linux-kernel - [patch 07/12] mtrr_add_page/mtrr_del_page: check for block interference CPUs

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Date: Tue, 06 Feb 2024 15:49:18 -0300
From: Marcelo Tosatti <mtosatti@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Daniel Bristot de Oliveira <bristot@...nel.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 Valentin Schneider <vschneid@...hat.com>,
 Frederic Weisbecker <frederic@...nel.org>,
 Leonardo Bras <leobras@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>,
 Marcelo Tosatti <mtosatti@...hat.com>
Subject: [patch 07/12] mtrr_add_page/mtrr_del_page: check for block interference CPUs

Check if any online CPU in the system is tagged as
a block interference CPU, and if so return an error
to mtrr_add_page/mtrr_del_page. 

This can avoid interference to such CPUs (while allowing
userspace to handle the failures).

Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>


Index: linux-isolation/arch/x86/kernel/cpu/mtrr/mtrr.c
===================================================================
--- linux-isolation.orig/arch/x86/kernel/cpu/mtrr/mtrr.c
+++ linux-isolation/arch/x86/kernel/cpu/mtrr/mtrr.c
@@ -45,6 +45,7 @@
 #include <linux/smp.h>
 #include <linux/syscore_ops.h>
 #include <linux/rcupdate.h>
+#include <linux/sched/isolation.h>
 
 #include <asm/cacheinfo.h>
 #include <asm/cpufeature.h>
@@ -226,7 +227,7 @@ int mtrr_add_page(unsigned long base, un
 		  unsigned int type, bool increment)
 {
 	unsigned long lbase, lsize;
-	int i, replace, error;
+	int i, replace, error, idx;
 	mtrr_type ltype;
 
 	if (!mtrr_enabled())
@@ -261,6 +262,13 @@ int mtrr_add_page(unsigned long base, un
 	error = -EINVAL;
 	replace = -1;
 
+	idx = block_interf_srcu_read_lock();
+
+	if (cpumask_intersects(block_interf_cpumask, cpu_online_mask)) {
+		block_interf_srcu_read_unlock(idx);
+		return -EPERM;
+	}
+
 	/* No CPU hotplug when we change MTRR entries */
 	cpus_read_lock();
 
@@ -325,6 +333,7 @@ int mtrr_add_page(unsigned long base, un
  out:
 	mutex_unlock(&mtrr_mutex);
 	cpus_read_unlock();
+	block_interf_srcu_read_unlock(idx);
 	return error;
 }
 
@@ -405,11 +414,17 @@ int mtrr_del_page(int reg, unsigned long
 	mtrr_type ltype;
 	unsigned long lbase, lsize;
 	int error = -EINVAL;
+	int idx;
 
 	if (!mtrr_enabled())
 		return -ENODEV;
 
 	max = num_var_ranges;
+	idx = block_interf_srcu_read_lock();
+	if (cpumask_intersects(block_interf_cpumask, cpu_online_mask)) {
+		block_interf_srcu_read_unlock(idx);
+		return -EPERM;
+	}
 	/* No CPU hotplug when we change MTRR entries */
 	cpus_read_lock();
 	mutex_lock(&mtrr_mutex);
@@ -446,6 +461,7 @@ int mtrr_del_page(int reg, unsigned long
  out:
 	mutex_unlock(&mtrr_mutex);
 	cpus_read_unlock();
+	block_interf_srcu_read_unlock(idx);
 	return error;
 }