) {
+		bool set_ce = true;
+
+		if (params->ce_threshold_mask) {
+			int dsfield = skb_get_dsfield(skb);
+
+			set_ce = (dsfield >= 0 &&
+				  (((u8)dsfield & params->ce_threshold_mask) ==
+				   params->ce_threshold_selector));
+		}
+		if (set_ce && INET_ECN_set_ce(skb))
+			WRITE_ONCE(stats->ce_mark, stats->ce_mark + 1);
+	}
+	return skb;
+}
+
+#endif