[PATCH v7 0/3] powerpc/fadump: Improvements for firmware-assisted dump.

[PATCH v7 0/3] powerpc/fadump: Improvements for firmware-assisted dump.

[Mahesh J Salgaonkar]

One of the primary issues with Firmware Assisted Dump (fadump) on Power
is that it needs a large amount of memory to be reserved. This reserved
memory is used for saving the contents of old crashed kernel's memory before
fadump capture kernel uses old kernel's memory area to boot. However, This
reserved memory area stays unused until system crash and isn't available
for production kernel to use.

Instead of setting aside a significant chunk of memory that nobody can use,
take advantage Linux kernel's Contiguous Memory Allocator (CMA) feature,
to reserve a significant chunk of memory that the kernel is prevented from
using, but applications are free to use it.

Patch 1 implements the usage of CMA region to allow production kernel to
use that memory for applications usage, making fadump reservationless.
We now initialize siginificant chunk of faump reserved memory for CMA.

Cahnges in V7:
- Revert back to use CMA for fadump reservation.
- Add fadump=nocma option to fall back default behaviour.

Changes in V6:
- Introduce an interface to mark reserved memory as ZONE_MOVABLE. Hence
  sending this series as RFC again.
- Mark reserved area as ZONE_MOVABLE instead of CMA.
- Add fadump=nonmovable parameter for user who don't want to use ZONE_MOVABLE.

Changes in V5:
- Drop the patch that does metadata movement.
- Move the kexec fix patch to top (patch 1)
- Fold CMA documenation patch into patch 2
- Fix the compilation issues when CONFIG_CMA is not set reported by Hari.
- Use the approach of using boot memory size for CMA as suggested by Hari
  except the movement of sections. Thanks to Hari.

Changes in V4:
- patch 1: Make fadump compatible irrespective of kernel versions.
- patch 4: moved out of the series and been posted seperatly at
  http://patchwork.ozlabs.org/patch/896716/
- Documentation update about CMA reservation.

Changes in V3:
- patch 1 & 2: move metadata region and documentation update.
- patch 7: Un-register the faudmp on kexec path


---

Mahesh Salgaonkar (3):
      powerpc/fadump: Reservationless firmware assisted dump
      powerpc/fadump: throw proper error message on fadump registration failure.
      powerpc/fadump: Do not allow hot-remove memory from fadump reserved area.


 Documentation/powerpc/firmware-assisted-dump.txt |   17 +++
 arch/powerpc/include/asm/fadump.h                |    7 +
 arch/powerpc/kernel/fadump.c                     |  140 ++++++++++++++++++++--
 arch/powerpc/platforms/pseries/hotplug-memory.c  |    7 +
 4 files changed, 155 insertions(+), 16 deletions(-)

--
Signature

[PATCH v7 1/3] powerpc/fadump: Reservationless firmware assisted dump

[Mahesh J Salgaonkar]

From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>

One of the primary issues with Firmware Assisted Dump (fadump) on Power
is that it needs a large amount of memory to be reserved. On large
systems with TeraBytes of memory, this reservation can be quite
significant.

In some cases, fadump fails if the memory reserved is insufficient, or
if the reserved memory was DLPAR hot-removed.

In the normal case, post reboot, the preserved memory is filtered to
extract only relevant areas of interest using the makedumpfile tool.
While the tool provides flexibility to determine what needs to be part
of the dump and what memory to filter out, all supported distributions
default this to "Capture only kernel data and nothing else".

We take advantage of this default and the Linux kernel's Contiguous
Memory Allocator (CMA) to fundamentally change the memory reservation
model for fadump.

Instead of setting aside a significant chunk of memory nobody can use,
this patch uses CMA instead, to reserve a significant chunk of memory
that the kernel is prevented from using (due to MIGRATE_CMA), but
applications are free to use it. With this fadump will still be able
to capture all of the kernel memory and most of the user space memory
except the user pages that were present in CMA region.

Essentially, on a P9 LPAR with 2 cores, 8GB RAM and current upstream:
[root@zzxx-yy10 ~]# free -m
              total        used        free      shared  buff/cache   available
Mem:           7557         193        6822          12         541        6725
Swap:          4095           0        4095

With this patch:
[root@zzxx-yy10 ~]# free -m
              total        used        free      shared  buff/cache   available
Mem:           8133         194        7464          12         475        7338
Swap:          4095           0        4095

Changes made here are completely transparent to how fadump has
traditionally worked.

Thanks to Aneesh Kumar and Anshuman Khandual for helping us understand
CMA and its usage.

TODO:
- Handle case where CMA reservation spans nodes.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---
 Documentation/powerpc/firmware-assisted-dump.txt |   17 ++++
 arch/powerpc/include/asm/fadump.h                |    5 +
 arch/powerpc/kernel/fadump.c                     |   97 ++++++++++++++++++++--
 3 files changed, 108 insertions(+), 11 deletions(-)

diff --git a/Documentation/powerpc/firmware-assisted-dump.txt b/Documentation/powerpc/firmware-assisted-dump.txt
index bdd344aa18d9..18c5feef2577 100644
--- a/Documentation/powerpc/firmware-assisted-dump.txt
+++ b/Documentation/powerpc/firmware-assisted-dump.txt
@@ -113,7 +113,15 @@ header, is usually reserved at an offset greater than boot memory
 size (see Fig. 1). This area is *not* released: this region will
 be kept permanently reserved, so that it can act as a receptacle
 for a copy of the boot memory content in addition to CPU state
-and HPTE region, in the case a crash does occur.
+and HPTE region, in the case a crash does occur. Since this reserved
+memory area is used only after the system crash, there is no point in
+blocking this significant chunk of memory from production kernel.
+Hence, the implementation uses the Linux kernel's Contiguous Memory
+Allocator (CMA) for memory reservation if CMA is configured for kernel.
+With CMA reservation this memory will be available for applications to
+use it, while kernel is prevented from using it. With this fadump will
+still be able to capture all of the kernel memory and most of the user
+space memory except the user pages that were present in CMA region.
 
   o Memory Reservation during first kernel
 
@@ -162,6 +170,9 @@ How to enable firmware-assisted dump (fadump):
 
 1. Set config option CONFIG_FA_DUMP=y and build kernel.
 2. Boot into linux kernel with 'fadump=on' kernel cmdline option.
+   By default, fadump reserved memory will be initialized as CMA area.
+   Alternatively, user can boot linux kernel with 'fadump=nocma' to
+   prevent fadump to use CMA.
 3. Optionally, user can also set 'crashkernel=' kernel cmdline
    to specify size of the memory to reserve for boot memory dump
    preservation.
@@ -172,6 +183,10 @@ NOTE: 1. 'fadump_reserve_mem=' parameter has been deprecated. Instead
       2. If firmware-assisted dump fails to reserve memory then it
          will fallback to existing kdump mechanism if 'crashkernel='
          option is set at kernel cmdline.
+      3. if user wants to capture all of user space memory and ok with
+         reserved memory not available to production system, then
+         'fadump=nocma' kernel parameter can be used to fallback to
+         old behaviour.
 
 Sysfs/debugfs files:
 ------------
diff --git a/arch/powerpc/include/asm/fadump.h b/arch/powerpc/include/asm/fadump.h
index 5a23010af600..e9764b541927 100644
--- a/arch/powerpc/include/asm/fadump.h
+++ b/arch/powerpc/include/asm/fadump.h
@@ -48,6 +48,10 @@
 
 #define memblock_num_regions(memblock_type)	(memblock.memblock_type.cnt)
 
+/* Alignement per CMA requirement. */
+#define FADUMP_CMA_ALIGNMENT	(PAGE_SIZE <<				\
+			max_t(unsigned long, MAX_ORDER - 1, pageblock_order))
+
 /* Firmware provided dump sections */
 #define FADUMP_CPU_STATE_DATA	0x0001
 #define FADUMP_HPTE_REGION	0x0002
@@ -141,6 +145,7 @@ struct fw_dump {
 	unsigned long	fadump_supported:1;
 	unsigned long	dump_active:1;
 	unsigned long	dump_registered:1;
+	unsigned long	nocma:1;
 };
 
 /*
diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
index 07e8396d472b..166e71635921 100644
--- a/arch/powerpc/kernel/fadump.c
+++ b/arch/powerpc/kernel/fadump.c
@@ -34,6 +34,7 @@
 #include <linux/crash_dump.h>
 #include <linux/kobject.h>
 #include <linux/sysfs.h>
+#include <linux/cma.h>
 
 #include <asm/debugfs.h>
 #include <asm/page.h>
@@ -45,11 +46,75 @@
 static struct fw_dump fw_dump;
 static struct fadump_mem_struct fdm;
 static const struct fadump_mem_struct *fdm_active;
+#ifdef CONFIG_CMA
+static struct cma *fadump_cma;
+#endif
 
 static DEFINE_MUTEX(fadump_mutex);
 struct fad_crash_memory_ranges crash_memory_ranges[INIT_CRASHMEM_RANGES];
 int crash_mem_ranges;
 
+#ifdef CONFIG_CMA
+/*
+ * fadump_cma_init() - Initialize CMA area from a fadump reserved memory
+ *
+ * This function initializes CMA area from fadump reserved memory.
+ * The total size of fadump reserved memory covers for boot memory size
+ * + cpu data size + hpte size and metadata.
+ * Initialize only the area equivalent to boot memory size for CMA use.
+ * The reamining portion of fadump reserved memory will be not given
+ * to CMA and pages for thoes will stay reserved. boot memory size is
+ * aligned per CMA requirement to satisy cma_init_reserved_mem() call.
+ * But for some reason even if it fails we still have the memory reservation
+ * with us and we can still continue doing fadump.
+ */
+int __init fadump_cma_init(void)
+{
+	unsigned long long base, size;
+	int rc;
+
+	if (!fw_dump.fadump_enabled)
+		return 0;
+
+	/*
+	 * Do not use CMA if user has provided fadump=nocma kernel parameter.
+	 * Return 1 to continue with fadump old behaviour.
+	 */
+	if (fw_dump.nocma)
+		return 1;
+
+	base = fw_dump.reserve_dump_area_start;
+	size = fw_dump.boot_memory_size;
+
+	if (!size)
+		return 0;
+
+	rc = cma_init_reserved_mem(base, size, 0, "fadump_cma", &fadump_cma);
+	if (rc) {
+		pr_err("Failed to init cma area for firmware-assisted dump,%d\n", rc);
+		/*
+		 * Though the CMA init has failed we still have memory
+		 * reservation with us. The reserved memory will be
+		 * blocked from production system usage.  Hence return 1,
+		 * so that we can continue with fadump.
+		 */
+		return 1;
+	}
+
+	/*
+	 * So we now have successfully initialized cma area for fadump.
+	 */
+	pr_info("Initialized 0x%lx bytes cma area at %ldMB from 0x%lx "
+		"bytes of memory reserved for firmware-assisted dump\n",
+		cma_get_size(fadump_cma),
+		(unsigned long)cma_get_base(fadump_cma) >> 20,
+		fw_dump.reserve_dump_area_size);
+	return 1;
+}
+#else
+static int __init fadump_cma_init(void) { return 1; }
+#endif /* CONFIG_CMA */
+
 /* Scan the Firmware Assisted dump configuration details. */
 int __init early_init_dt_scan_fw_dump(unsigned long node,
 			const char *uname, int depth, void *data)
@@ -375,8 +440,15 @@ int __init fadump_reserve_mem(void)
 	 */
 	if (fdm_active)
 		fw_dump.boot_memory_size = be64_to_cpu(fdm_active->rmr_region.source_len);
-	else
+	else {
 		fw_dump.boot_memory_size = fadump_calculate_reserve_size();
+#ifdef CONFIG_CMA
+		if (!fw_dump.nocma)
+			fw_dump.boot_memory_size =
+				ALIGN(fw_dump.boot_memory_size,
+							FADUMP_CMA_ALIGNMENT);
+#endif
+	}
 
 	/*
 	 * Calculate the memory boundary.
@@ -423,8 +495,9 @@ int __init fadump_reserve_mem(void)
 		fw_dump.fadumphdr_addr =
 				be64_to_cpu(fdm_active->rmr_region.destination_address) +
 				be64_to_cpu(fdm_active->rmr_region.source_len);
-		pr_debug("fadumphdr_addr = %p\n",
-				(void *) fw_dump.fadumphdr_addr);
+		pr_debug("fadumphdr_addr = %pa\n", &fw_dump.fadumphdr_addr);
+		fw_dump.reserve_dump_area_start = base;
+		fw_dump.reserve_dump_area_size = size;
 	} else {
 		size = get_fadump_area_size();
 
@@ -452,10 +525,11 @@ int __init fadump_reserve_mem(void)
 			(unsigned long)(size >> 20),
 			(unsigned long)(base >> 20),
 			(unsigned long)(memblock_phys_mem_size() >> 20));
-	}
 
-	fw_dump.reserve_dump_area_start = base;
-	fw_dump.reserve_dump_area_size = size;
+		fw_dump.reserve_dump_area_start = base;
+		fw_dump.reserve_dump_area_size = size;
+		return fadump_cma_init();
+	}
 	return 1;
 }
 
@@ -474,6 +548,10 @@ static int __init early_fadump_param(char *p)
 		fw_dump.fadump_enabled = 1;
 	else if (strncmp(p, "off", 3) == 0)
 		fw_dump.fadump_enabled = 0;
+	else if (strncmp(p, "nocma", 5) == 0) {
+		fw_dump.fadump_enabled = 1;
+		fw_dump.nocma = 1;
+	}
 
 	return 0;
 }
@@ -1146,7 +1224,7 @@ static int fadump_unregister_dump(struct fadump_mem_struct *fdm)
 	return 0;
 }
 
-static int fadump_invalidate_dump(struct fadump_mem_struct *fdm)
+static int fadump_invalidate_dump(const struct fadump_mem_struct *fdm)
 {
 	int rc = 0;
 	unsigned int wait_time;
@@ -1177,9 +1255,8 @@ void fadump_cleanup(void)
 {
 	/* Invalidate the registration only if dump is active. */
 	if (fw_dump.dump_active) {
-		init_fadump_mem_struct(&fdm,
-			be64_to_cpu(fdm_active->cpu_state_data.destination_address));
-		fadump_invalidate_dump(&fdm);
+		/* pass the same memory dump structure provided by platform */
+		fadump_invalidate_dump(fdm_active);
 	} else if (fw_dump.dump_registered) {
 		/* Un-register Firmware-assisted dump if it was registered. */
 		fadump_unregister_dump(&fdm);

Re: [v7,1/3] powerpc/fadump: Reservationless firmware assisted dump

[Michael Ellerman]

On Mon, 2018-08-20 at 08:17:17 UTC, Mahesh J Salgaonkar wrote:
> From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> 
> One of the primary issues with Firmware Assisted Dump (fadump) on Power
> is that it needs a large amount of memory to be reserved. On large
> systems with TeraBytes of memory, this reservation can be quite
> significant.
> 
> In some cases, fadump fails if the memory reserved is insufficient, or
> if the reserved memory was DLPAR hot-removed.
> 
> In the normal case, post reboot, the preserved memory is filtered to
> extract only relevant areas of interest using the makedumpfile tool.
> While the tool provides flexibility to determine what needs to be part
> of the dump and what memory to filter out, all supported distributions
> default this to "Capture only kernel data and nothing else".
> 
> We take advantage of this default and the Linux kernel's Contiguous
> Memory Allocator (CMA) to fundamentally change the memory reservation
> model for fadump.
> 
> Instead of setting aside a significant chunk of memory nobody can use,
> this patch uses CMA instead, to reserve a significant chunk of memory
> that the kernel is prevented from using (due to MIGRATE_CMA), but
> applications are free to use it. With this fadump will still be able
> to capture all of the kernel memory and most of the user space memory
> except the user pages that were present in CMA region.
> 
> Essentially, on a P9 LPAR with 2 cores, 8GB RAM and current upstream:
> [root@zzxx-yy10 ~]# free -m
>               total        used        free      shared  buff/cache   available
> Mem:           7557         193        6822          12         541        6725
> Swap:          4095           0        4095
> 
> With this patch:
> [root@zzxx-yy10 ~]# free -m
>               total        used        free      shared  buff/cache   available
> Mem:           8133         194        7464          12         475        7338
> Swap:          4095           0        4095
> 
> Changes made here are completely transparent to how fadump has
> traditionally worked.
> 
> Thanks to Aneesh Kumar and Anshuman Khandual for helping us understand
> CMA and its usage.
> 
> TODO:
> - Handle case where CMA reservation spans nodes.
> 
> Signed-off-by: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
> Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/a4e92ce8e4c8275bacfe3529d6ac85

cheers

[PATCH v7 2/3] powerpc/fadump: throw proper error message on fadump registration failure.

[Mahesh J Salgaonkar]

From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>

fadump fails to register when there are holes in reserved memory area.
This can happen if user has hot-removed a memory that falls in the fadump
reserved memory area. Throw a meaningful error message to the user in
such case.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/fadump.c |   33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
index 166e71635921..44a29e4d419c 100644
--- a/arch/powerpc/kernel/fadump.c
+++ b/arch/powerpc/kernel/fadump.c
@@ -234,6 +234,36 @@ static int is_boot_memory_area_contiguous(void)
 	return ret;
 }
 
+/*
+ * Returns 1, if there are no holes in reserved memory area,
+ * 0 otherwise.
+ */
+static int is_reserved_memory_area_contiguous(void)
+{
+	struct memblock_region *reg;
+	unsigned long start, end;
+	unsigned long d_start = fw_dump.reserve_dump_area_start;
+	unsigned long d_end = d_start + fw_dump.reserve_dump_area_size;
+	int ret = 0;
+
+	for_each_memblock(memory, reg) {
+		start = max(d_start, (unsigned long)reg->base);
+		end = min(d_end, (unsigned long)(reg->base + reg->size));
+		if (d_start < end) {
+			/* Memory hole from d_start to start */
+			if (start > d_start)
+				break;
+
+			if (end == d_end) {
+				ret = 1;
+				break;
+			}
+			d_start = end + 1;
+		}
+	}
+	return ret;
+}
+
 /* Print firmware assisted dump configurations for debugging purpose. */
 static void fadump_show_config(void)
 {
@@ -602,6 +632,9 @@ static int register_fw_dump(struct fadump_mem_struct *fdm)
 		if (!is_boot_memory_area_contiguous())
 			pr_err("Can't have holes in boot memory area while "
 			       "registering fadump\n");
+		else if (!is_reserved_memory_area_contiguous())
+			pr_err("Can't have holes in reserved memory area while"
+			       " registering fadump\n");
 
 		printk(KERN_ERR "Failed to register firmware-assisted kernel"
 			" dump. Parameter Error(%d).\n", rc);

[PATCH v7 3/3] powerpc/fadump: Do not allow hot-remove memory from fadump reserved area.

[Mahesh J Salgaonkar]

From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>

For fadump to work successfully there should not be any holes in reserved
memory ranges where kernel has asked firmware to move the content of old
kernel memory in event of crash. Now that fadump uses CMA for reserved
area, this memory area is now not protected from hot-remove operations
unless it is cma allocated. Hence, fadump service can fail to re-register
after the hot-remove operation, if hot-removed memory belongs to fadump
reserved region. To avoid this make sure that memory from fadump reserved
area is not hot-removable if fadump is registered.

However, if user still wants to remove that memory, he can do so by
manually stopping fadump service before hot-remove operation.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/fadump.h               |    2 +-
 arch/powerpc/kernel/fadump.c                    |   10 ++++++++--
 arch/powerpc/platforms/pseries/hotplug-memory.c |    7 +++++--
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/fadump.h b/arch/powerpc/include/asm/fadump.h
index e9764b541927..43825111c479 100644
--- a/arch/powerpc/include/asm/fadump.h
+++ b/arch/powerpc/include/asm/fadump.h
@@ -208,7 +208,7 @@ struct fad_crash_memory_ranges {
 	unsigned long long	size;
 };
 
-extern int is_fadump_boot_memory_area(u64 addr, ulong size);
+extern int is_fadump_memory_area(u64 addr, ulong size);
 extern int early_init_dt_scan_fw_dump(unsigned long node,
 		const char *uname, int depth, void *data);
 extern int fadump_reserve_mem(void);
diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
index 44a29e4d419c..89bee4f4fe5c 100644
--- a/arch/powerpc/kernel/fadump.c
+++ b/arch/powerpc/kernel/fadump.c
@@ -180,13 +180,19 @@ int __init early_init_dt_scan_fw_dump(unsigned long node,
 
 /*
  * If fadump is registered, check if the memory provided
- * falls within boot memory area.
+ * falls within boot memory area and reserved memory area.
  */
-int is_fadump_boot_memory_area(u64 addr, ulong size)
+int is_fadump_memory_area(u64 addr, ulong size)
 {
+	u64 d_start = fw_dump.reserve_dump_area_start;
+	u64 d_end = d_start + fw_dump.reserve_dump_area_size;
+
 	if (!fw_dump.dump_registered)
 		return 0;
 
+	if (((addr + size) > d_start) && (addr <= d_end))
+		return 1;
+
 	return (addr + size) > RMA_START && addr <= fw_dump.boot_memory_size;
 }
 
diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index c1578f54c626..e4c658cda3a7 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -389,8 +389,11 @@ static bool lmb_is_removable(struct drmem_lmb *lmb)
 	phys_addr = lmb->base_addr;
 
 #ifdef CONFIG_FA_DUMP
-	/* Don't hot-remove memory that falls in fadump boot memory area */
-	if (is_fadump_boot_memory_area(phys_addr, block_sz))
+	/*
+	 * Don't hot-remove memory that falls in fadump boot memory area
+	 * and memory that is reserved for capturing old kernel memory.
+	 */
+	if (is_fadump_memory_area(phys_addr, block_sz))
 		return false;
 #endif