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, 123 insertions, 0 deletions

diff --git a/net/sunrpc/timer.c b/net/sunrpc/timer.c
new file mode 100644
index 000000000..81ae35b37
--- /dev/null
+++ b/net/sunrpc/timer.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * linux/net/sunrpc/timer.c
+ *
+ * Estimate RPC request round trip time.
+ *
+ * Based on packet round-trip and variance estimator algorithms described
+ * in appendix A of "Congestion Avoidance and Control" by Van Jacobson
+ * and Michael J. Karels (ACM Computer Communication Review; Proceedings
+ * of the Sigcomm '88 Symposium in Stanford, CA, August, 1988).
+ *
+ * This RTT estimator is used only for RPC over datagram protocols.
+ *
+ * Copyright (C) 2002 Trond Myklebust <trond.myklebust@fys.uio.no>
+ */
+
+#include <asm/param.h>
+
+#include <linux/types.h>
+#include <linux/unistd.h>
+#include <linux/module.h>
+
+#include <linux/sunrpc/clnt.h>
+
+#define RPC_RTO_MAX (60*HZ)
+#define RPC_RTO_INIT (HZ/5)
+#define RPC_RTO_MIN (HZ/10)
+
+/**
+ * rpc_init_rtt - Initialize an RPC RTT estimator context
+ * @rt: context to initialize
+ * @timeo: initial timeout value, in jiffies
+ *
+ */
+void rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
+{
+	unsigned long init = 0;
+	unsigned int i;
+
+	rt->timeo = timeo;
+
+	if (timeo > RPC_RTO_INIT)
+		init = (timeo - RPC_RTO_INIT) << 3;
+	for (i = 0; i < 5; i++) {
+		rt->srtt[i] = init;
+		rt->sdrtt[i] = RPC_RTO_INIT;
+		rt->ntimeouts[i] = 0;
+	}
+}
+EXPORT_SYMBOL_GPL(rpc_init_rtt);
+
+/**
+ * rpc_update_rtt - Update an RPC RTT estimator context
+ * @rt: context to update
+ * @timer: timer array index (request type)
+ * @m: recent actual RTT, in jiffies
+ *
+ * NB: When computing the smoothed RTT and standard deviation,
+ *     be careful not to produce negative intermediate results.
+ */
+void rpc_update_rtt(struct rpc_rtt *rt, unsigned int timer, long m)
+{
+	long *srtt, *sdrtt;
+
+	if (timer-- == 0)
+		return;
+
+	/* jiffies wrapped; ignore this one */
+	if (m < 0)
+		return;
+
+	if (m == 0)
+		m = 1L;
+
+	srtt = (long *)&rt->srtt[timer];
+	m -= *srtt >> 3;
+	*srtt += m;
+
+	if (m < 0)
+		m = -m;
+
+	sdrtt = (long *)&rt->sdrtt[timer];
+	m -= *sdrtt >> 2;
+	*sdrtt += m;
+
+	/* Set lower bound on the variance */
+	if (*sdrtt < RPC_RTO_MIN)
+		*sdrtt = RPC_RTO_MIN;
+}
+EXPORT_SYMBOL_GPL(rpc_update_rtt);
+
+/**
+ * rpc_calc_rto - Provide an estimated timeout value
+ * @rt: context to use for calculation
+ * @timer: timer array index (request type)
+ *
+ * Estimate RTO for an NFS RPC sent via an unreliable datagram.  Use
+ * the mean and mean deviation of RTT for the appropriate type of RPC
+ * for frequently issued RPCs, and a fixed default for the others.
+ *
+ * The justification for doing "other" this way is that these RPCs
+ * happen so infrequently that timer estimation would probably be
+ * stale.  Also, since many of these RPCs are non-idempotent, a
+ * conservative timeout is desired.
+ *
+ * getattr, lookup,
+ * read, write, commit     - A+4D
+ * other                   - timeo
+ */
+unsigned long rpc_calc_rto(struct rpc_rtt *rt, unsigned int timer)
+{
+	unsigned long res;
+
+	if (timer-- == 0)
+		return rt->timeo;
+
+	res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
+	if (res > RPC_RTO_MAX)
+		res = RPC_RTO_MAX;
+
+	return res;
+}
+EXPORT_SYMBOL_GPL(rpc_calc_rto);