sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

alb_break_llc() decides whether to break LLC preference during active
load balance. It does so by testing that every runnable fair task on the
source rq prefers its LLC:

	env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable

But the two counters cover different sets. nr_pref_llc_running is updated
in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued,
so it follows queued tasks. h_nr_runnable is updated in set_delayed()/
clear_delayed() and drops delay-dequeued tasks.

So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted
in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks,
alb_break_llc() returns false, and active balance is free to pull a task
off its preferred LLC. Active balance only moves runnable tasks, and this
is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB
skips the per-task test in can_migrate_task(). The runnable set is the one
we want.

Fix it on the counter side. A task should be counted in
nr_pref_llc_running exactly while it is both queued on its preferred LLC
(pref_llc_queued) and runnable (!sched_delayed). Define that membership
once in task_pref_llc_runnable(), and adjust the counter only through
pref_llc_running_inc()/pref_llc_running_dec() from the four sites that
change either input: account_llc_enqueue(), account_llc_dequeue(),
set_delayed() and clear_delayed(). Gating every update on the same
predicate keeps the delay, wake and dequeue paths from double-counting
or underflowing; see the comments at those sites for the ordering.

nr_llc_running and sd->llc_counts are not touched and stay on queued
semantics.

Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC")
Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/
Reported-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

1 files changed, 89 insertions, 0 deletions

diff --git a/drivers/crypto/ccp/sev-dev.h b/drivers/crypto/ccp/sev-dev.h
new file mode 100644
index 000000000..d5e596606
--- /dev/null
+++ b/drivers/crypto/ccp/sev-dev.h
@@ -0,0 +1,89 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * AMD Platform Security Processor (PSP) interface driver
+ *
+ * Copyright (C) 2017-2019 Advanced Micro Devices, Inc.
+ *
+ * Author: Brijesh Singh <brijesh.singh@amd.com>
+ */
+
+#ifndef __SEV_DEV_H__
+#define __SEV_DEV_H__
+
+#include <linux/device.h>
+#include <linux/spinlock.h>
+#include <linux/mutex.h>
+#include <linux/list.h>
+#include <linux/wait.h>
+#include <linux/dmapool.h>
+#include <linux/hw_random.h>
+#include <linux/bitops.h>
+#include <linux/interrupt.h>
+#include <linux/irqreturn.h>
+#include <linux/dmaengine.h>
+#include <linux/psp-sev.h>
+#include <linux/miscdevice.h>
+#include <linux/capability.h>
+
+#define SEV_CMDRESP_CMD			GENMASK(26, 16)
+#define SEV_CMD_COMPLETE		BIT(1)
+#define SEV_CMDRESP_IOC			BIT(0)
+
+struct sev_misc_dev {
+	struct kref refcount;
+	struct miscdevice misc;
+};
+
+struct sev_tio_status;
+
+struct sev_device {
+	struct device *dev;
+	struct psp_device *psp;
+
+	void __iomem *io_regs;
+
+	struct sev_vdata *vdata;
+
+	unsigned int int_rcvd;
+	wait_queue_head_t int_queue;
+	struct sev_misc_dev *misc;
+
+	u8 api_major;
+	u8 api_minor;
+	u8 build;
+
+	void *cmd_buf;
+	void *cmd_buf_backup;
+	bool cmd_buf_active;
+	bool cmd_buf_backup_active;
+
+	bool snp_initialized;
+
+	struct kobject *sev_kobj;
+	struct kobject *verify_mit;
+
+	struct sev_user_data_status sev_plat_status;
+
+	struct sev_user_data_snp_status snp_plat_status;
+	struct snp_feature_info snp_feat_info_0;
+
+	struct tsm_dev *tsmdev;
+	struct sev_tio_status *tio_status;
+};
+
+int sev_dev_init(struct psp_device *psp);
+void sev_dev_destroy(struct psp_device *psp);
+
+int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret);
+
+void sev_pci_init(void);
+void sev_pci_exit(void);
+
+struct page *snp_alloc_hv_fixed_pages(unsigned int num_2mb_pages);
+void snp_free_hv_fixed_pages(struct page *page);
+
+void sev_tsm_init_locked(struct sev_device *sev, void *tio_status_page);
+void sev_tsm_uninit(struct sev_device *sev);
+int sev_tio_cmd_buffer_len(int cmd);
+
+#endif /* __SEV_DEV_H */