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Message-Id: <20240703115620.25772-1-jgross@suse.com>
Date: Wed, 3 Jul 2024 13:56:20 +0200
From: Juergen Gross <jgross@...e.com>
To: linux-kernel@...r.kernel.org,
x86@...nel.org,
linux-doc@...r.kernel.org
Cc: Juergen Gross <jgross@...e.com>,
Jonathan Corbet <corbet@....net>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
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>,
xen-devel@...ts.xenproject.org
Subject: [PATCH] xen: make multicall debug boot time selectable
Today Xen multicall debugging needs to be enabled via modifying a
define in a source file for getting debug data of multicall errors
encountered by users.
Switch multicall debugging to depend on a boot parameter "xen_mc_debug"
instead, enabling affected users to boot with the new parameter set in
order to get better diagnostics.
Add printing all arguments of a single call for better diagnostics.
Signed-off-by: Juergen Gross <jgross@...e.com>
---
.../admin-guide/kernel-parameters.txt | 6 +
arch/x86/xen/multicalls.c | 120 ++++++++++++++----
2 files changed, 99 insertions(+), 27 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 27ec49af1bf2..b33d048e01d8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -7427,6 +7427,12 @@
Crash from Xen panic notifier, without executing late
panic() code such as dumping handler.
+ xen_mc_debug [X86,XEN,EARLY]
+ Enable multicall debugging when running as a Xen PV guest.
+ Enabling this feature will reduce performance a little
+ bit, so it should only be enabled for obtaining extended
+ debug data in case of multicall errors.
+
xen_msr_safe= [X86,XEN,EARLY]
Format: <bool>
Select whether to always use non-faulting (safe) MSR
diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c
index 07054572297f..abea216f07f4 100644
--- a/arch/x86/xen/multicalls.c
+++ b/arch/x86/xen/multicalls.c
@@ -23,6 +23,8 @@
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/debugfs.h>
+#include <linux/jump_label.h>
+#include <linux/printk.h>
#include <asm/xen/hypercall.h>
@@ -31,18 +33,12 @@
#define MC_BATCH 32
-#define MC_DEBUG 0
-
#define MC_ARGS (MC_BATCH * 16)
struct mc_buffer {
unsigned mcidx, argidx, cbidx;
struct multicall_entry entries[MC_BATCH];
-#if MC_DEBUG
- struct multicall_entry debug[MC_BATCH];
- void *caller[MC_BATCH];
-#endif
unsigned char args[MC_ARGS];
struct callback {
void (*fn)(void *);
@@ -50,13 +46,84 @@ struct mc_buffer {
} callbacks[MC_BATCH];
};
+struct mc_debug_data {
+ struct multicall_entry debug[MC_BATCH];
+ void *caller[MC_BATCH];
+ size_t argsz[MC_BATCH];
+};
+
static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
+static struct mc_debug_data __percpu *mc_debug_data;
+static struct mc_debug_data mc_debug_data_early __initdata;
DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
+static struct static_key mc_debug __ro_after_init;
+static bool mc_debug_enabled __initdata;
+
+static int __init xen_parse_mc_debug(char *arg)
+{
+ mc_debug_enabled = true;
+ static_key_slow_inc(&mc_debug);
+
+ return 0;
+}
+early_param("xen_mc_debug", xen_parse_mc_debug);
+
+static int __init mc_debug_enable(void)
+{
+ struct mc_debug_data __percpu *mcdb;
+ unsigned long flags;
+
+ if (!mc_debug_enabled)
+ return 0;
+
+ mcdb = alloc_percpu(struct mc_debug_data);
+ if (!mcdb) {
+ pr_err("xen_mc_debug inactive\n");
+ static_key_slow_dec(&mc_debug);
+ return -ENOMEM;
+ }
+
+ /* Be careful when switching to percpu debug data. */
+ local_irq_save(flags);
+ xen_mc_flush();
+ mc_debug_data = mcdb;
+ local_irq_restore(flags);
+
+ pr_info("xen_mc_debug active\n");
+
+ return 0;
+}
+early_initcall(mc_debug_enable);
+
+static void print_debug_data(struct mc_buffer *b, struct mc_debug_data *mcdb,
+ int idx)
+{
+ unsigned int arg;
+
+ pr_err(" call %2d: op=%lu result=%ld caller=%pS", idx + 1,
+ mcdb->debug[idx].op, b->entries[idx].result, mcdb->caller[idx]);
+ if (mcdb->argsz[idx]) {
+ pr_cont(" args=");
+ for (arg = 0; arg < mcdb->argsz[idx] / 8; arg++)
+ pr_cont("%lx ", mcdb->debug[idx].args[arg]);
+ }
+ pr_cont("\n");
+}
+
+static struct mc_debug_data * __ref get_mc_debug_ptr(void)
+{
+ if (likely(mc_debug_data))
+ return this_cpu_ptr(mc_debug_data);
+
+ return &mc_debug_data_early;
+}
+
void xen_mc_flush(void)
{
struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
struct multicall_entry *mc;
+ struct mc_debug_data *mcdb = NULL;
int ret = 0;
unsigned long flags;
int i;
@@ -69,10 +136,11 @@ void xen_mc_flush(void)
trace_xen_mc_flush(b->mcidx, b->argidx, b->cbidx);
-#if MC_DEBUG
- memcpy(b->debug, b->entries,
- b->mcidx * sizeof(struct multicall_entry));
-#endif
+ if (static_key_false(&mc_debug)) {
+ mcdb = get_mc_debug_ptr();
+ memcpy(mcdb->debug, b->entries,
+ b->mcidx * sizeof(struct multicall_entry));
+ }
switch (b->mcidx) {
case 0:
@@ -104,20 +172,15 @@ void xen_mc_flush(void)
ret, b->mcidx, smp_processor_id());
for (i = 0; i < b->mcidx; i++) {
if (b->entries[i].result < 0) {
-#if MC_DEBUG
- pr_err(" call %2d: op=%lu arg=[%lx] result=%ld\t%pS\n",
- i + 1,
- b->debug[i].op,
- b->debug[i].args[0],
- b->entries[i].result,
- b->caller[i]);
-#else
- pr_err(" call %2d: op=%lu arg=[%lx] result=%ld\n",
- i + 1,
- b->entries[i].op,
- b->entries[i].args[0],
- b->entries[i].result);
-#endif
+ if (static_key_false(&mc_debug)) {
+ print_debug_data(b, mcdb, i);
+ } else {
+ pr_err(" call %2d: op=%lu arg=[%lx] result=%ld\n",
+ i + 1,
+ b->entries[i].op,
+ b->entries[i].args[0],
+ b->entries[i].result);
+ }
}
}
}
@@ -155,9 +218,12 @@ struct multicall_space __xen_mc_entry(size_t args)
}
ret.mc = &b->entries[b->mcidx];
-#if MC_DEBUG
- b->caller[b->mcidx] = __builtin_return_address(0);
-#endif
+ if (static_key_false(&mc_debug)) {
+ struct mc_debug_data *mcdb = get_mc_debug_ptr();
+
+ mcdb->caller[b->mcidx] = __builtin_return_address(0);
+ mcdb->argsz[b->mcidx] = args;
+ }
b->mcidx++;
ret.args = &b->args[argidx];
b->argidx = argidx + args;
--
2.35.3
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