KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 148 insertions, 0 deletions

diff --git a/drivers/macintosh/windfarm_pid.c b/drivers/macintosh/windfarm_pid.c
new file mode 100644
index 000000000..bb31b0e93
--- /dev/null
+++ b/drivers/macintosh/windfarm_pid.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Windfarm PowerMac thermal control. Generic PID helpers
+ *
+ * (c) Copyright 2005 Benjamin Herrenschmidt, IBM Corp.
+ *                    <benh@kernel.crashing.org>
+ */
+
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/module.h>
+
+#include "windfarm_pid.h"
+
+#undef DEBUG
+
+#ifdef DEBUG
+#define DBG(args...)	printk(args)
+#else
+#define DBG(args...)	do { } while(0)
+#endif
+
+void wf_pid_init(struct wf_pid_state *st, struct wf_pid_param *param)
+{
+	memset(st, 0, sizeof(struct wf_pid_state));
+	st->param = *param;
+	st->first = 1;
+}
+EXPORT_SYMBOL_GPL(wf_pid_init);
+
+s32 wf_pid_run(struct wf_pid_state *st, s32 new_sample)
+{
+	s64	error, integ, deriv;
+	s32	target;
+	int	i, hlen = st->param.history_len;
+
+	/* Calculate error term */
+	error = new_sample - st->param.itarget;
+
+	/* Get samples into our history buffer */
+	if (st->first) {
+		for (i = 0; i < hlen; i++) {
+			st->samples[i] = new_sample;
+			st->errors[i] = error;
+		}
+		st->first = 0;
+		st->index = 0;
+	} else {
+		st->index = (st->index + 1) % hlen;
+		st->samples[st->index] = new_sample;
+		st->errors[st->index] = error;
+	}
+
+	/* Calculate integral term */
+	for (i = 0, integ = 0; i < hlen; i++)
+		integ += st->errors[(st->index + hlen - i) % hlen];
+	integ *= st->param.interval;
+
+	/* Calculate derivative term */
+	deriv = st->errors[st->index] -
+		st->errors[(st->index + hlen - 1) % hlen];
+	deriv /= st->param.interval;
+
+	/* Calculate target */
+	target = (s32)((integ * (s64)st->param.gr + deriv * (s64)st->param.gd +
+		  error * (s64)st->param.gp) >> 36);
+	if (st->param.additive)
+		target += st->target;
+	target = max(target, st->param.min);
+	target = min(target, st->param.max);
+	st->target = target;
+
+	return st->target;
+}
+EXPORT_SYMBOL_GPL(wf_pid_run);
+
+void wf_cpu_pid_init(struct wf_cpu_pid_state *st,
+		     struct wf_cpu_pid_param *param)
+{
+	memset(st, 0, sizeof(struct wf_cpu_pid_state));
+	st->param = *param;
+	st->first = 1;
+}
+EXPORT_SYMBOL_GPL(wf_cpu_pid_init);
+
+s32 wf_cpu_pid_run(struct wf_cpu_pid_state *st, s32 new_power, s32 new_temp)
+{
+	s64	integ, deriv, prop;
+	s32	error, target, sval, adj;
+	int	i, hlen = st->param.history_len;
+
+	/* Calculate error term */
+	error = st->param.pmaxadj - new_power;
+
+	/* Get samples into our history buffer */
+	if (st->first) {
+		for (i = 0; i < hlen; i++) {
+			st->powers[i] = new_power;
+			st->errors[i] = error;
+		}
+		st->temps[0] = st->temps[1] = new_temp;
+		st->first = 0;
+		st->index = st->tindex = 0;
+	} else {
+		st->index = (st->index + 1) % hlen;
+		st->powers[st->index] = new_power;
+		st->errors[st->index] = error;
+		st->tindex = (st->tindex + 1) % 2;
+		st->temps[st->tindex] = new_temp;
+	}
+
+	/* Calculate integral term */
+	for (i = 0, integ = 0; i < hlen; i++)
+		integ += st->errors[(st->index + hlen - i) % hlen];
+	integ *= st->param.interval;
+	integ *= st->param.gr;
+	sval = st->param.tmax - (s32)(integ >> 20);
+	adj = min(st->param.ttarget, sval);
+
+	DBG("integ: %lx, sval: %lx, adj: %lx\n", integ, sval, adj);
+
+	/* Calculate derivative term */
+	deriv = st->temps[st->tindex] -
+		st->temps[(st->tindex + 2 - 1) % 2];
+	deriv /= st->param.interval;
+	deriv *= st->param.gd;
+
+	/* Calculate proportional term */
+	prop = st->last_delta = (new_temp - adj);
+	prop *= st->param.gp;
+
+	DBG("deriv: %lx, prop: %lx\n", deriv, prop);
+
+	/* Calculate target */
+	target = st->target + (s32)((deriv + prop) >> 36);
+	target = max(target, st->param.min);
+	target = min(target, st->param.max);
+	st->target = target;
+
+	return st->target;
+}
+EXPORT_SYMBOL_GPL(wf_cpu_pid_run);
+
+MODULE_AUTHOR("Benjamin Herrenschmidt <benh@kernel.crashing.org>");
+MODULE_DESCRIPTION("PID algorithm for PowerMacs thermal control");
+MODULE_LICENSE("GPL");