linux-kernel - [PATCH v3 06/19] x86/resctrl: Allow the allocator to check if a CLOSID can allocate clean RMID

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Date:   Mon, 20 Mar 2023 17:26:07 +0000
From:   James Morse <james.morse@....com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Babu Moger <Babu.Moger@....com>,
        James Morse <james.morse@....com>,
        shameerali.kolothum.thodi@...wei.com,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        carl@...amperecomputing.com, lcherian@...vell.com,
        bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
        xingxin.hx@...nanolis.org, baolin.wang@...ux.alibaba.com,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com
Subject: [PATCH v3 06/19] x86/resctrl: Allow the allocator to check if a CLOSID can allocate clean RMID

MPAM's PMG bits extend its PARTID space, meaning the same PMG value can be
used for different control groups.

This means once a CLOSID is allocated, all its monitoring ids may still be
dirty, and held in limbo.

Add a helper to allow the CLOSID allocator to check if a CLOSID has dirty
RMID values. This behaviour is enabled by a kconfig option selected by
the architecture, which avoids a pointless search for x86.

Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
Signed-off-by: James Morse <james.morse@....com>

---
Changes since v1:
 * Removed superflous IS_ENABLED().

Changes since v2:
 * Reworded comment over resctrl_closid_is_dirty() to reflect this is all RMID.
---
 arch/x86/kernel/cpu/resctrl/internal.h |  1 +
 arch/x86/kernel/cpu/resctrl/monitor.c  | 36 ++++++++++++++++++++++++++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 17 +++++++-----
 3 files changed, 47 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index e11d9ce943d3..87545e4beb70 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -534,6 +534,7 @@ int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp);
 void rdtgroup_pseudo_lock_remove(struct rdtgroup *rdtgrp);
 struct rdt_domain *get_domain_from_cpu(int cpu, struct rdt_resource *r);
 int closids_supported(void);
+bool resctrl_closid_is_dirty(u32 closid);
 void closid_free(int closid);
 int alloc_rmid(u32 closid);
 void free_rmid(u32 closid, u32 rmid);
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index ca58a433c668..a2ae4be4b2ba 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -363,6 +363,42 @@ static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
 	return ERR_PTR(-ENOSPC);
 }
 
+/**
+ * resctrl_closid_is_dirty - Determine if all RMID associated with this CLOSID
+ *                           are available.
+ * @closid: The CLOSID that is being queried.
+ *
+ * MPAM's equivalent of RMID are per-CLOSID, meaning a freshly allocated CLOSID
+ * may not be able to allocate clean RMID. To avoid this the allocator will
+ * only return clean CLOSID. This is enough for now as it allows MPAM systems
+ * to use resctrl. This suffers from the problem that there may be no CLOSID
+ * where all the RMID are clean, causing the CLOSID allocation to fail.
+ * This can be improved (once MPAM support is upstream) to return the cleanest
+ * CLOSID where PMG=0 is clean. This would allow the CLOSID allocation to
+ * succeed, but subsequent monitor-group allocations may fail.
+ */
+bool resctrl_closid_is_dirty(u32 closid)
+{
+	struct rmid_entry *entry;
+	int i;
+
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	if (!IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
+		return false;
+
+	for (i = 0; i < resctrl_arch_system_num_rmid_idx(); i++) {
+		entry = &rmid_ptrs[i];
+		if (entry->closid != closid)
+			continue;
+
+		if (entry->busy)
+			return true;
+	}
+
+	return false;
+}
+
 /*
  * For MPAM the RMID value is not unique, and has to be considered with
  * the CLOSID. The (CLOSID, RMID) pair is allocated on all domains, which
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index bcd27610bb77..e741bc47bae9 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -93,7 +93,7 @@ void rdt_last_cmd_printf(const char *fmt, ...)
  * - Our choices on how to configure each resource become progressively more
  *   limited as the number of resources grows.
  */
-static int closid_free_map;
+static unsigned long closid_free_map;
 static int closid_free_map_len;
 
 int closids_supported(void)
@@ -119,14 +119,17 @@ static void closid_init(void)
 
 static int closid_alloc(void)
 {
-	u32 closid = ffs(closid_free_map);
+	u32 closid;
 
-	if (closid == 0)
-		return -ENOSPC;
-	closid--;
-	closid_free_map &= ~(1 << closid);
+	for_each_set_bit(closid, &closid_free_map, closid_free_map_len) {
+		if (resctrl_closid_is_dirty(closid))
+			continue;
 
-	return closid;
+		clear_bit(closid, &closid_free_map);
+		return closid;
+	}
+
+	return -ENOSPC;
 }
 
 void closid_free(int closid)
-- 
2.39.2