diff mbox series

[v5,5/5] x86/CPU/AMD: Print the reason for the last reset

Message ID 20250422234830.2840784-6-superm1@kernel.org
State New
Headers show
Series AMD Zen debugging documentation | expand

Commit Message

Mario Limonciello April 22, 2025, 11:48 p.m. UTC 
From: Yazen Ghannam <yazen.ghannam@amd.com>

The following register contains bits that indicate the cause for the
previous reset.

        PMx000000C0 (FCH::PM::S5_RESET_STATUS)

This is useful for debug. The reasons for reset are broken into 6 high
level categories. Decode it by category and print during boot.

Specifics within a category are split off into debugging documentation.

The register is accessed indirectly through a "PM" port in the FCH. Use
MMIO access in order to avoid restrictions with legacy port access.

Use a late_initcall() to ensure that MMIO has been set up before trying
to access the register.

This register was introduced with AMD Family 17h, so avoid access on
older families. There is no CPUID feature bit for this register.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Co-developed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
v4:
 * Use loop that can output multiple reasons
 * Drop "Unknown" condition and have dedicated message
v3:
 * Align strings in the CSV and code.
 * Switch to an array of strings
 * Switch to looking up bit of first value
 * Re-order message to have number first (makes grepping easier)
 * Add x86/amd prefix to message
v2:
 * Add string for each reason, but still include value in case multiple
   values are set.
---
 Documentation/arch/x86/amd-debugging.rst | 41 +++++++++++++++
 arch/x86/include/asm/amd/fch.h           |  1 +
 arch/x86/kernel/cpu/amd.c                | 64 ++++++++++++++++++++++++
 3 files changed, 106 insertions(+)

Comments

Borislav Petkov April 30, 2025, 7:03 p.m. UTC | #1 
On Tue, Apr 22, 2025 at 06:48:30PM -0500, Mario Limonciello wrote:
> +	/* Iterate on each bit in the 'value' mask: */
> +	while (true) {
> +		bit = find_next_bit(&value, BITS_PER_LONG, bit + 1);
> +
> +		/* Reached the end of the word, no more bits: */
> +		if (bit >= BITS_PER_LONG) {
> +			if (!nr_reasons)
> +				pr_info("x86/amd: Previous system reset reason [0x%08lx]: Unknown\n", value);
> +			break;
> +		}
> +
> +		if (!s5_reset_reason_txt[bit])
> +			continue;
> +
> +		nr_reasons++;
> +		pr_info("x86/amd: Previous system reset reason [0x%08lx]: %s\n",
> +			value, s5_reset_reason_txt[bit]);
> +	}

What happened to that simpler idea:

https://lore.kernel.org/r/20250411125050.GEZ_kQKtYBfEMDQuXU@fat_crate.local

?
Mario Limonciello April 30, 2025, 7:05 p.m. UTC | #2 
On 4/30/2025 2:03 PM, Borislav Petkov wrote:
> On Tue, Apr 22, 2025 at 06:48:30PM -0500, Mario Limonciello wrote:
>> +	/* Iterate on each bit in the 'value' mask: */
>> +	while (true) {
>> +		bit = find_next_bit(&value, BITS_PER_LONG, bit + 1);
>> +
>> +		/* Reached the end of the word, no more bits: */
>> +		if (bit >= BITS_PER_LONG) {
>> +			if (!nr_reasons)
>> +				pr_info("x86/amd: Previous system reset reason [0x%08lx]: Unknown\n", value);
>> +			break;
>> +		}
>> +
>> +		if (!s5_reset_reason_txt[bit])
>> +			continue;
>> +
>> +		nr_reasons++;
>> +		pr_info("x86/amd: Previous system reset reason [0x%08lx]: %s\n",
>> +			value, s5_reset_reason_txt[bit]);
>> +	}
> 
> What happened to that simpler idea:
> 
> https://lore.kernel.org/r/20250411125050.GEZ_kQKtYBfEMDQuXU@fat_crate.local
> 

This one was more advantageous in that if multiple bits were set for any 
reason we could get messages for all of them printed.
Borislav Petkov April 30, 2025, 7:10 p.m. UTC | #3 
On Wed, Apr 30, 2025 at 02:05:44PM -0500, Mario Limonciello wrote:
> On 4/30/2025 2:03 PM, Borislav Petkov wrote:
> > On Tue, Apr 22, 2025 at 06:48:30PM -0500, Mario Limonciello wrote:
> > > +	/* Iterate on each bit in the 'value' mask: */
> > > +	while (true) {
> > > +		bit = find_next_bit(&value, BITS_PER_LONG, bit + 1);
> > > +
> > > +		/* Reached the end of the word, no more bits: */
> > > +		if (bit >= BITS_PER_LONG) {
> > > +			if (!nr_reasons)
> > > +				pr_info("x86/amd: Previous system reset reason [0x%08lx]: Unknown\n", value);
> > > +			break;
> > > +		}
> > > +
> > > +		if (!s5_reset_reason_txt[bit])
> > > +			continue;
> > > +
> > > +		nr_reasons++;
> > > +		pr_info("x86/amd: Previous system reset reason [0x%08lx]: %s\n",
> > > +			value, s5_reset_reason_txt[bit]);
> > > +	}
> > 
> > What happened to that simpler idea:
> > 
> > https://lore.kernel.org/r/20250411125050.GEZ_kQKtYBfEMDQuXU@fat_crate.local
> > 
> 
> This one was more advantageous in that if multiple bits were set for any
> reason we could get messages for all of them printed.

I don't understand - you dump an array element for every bit now too...
Mario Limonciello April 30, 2025, 7:17 p.m. UTC | #4 
On 4/30/2025 2:10 PM, Borislav Petkov wrote:
> On Wed, Apr 30, 2025 at 02:05:44PM -0500, Mario Limonciello wrote:
>> On 4/30/2025 2:03 PM, Borislav Petkov wrote:
>>> On Tue, Apr 22, 2025 at 06:48:30PM -0500, Mario Limonciello wrote:
>>>> +	/* Iterate on each bit in the 'value' mask: */
>>>> +	while (true) {
>>>> +		bit = find_next_bit(&value, BITS_PER_LONG, bit + 1);
>>>> +
>>>> +		/* Reached the end of the word, no more bits: */
>>>> +		if (bit >= BITS_PER_LONG) {
>>>> +			if (!nr_reasons)
>>>> +				pr_info("x86/amd: Previous system reset reason [0x%08lx]: Unknown\n", value);
>>>> +			break;
>>>> +		}
>>>> +
>>>> +		if (!s5_reset_reason_txt[bit])
>>>> +			continue;
>>>> +
>>>> +		nr_reasons++;
>>>> +		pr_info("x86/amd: Previous system reset reason [0x%08lx]: %s\n",
>>>> +			value, s5_reset_reason_txt[bit]);
>>>> +	}
>>>
>>> What happened to that simpler idea:
>>>
>>> https://lore.kernel.org/r/20250411125050.GEZ_kQKtYBfEMDQuXU@fat_crate.local
>>>
>>
>> This one was more advantageous in that if multiple bits were set for any
>> reason we could get messages for all of them printed.
> 
> I don't understand - you dump an array element for every bit now too...
> 

Well with that approach once you got a known bit set you broke the loop 
and would print a message for that known bit.  But if you have two bits 
set you either need another loop or you only get one message print.
Borislav Petkov April 30, 2025, 7:25 p.m. UTC | #5 
On Wed, Apr 30, 2025 at 02:17:43PM -0500, Mario Limonciello wrote:
> Well with that approach once you got a known bit set you broke the loop and
> would print a message for that known bit.  But if you have two bits set you
> either need another loop or you only get one message print.

So I gather you want to print for *each* set bit?

If so:

	for (i = 0; i <= ARRAY_SIZE(s5_reset_reason_txt); i++) {
		if (!(value & BIT(i)))
			continue;

		if (s5_reset_reason_txt[i])
			pr_info(...);
	}

Still a lot easier instead of calling some function and dealing with from
which bit to start etc etc.
Mario Limonciello April 30, 2025, 7:32 p.m. UTC | #6 
On 4/30/2025 2:25 PM, Borislav Petkov wrote:
> On Wed, Apr 30, 2025 at 02:17:43PM -0500, Mario Limonciello wrote:
>> Well with that approach once you got a known bit set you broke the loop and
>> would print a message for that known bit.  But if you have two bits set you
>> either need another loop or you only get one message print.
> 
> So I gather you want to print for *each* set bit?
> 
> If so:
> 
> 	for (i = 0; i <= ARRAY_SIZE(s5_reset_reason_txt); i++) {
> 		if (!(value & BIT(i)))
> 			continue;
> 
> 		if (s5_reset_reason_txt[i])
> 			pr_info(...);
> 	}
> 
> Still a lot easier instead of calling some function and dealing with from
> which bit to start etc etc.
> 
> 

This would work, but would still need to track if "no" known bits were 
set to emit an "unknown" message.

So the loops end up being for() and check a bit or while (true) and 
find_next_bit() and otherwise identical.

At that point does it really buy much more than the while (true) 
approach and find_next_bit()?
Borislav Petkov April 30, 2025, 7:38 p.m. UTC | #7 
On Wed, Apr 30, 2025 at 02:32:44PM -0500, Mario Limonciello wrote:
> This would work, but would still need to track if "no" known bits were set
> to emit an "unknown" message.
> 
> So the loops end up being for() and check a bit or while (true) and
> find_next_bit() and otherwise identical.
> 
> At that point does it really buy much more than the while (true) approach
> and find_next_bit()?

I have the requirements now, thanks. Lemme hack it up tomorrow, on a clear
head.

Thx.
Borislav Petkov May 1, 2025, 8:31 a.m. UTC | #8 
On Wed, Apr 30, 2025 at 02:32:44PM -0500, Mario Limonciello wrote:
> This would work, but would still need to track if "no" known bits were set
> to emit an "unknown" message.

No, when no bits are set, you don't emit anything. Because the information
content of "oh, your system rebooted due to an unknown reason" is minimal and
even actively confusing at best.

Let sleeping dogs lie.

---
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index bef871adbf84..9a8c590456d0 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1264,10 +1264,9 @@ static const char * const s5_reset_reason_txt[] = {
 
 static __init int print_s5_reset_status_mmio(void)
 {
-	void __iomem *addr;
 	unsigned long value;
-	int nr_reasons = 0;
-	int bit = -1;
+	void __iomem *addr;
+	int i;
 
 	if (!cpu_feature_enabled(X86_FEATURE_ZEN))
 		return 0;
@@ -1279,23 +1278,13 @@ static __init int print_s5_reset_status_mmio(void)
 	value = ioread32(addr);
 	iounmap(addr);
 
-	/* Iterate on each bit in the 'value' mask: */
-	while (true) {
-		bit = find_next_bit(&value, BITS_PER_LONG, bit + 1);
-
-		/* Reached the end of the word, no more bits: */
-		if (bit >= BITS_PER_LONG) {
-			if (!nr_reasons)
-				pr_info("x86/amd: Previous system reset reason [0x%08lx]: Unknown\n", value);
-			break;
-		}
-
-		if (!s5_reset_reason_txt[bit])
+	for (i = 0; i <= ARRAY_SIZE(s5_reset_reason_txt); i++) {
+		if (!(value & BIT(i)))
 			continue;
 
-		nr_reasons++;
-		pr_info("x86/amd: Previous system reset reason [0x%08lx]: %s\n",
-			value, s5_reset_reason_txt[bit]);
+		if (s5_reset_reason_txt[i])
+			pr_info("x86/amd: Previous system reset reason [0x%08lx]: %s\n",
+				value, s5_reset_reason_txt[i]);
 	}
 
 	return 0;
Ingo Molnar May 4, 2025, 6:38 a.m. UTC | #9 
* Borislav Petkov <bp@alien8.de> wrote:

> +	for (i = 0; i <= ARRAY_SIZE(s5_reset_reason_txt); i++) {
> +		if (!(value & BIT(i)))
>  			continue;
>  
> -		nr_reasons++;
> -		pr_info("x86/amd: Previous system reset reason [0x%08lx]: %s\n",
> -			value, s5_reset_reason_txt[bit]);
> +		if (s5_reset_reason_txt[i])
> +			pr_info("x86/amd: Previous system reset reason [0x%08lx]: %s\n",
> +				value, s5_reset_reason_txt[i]);
>  	}

Yeah, this is much more straightforward code that gets us all the 
information - as diagnostics code should be.

Thanks,

	Ingo
diff mbox series

Patch

diff --git a/Documentation/arch/x86/amd-debugging.rst b/Documentation/arch/x86/amd-debugging.rst
index 01427cf97ee33..32a3f99409c7a 100644
--- a/Documentation/arch/x86/amd-debugging.rst
+++ b/Documentation/arch/x86/amd-debugging.rst
@@ -319,3 +319,44 @@  messages.  To help with this, a tool has been created at
 `amd-debug-tools <https://git.kernel.org/pub/scm/linux/kernel/git/superm1/amd-debug-tools.git/about/>`_
 to help parse the messages.
 
+Random reboot issues
+====================
+When a random reboot occurs, the high-level reason for the reboot is stored
+in a register that will persist onto the next boot.
+
+There are 6 classes of reasons for the reboot:
+ * Software induced
+ * Power state transition
+ * Pin induced
+ * Hardware induced
+ * Remote reset
+ * Internal CPU event
+
+.. csv-table::
+   :header: "Bit", "Type", "Reason"
+   :align: left
+
+   "0",  "Pin",      "thermal pin BP_THERMTRIP_L was tripped"
+   "1",  "Pin",      "power button was pressed for 4 seconds"
+   "2",  "Pin",      "shutdown pin was shorted"
+   "4",  "Remote",   "remote ASF power off command was received"
+   "9",  "Internal", "internal CPU thermal limit was tripped"
+   "16", "Pin",      "system reset pin BP_SYS_RST_L was tripped"
+   "17", "Software", "software issued PCI reset"
+   "18", "Software", "software wrote 0x4 to reset control register 0xCF9"
+   "19", "Software", "software wrote 0x6 to reset control register 0xCF9"
+   "20", "Software", "software wrote 0xE to reset control register 0xCF9"
+   "21", "Sleep",    "ACPI power state transition occurred"
+   "22", "Pin",      "keyboard reset pin KB_RST_L was asserted"
+   "23", "Internal", "internal CPU shutdown event occurred"
+   "24", "Hardware", "system failed to boot before failed boot timer expired"
+   "25", "Hardware", "hardware watchdog timer expired"
+   "26", "Remote",   "remote ASF reset command was received"
+   "27", "Internal", "an uncorrected error caused a data fabric sync flood event"
+   "29", "Internal", "FCH and MP1 failed warm reset handshake"
+   "30", "Internal", "a parity error occurred"
+   "31", "Internal", "a software sync flood event occurred"
+
+This information is read by the kernel at bootup and is saved into the
+kernel ring buffer. When a random reboot occurs this message can be helpful
+to determine the next component to debug such an issue.
diff --git a/arch/x86/include/asm/amd/fch.h b/arch/x86/include/asm/amd/fch.h
index 9b32e8a03193e..4a6e1e3b685a4 100644
--- a/arch/x86/include/asm/amd/fch.h
+++ b/arch/x86/include/asm/amd/fch.h
@@ -9,5 +9,6 @@ 
 #define FCH_PM_DECODEEN			0x00
 #define FCH_PM_DECODEEN_SMBUS0SEL	GENMASK(20, 19)
 #define FCH_PM_SCRATCH			0x80
+#define FCH_PM_S5_RESET_STATUS		0xC0
 
 #endif
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 1f7925e45b46d..aed82b9ccf8ce 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -9,6 +9,7 @@ 
 #include <linux/sched/clock.h>
 #include <linux/random.h>
 #include <linux/topology.h>
+#include <asm/amd/fch.h>
 #include <asm/processor.h>
 #include <asm/apic.h>
 #include <asm/cacheinfo.h>
@@ -1237,3 +1238,66 @@  void amd_check_microcode(void)
 	if (cpu_feature_enabled(X86_FEATURE_ZEN2))
 		on_each_cpu(zenbleed_check_cpu, NULL, 1);
 }
+
+static const char * const s5_reset_reason_txt[] = {
+	[0] = "thermal pin BP_THERMTRIP_L was tripped",
+	[1] = "power button was pressed for 4 seconds",
+	[2] = "shutdown pin was shorted",
+	[4] = "remote ASF power off command was received",
+	[9] = "internal CPU thermal limit was tripped",
+	[16] = "system reset pin BP_SYS_RST_L was tripped",
+	[17] = "software issued PCI reset",
+	[18] = "software wrote 0x4 to reset control register 0xCF9",
+	[19] = "software wrote 0x6 to reset control register 0xCF9",
+	[20] = "software wrote 0xE to reset control register 0xCF9",
+	[21] = "ACPI power state transition occurred",
+	[22] = "keyboard reset pin KB_RST_L was asserted",
+	[23] = "internal CPU shutdown event occurred",
+	[24] = "system failed to boot before failed boot timer expired",
+	[25] = "hardware watchdog timer expired",
+	[26] = "remote ASF reset command was received",
+	[27] = "an uncorrected error caused a data fabric sync flood event",
+	[29] = "FCH and MP1 failed warm reset handshake",
+	[30] = "a parity error occurred",
+	[31] = "a software sync flood event occurred",
+};
+
+static __init int print_s5_reset_status_mmio(void)
+{
+	void __iomem *addr;
+	unsigned long value;
+	int nr_reasons = 0;
+	int bit = -1;
+
+	if (!cpu_feature_enabled(X86_FEATURE_ZEN))
+		return 0;
+
+	addr = ioremap(FCH_PM_BASE + FCH_PM_S5_RESET_STATUS, sizeof(value));
+	if (!addr)
+		return 0;
+
+	value = ioread32(addr);
+	iounmap(addr);
+
+	/* Iterate on each bit in the 'value' mask: */
+	while (true) {
+		bit = find_next_bit(&value, BITS_PER_LONG, bit + 1);
+
+		/* Reached the end of the word, no more bits: */
+		if (bit >= BITS_PER_LONG) {
+			if (!nr_reasons)
+				pr_info("x86/amd: Previous system reset reason [0x%08lx]: Unknown\n", value);
+			break;
+		}
+
+		if (!s5_reset_reason_txt[bit])
+			continue;
+
+		nr_reasons++;
+		pr_info("x86/amd: Previous system reset reason [0x%08lx]: %s\n",
+			value, s5_reset_reason_txt[bit]);
+	}
+
+	return 0;
+}
+late_initcall(print_s5_reset_status_mmio);