fix CPER issues related to UEFI 2.9A Errata

The UEFI 2.9A errata makes clear how ARM processor type encoding should be done: it is meant to be equal to Generic processor, using a bitmask.

The current code assumes, for both generic and ARM processor types that this is an integer, which is an incorrect assumption.

Fix it. While here, also fix a compilation issue when using W=1.

After the change, Kernel will properly decode receiving two errors at the same message, as defined at UEFI spec:

[   75.282430] Memory failure: 0x5cdfd: recovery action for free buddy page: Recovered
[   94.973081] {2}[Hardware Error]: Hardware error from APEI Generic Hardware Error Source: 1
[   94.973770] {2}[Hardware Error]: event severity: recoverable
[   94.974334] {2}[Hardware Error]:  Error 0, type: recoverable
[   94.974962] {2}[Hardware Error]:   section_type: ARM processor error
[   94.975586] {2}[Hardware Error]:   MIDR: 0x000000000000cd24
[   94.976202] {2}[Hardware Error]:   Multiprocessor Affinity Register (MPIDR): 0x000000000000ab12
[   94.977011] {2}[Hardware Error]:   error affinity level: 2
[   94.977593] {2}[Hardware Error]:   running state: 0x1
[   94.978135] {2}[Hardware Error]:   Power State Coordination Interface state: 4660
[   94.978884] {2}[Hardware Error]:   Error info structure 0:
[   94.979463] {2}[Hardware Error]:   num errors: 3
[   94.979971] {2}[Hardware Error]:    first error captured
[   94.980523] {2}[Hardware Error]:    propagated error captured
[   94.981110] {2}[Hardware Error]:    overflow occurred, error info is incomplete
[   94.981893] {2}[Hardware Error]:    error_type: 0x0006: cache error|TLB error
[   94.982606] {2}[Hardware Error]:    error_info: 0x000000000091000f
[   94.983249] {2}[Hardware Error]:     transaction type: Data Access
[   94.983891] {2}[Hardware Error]:     cache error, operation type: Data write
[   94.984559] {2}[Hardware Error]:     TLB error, operation type: Data write
[   94.985215] {2}[Hardware Error]:     cache level: 2
[   94.985749] {2}[Hardware Error]:     TLB level: 2
[   94.986277] {2}[Hardware Error]:     processor context not corrupted

And the error code is properly decoded according with table N.17 from UEFI 2.10 spec:

	[   94.981893] {2}[Hardware Error]:    error_type: 0x0006: cache error|TLB error

The error injection logic was checked via QEMU using this patch:
https://lore.kernel.org/all/[email protected]/

v5:
- Do some cleanups and minor fixes as suggested by Jonathan and Tony:
- check errors at strscpy();
- simplify cper_bits_to_str() function;
- use FIELD_GET() and for_each_set_bit();
- use ARRAY_SIZE() on infofx to let it clear that it should be size of newpfx + 1;
- fix kernel-doc warning with W=1;
- use kernel-doc for two exported functions at cper.c.

v4:
- The print function had some bugs on it, which was discovered with the help of an error injection tool I'm now using.

v3:
- It adds a helper function to produce a buffer describing the error bits at cper's printk and ghes pr_warn_bitrated. It also fixes a W=1 error while building cper.

v2:
- It fixes the way printks are handled on both cper_arm and ghes drivers.

v1:
- (tagged as RFC) was mostly to give a heads up that the current implementation is not following the spec. It also touches only cper code.

Mauro Carvalho Chehab (4):
efi/cper: Adjust infopfx size to accept an extra space efi/cper: Add a new helper function to print bitmasks efi/cper: align ARM CPER type with UEFI 2.9A/2.10 specs
docs: efi: add CPER functions to driver-api

 .../driver-api/firmware/efi/index.rst         | 11 ++--
 drivers/acpi/apei/ghes.c                      | 15 +++---
 drivers/firmware/efi/cper-arm.c               | 52 +++++++++----------
 drivers/firmware/efi/cper.c                   | 41 ++++++++++++++-
 include/linux/cper.h                          | 12 +++--
 5 files changed, 89 insertions(+), 42 deletions(-)

2.45.2

Compiling with W=1 with werror enabled produces an error:

drivers/firmware/efi/cper-arm.c: In function ‘cper_print_proc_arm’:
drivers/firmware/efi/cper-arm.c:298:64: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
298 | snprintf(infopfx, sizeof(infopfx), "%s ", newpfx);
| ^
drivers/firmware/efi/cper-arm.c:298:25: note: ‘snprintf’ output between 2 and 65 bytes into a destination of size 64

  298 |                         snprintf(infopfx, sizeof(infopfx), "%s ", newpfx);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As the logic there adds an space at the end of infopx buffer. Add an extra space to avoid such warning.

---
 drivers/firmware/efi/cper-arm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index fa9c1c3bf168..eb7ee6af55f2 100644
@@ -240,7 +240,7 @@ void cper_print_proc_arm(const char *pfx,
 	int i, len, max_ctx_type;
 	struct cper_arm_err_info *err_info;
 	struct cper_arm_ctx_info *ctx_info;
-	char newpfx[64], infopfx[64];
+	char newpfx[64], infopfx[ARRAY_SIZE(newpfx) + 1];
 
 	printk("%sMIDR: 0x%016llx\n", pfx, proc->midr);
 

2.45.2

Sometimes it is desired to produce a single log line for errors. Add a new helper function for such purpose.

---
 drivers/firmware/efi/cper.c | 41 +++++++++++++++++++++++++++++++++++++
 include/linux/cper.h        |  2 ++
 2 files changed, 43 insertions(+)

index 7d2cdd9e2227..4cf56657afde 100644
@@ -106,6 +106,47 @@ void cper_print_bits(const char *pfx, unsigned int bits,
 		printk("%s\n", buf);
 }
 
+/*
+ * cper_bits_to_str - return a string for set bits
+ * @buf: buffer to store the output string
+ * @buf_size: size of the output string buffer
+ * @bits: bit mask
+ * @strs: string array, indexed by bit position
+ * @strs_size: size of the string array: @strs
+ * @mask: a continuous bitmask used to detect the first valid bit of the
+ *        bitmap.
+ *
+ * Add to @buf the bitmask in hexadecimal. Then, for each set bit in @bits
+ * mask, add the corresponding string describing the bit in @strs to @buf.
+ */
+char *cper_bits_to_str(char *buf, int buf_size, unsigned long bits,
+		       const char * const strs[], unsigned int strs_size)
+{
+	int len = buf_size;
+	char *str = buf;
+	int i, size;
+
+	for_each_set_bit(i, &bits, strs_size) {
+		if (!(bits & (1U << (i))))
+			continue;
+
+		if (*buf && len > 0) {
+			*str = '|';
+			len--;
+			str++;
+		}
+
+		size = strscpy(str, strs[i], len);
+		if (size < 0)
+			break;
+
+		len -= size;
+		str += size;
+	}
+	return buf;
+}
+EXPORT_SYMBOL_GPL(cper_bits_to_str);
+
 static const char * const proc_type_strs[] = {
 	"IA32/X64",
 	"IA64",

index 265b0f8fc0b3..c2f14b916bfb 100644
@@ -584,6 +584,8 @@ const char *cper_mem_err_type_str(unsigned int);
 const char *cper_mem_err_status_str(u64 status);
 void cper_print_bits(const char *prefix, unsigned int bits,
 		     const char * const strs[], unsigned int strs_size);
+char *cper_bits_to_str(char *buf, int buf_size, unsigned long bits,
+		       const char * const strs[], unsigned int strs_size);
 void cper_mem_err_pack(const struct cper_sec_mem_err *,
 		       struct cper_mem_err_compact *);
 const char *cper_mem_err_unpack(struct trace_seq *,

2.45.2

This description is a bit cryptic. Maybe an example would make it easier for anyone coming across this in the future?

Minor comment inline.

	bool first = true;
...
		if (!first && len > 0) {
			*str = '|';
			len--;
			str++;
		}
		first = false;

Up to UEFI spec, the type byte of CPER struct for ARM processor was defined simply as:

Type at byte offset 4:

- Cache error
- TLB Error
- Bus Error
- Micro-architectural Error
All other values are reserved

Yet, there was no information about how this would be encoded.

Spec 2.9A errata corrected it by defining:

- Bit 1 - Cache Error
- Bit 2 - TLB Error
- Bit 3 - Bus Error
- Bit 4 - Micro-architectural Error
All other values are reserved

That actually aligns with the values already defined on older versions at N.2.4.1. Generic Processor Error Section.

Spec 2.10 also preserve the same encoding as 2.9A

Adjust CPER and GHES handling code for both generic and ARM processors to properly handle UEFI 2.9A and 2.10 encoding.

---
 drivers/acpi/apei/ghes.c        | 15 ++++++----
 drivers/firmware/efi/cper-arm.c | 50 ++++++++++++++++-----------------
 include/linux/cper.h            | 10 +++----
 3 files changed, 38 insertions(+), 37 deletions(-)

index 623cc0cb4a65..de79cc0a0f1d 100644
@@ -533,6 +533,7 @@ static bool ghes_handle_arm_hw_error(struct acpi_hest_generic_data *gdata,
 {
 	struct cper_sec_proc_arm *err = acpi_hest_get_payload(gdata);
 	int flags = sync ? MF_ACTION_REQUIRED : 0;
+	char error_type[120];
 	bool queued = false;
 	int sec_sev, i;
 	char *p;

@@ -546,9 +547,8 @@ static bool ghes_handle_arm_hw_error(struct acpi_hest_generic_data *gdata,
 	p = (char *)(err + 1);
 	for (i = 0; i < err->err_info_num; i++) {
 		struct cper_arm_err_info *err_info = (struct cper_arm_err_info *)p;
-		bool is_cache = (err_info->type == CPER_ARM_CACHE_ERROR);
+		bool is_cache = err_info->type & CPER_ARM_CACHE_ERROR;
 		bool has_pa = (err_info->validation_bits & CPER_ARM_INFO_VALID_PHYSICAL_ADDR);
-		const char *error_type = "unknown error";
 
 		/*
 		 * The field (err_info->error_info & BIT(26)) is fixed to set to

@@ -562,12 +562,15 @@ static bool ghes_handle_arm_hw_error(struct acpi_hest_generic_data *gdata,
 			continue;
 		}
 
-		if (err_info->type < ARRAY_SIZE(cper_proc_error_type_strs))
-			error_type = cper_proc_error_type_strs[err_info->type];
+		cper_bits_to_str(error_type, sizeof(error_type),
+				 FIELD_GET(CPER_ARM_ERR_TYPE_MASK, err_info->type),
+				 cper_proc_error_type_strs,
+				 ARRAY_SIZE(cper_proc_error_type_strs));
 
 		pr_warn_ratelimited(FW_WARN GHES_PFX
-				    "Unhandled processor error type: %s\n",
-				    error_type);
+				    "Unhandled processor error type 0x%02x: %s%s\n",
+				    err_info->type, error_type,
+				    (err_info->type & ~CPER_ARM_ERR_TYPE_MASK) ? " with reserved bit(s)" : "");
 		p += err_info->length;
 	}
 

index c2f14b916bfb..fc62a80575e8 100644
@@ -293,11 +293,11 @@ enum {
 #define CPER_ARM_INFO_FLAGS_PROPAGATED		BIT(2)
 #define CPER_ARM_INFO_FLAGS_OVERFLOW		BIT(3)
 
-#define CPER_ARM_CACHE_ERROR			0
-#define CPER_ARM_TLB_ERROR			1
-#define CPER_ARM_BUS_ERROR			2
-#define CPER_ARM_VENDOR_ERROR			3
-#define CPER_ARM_MAX_TYPE			CPER_ARM_VENDOR_ERROR
+#define CPER_ARM_ERR_TYPE_MASK			GENMASK(4,1)
+#define CPER_ARM_CACHE_ERROR			BIT(1)
+#define CPER_ARM_TLB_ERROR			BIT(2)
+#define CPER_ARM_BUS_ERROR			BIT(3)
+#define CPER_ARM_VENDOR_ERROR			BIT(4)
 
 #define CPER_ARM_ERR_VALID_TRANSACTION_TYPE	BIT(0)
 #define CPER_ARM_ERR_VALID_OPERATION_TYPE	BIT(1)

2.45.2

There are two kernel-doc like descriptions at cper, which is used by other parts of cper and on ghes driver. They both have kernel-doc like descriptions.

Change the tags for them to be actual kernel-doc tags and add them to the driver-api documentaion at the UEFI section.

---
 Documentation/driver-api/firmware/efi/index.rst | 11 ++++++++---
 drivers/firmware/efi/cper.c                     | 10 ++++------
 2 files changed, 12 insertions(+), 9 deletions(-)

index 4fe8abba9fc6..5a6b6229592c 100644
@@ -1,11 +1,16 @@
 .. SPDX-License-Identifier: GPL-2.0
 
-============
-UEFI Support
-============
+====================================================
+Unified Extensible Firmware Interface (UEFI) Support
+====================================================
 
 UEFI stub library functions
 ===========================
 
 .. kernel-doc:: drivers/firmware/efi/libstub/mem.c
    :internal:
+
+UEFI Common Platform Error Record (CPER) functions
+==================================================
+
+.. kernel-doc:: drivers/firmware/efi/cper.c

index 4cf56657afde..c8a432c5cb5d 100644
@@ -69,7 +69,7 @@ const char *cper_severity_str(unsigned int severity)
 }
 EXPORT_SYMBOL_GPL(cper_severity_str);
 
-/*
+/**
  * cper_print_bits - print strings for set bits
  * @pfx: prefix for each line, including log level and prefix string
  * @bits: bit mask

@@ -106,18 +106,16 @@ void cper_print_bits(const char *pfx, unsigned int bits,
 		printk("%s\n", buf);
 }
 
-/*
+/**
  * cper_bits_to_str - return a string for set bits
  * @buf: buffer to store the output string
  * @buf_size: size of the output string buffer
  * @bits: bit mask
  * @strs: string array, indexed by bit position
  * @strs_size: size of the string array: @strs
- * @mask: a continuous bitmask used to detect the first valid bit of the
- *        bitmap.
  *
- * Add to @buf the bitmask in hexadecimal. Then, for each set bit in @bits
- * mask, add the corresponding string describing the bit in @strs to @buf.
+ * Add to @buf the bitmask in hexadecimal. Then, for each set bit in @bits,
+ * add the corresponding string describing the bit in @strs to @buf.
  */
 char *cper_bits_to_str(char *buf, int buf_size, unsigned long bits,
 		       const char * const strs[], unsigned int strs_size)

2.45.2