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Message-Id: <20230620140625.1001886-2-longman@redhat.com>
Date: Tue, 20 Jun 2023 10:06:21 -0400
From: Waiman Long <longman@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Jacob Pan <jacob.jun.pan@...ux.intel.com>,
Len Brown <lenb@...nel.org>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
linux-pm@...r.kernel.org, Robin Jarry <rjarry@...hat.com>,
Joe Mario <jmario@...hat.com>, Waiman Long <longman@...hat.com>
Subject: [PATCH v2 1/5] x86/speculation: Provide a debugfs file to dump SPEC_CTRL MSRs
Sometimes it is useful to know the states the SPEC_CTRL MSRs to see what
mitigations are enabled at run time. Provide a new x86/spec_ctrl_msrs
debugfs file to dump the cached versions of the current SPEC_CTRL MSRs.
Signed-off-by: Waiman Long <longman@...hat.com>
---
arch/x86/kernel/cpu/bugs.c | 79 ++++++++++++++++++++++++++++++++++++++
1 file changed, 79 insertions(+)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 182af64387d0..f6e5910a4a2d 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -17,6 +17,7 @@
#include <linux/sched/smt.h>
#include <linux/pgtable.h>
#include <linux/bpf.h>
+#include <linux/debugfs.h>
#include <asm/spec-ctrl.h>
#include <asm/cmdline.h>
@@ -1733,6 +1734,84 @@ void cpu_bugs_smt_update(void)
mutex_unlock(&spec_ctrl_mutex);
}
+#ifdef CONFIG_DEBUG_FS
+/*
+ * Provide a debugfs file to dump SPEC_CTRL MSRs of all the CPUs
+ * Consecutive MSR values are collapsed together if they are the same.
+ */
+static ssize_t spec_ctrl_msrs_read(struct file *file, char __user *user_buf,
+ size_t count, loff_t *ppos)
+{
+ int bufsiz = min(count, PAGE_SIZE);
+ int cpu, prev_cpu, len, cnt = 0;
+ u64 val, prev_val;
+ char *buf;
+
+ /*
+ * The MSRs info should be small enough that the whole buffer is
+ * copied out in one call. However, user space may read it again
+ * to see if there is any data left. Rereading the cached SPEC_CTRL
+ * MSR values may produce a different result causing corruption in
+ * output data. So skipping the call if *ppos is not starting from 0.
+ */
+ if (*ppos)
+ return 0;
+
+ buf = kmalloc(bufsiz, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ for_each_possible_cpu(cpu) {
+ val = per_cpu(x86_spec_ctrl_current, cpu);
+
+ if (!cpu)
+ goto next;
+
+ if (val == prev_val)
+ continue;
+
+ if (prev_cpu == cpu - 1)
+ len = snprintf(buf + cnt, bufsiz - cnt, "CPU %d: 0x%llx\n",
+ prev_cpu, prev_val);
+ else
+ len = snprintf(buf + cnt, bufsiz - cnt, "CPUs %d-%d: 0x%llx\n",
+ prev_cpu, cpu - 1, prev_val);
+
+ cnt += len;
+ if (!len)
+ break; /* Out of buffer */
+next:
+ prev_cpu = cpu;
+ prev_val = val;
+ }
+
+ if (prev_cpu == cpu - 1)
+ cnt += snprintf(buf + cnt, bufsiz - cnt, "CPU %d: 0x%llx\n",
+ prev_cpu, prev_val);
+ else
+ cnt += snprintf(buf + cnt, bufsiz - cnt, "CPUs %d-%d: 0x%llx\n",
+ prev_cpu, cpu - 1, prev_val);
+
+ count = simple_read_from_buffer(user_buf, count, ppos, buf, cnt);
+ kfree(buf);
+ return count;
+}
+
+static const struct file_operations fops_spec_ctrl = {
+ .read = spec_ctrl_msrs_read,
+ .llseek = default_llseek,
+};
+
+static int __init init_spec_ctrl_debugfs(void)
+{
+ if (!debugfs_create_file("spec_ctrl_msrs", 0400, arch_debugfs_dir,
+ NULL, &fops_spec_ctrl))
+ return -ENOMEM;
+ return 0;
+}
+fs_initcall(init_spec_ctrl_debugfs);
+#endif
+
#undef pr_fmt
#define pr_fmt(fmt) "Speculative Store Bypass: " fmt
--
2.31.1
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