Subject: [PATCH v5 09/10] powerpc/pmem: Disable synchronous fault by default

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 10 Jun 2020 11:53:42 +0530

This adds a kernel config option that controls whether MAP_SYNC is enabled by
default. With POWER10, architecture is adding new pmem flush and sync
instructions. The kernel should prevent the usage of MAP_SYNC if applications
are not using the new instructions on newer hardware.

This config allows user to control whether MAP_SYNC should be enabled by
default or not.

Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 arch/powerpc/platforms/Kconfig.cputype    |  9 +++++++++
 arch/powerpc/platforms/pseries/papr_scm.c | 17 ++++++++++++++++-
 drivers/nvdimm/of_pmem.c                  |  7 +++++++
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index d349603fb889..abcc163b8dc6 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -383,6 +383,15 @@ config PPC_KUEP
 
 	  If you're unsure, say Y.
 
+config ARCH_MAP_SYNC_DISABLE
+	bool "Disable synchronous fault support (MAP_SYNC)"
+	default y
+	help
+	  Disable support for synchronous fault with nvdimm namespaces.
+
+	  If you're unsure, say Y.
+
+
 config PPC_HAVE_KUAP
 	bool
 
diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
index ad506e7003c9..b970d2dbe589 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/arch/powerpc/platforms/pseries/papr_scm.c
@@ -30,6 +30,7 @@ struct papr_scm_priv {
 	uint64_t block_size;
 	int metadata_size;
 	bool is_volatile;
+	bool disable_map_sync;
 
 	uint64_t bound_addr;
 
@@ -353,11 +354,18 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
 	ndr_desc.num_mappings = 1;
 	ndr_desc.nd_set = &p->nd_set;
 	ndr_desc.flush = papr_scm_flush_sync;
+	set_bit(ND_REGION_SYNC_ENABLED, &ndr_desc.flags);
 
 	if (p->is_volatile)
 		p->region = nvdimm_volatile_region_create(p->bus, &ndr_desc);
 	else {
 		set_bit(ND_REGION_PERSIST_MEMCTRL, &ndr_desc.flags);
+		/*
+		 * for a persistent region, check if the platform needs to
+		 * force MAP_SYNC disable.
+		 */
+		if (p->disable_map_sync)
+			clear_bit(ND_REGION_SYNC_ENABLED, &ndr_desc.flags);
 		p->region = nvdimm_pmem_region_create(p->bus, &ndr_desc);
 	}
 	if (!p->region) {
@@ -378,7 +386,7 @@ err:	nvdimm_bus_unregister(p->bus);
 
 static int papr_scm_probe(struct platform_device *pdev)
 {
-	struct device_node *dn = pdev->dev.of_node;
+	struct device_node *dn;
 	u32 drc_index, metadata_size;
 	u64 blocks, block_size;
 	struct papr_scm_priv *p;
@@ -386,6 +394,10 @@ static int papr_scm_probe(struct platform_device *pdev)
 	u64 uuid[2];
 	int rc;
 
+	dn = dev_of_node(&pdev->dev);
+	if (!dn)
+		return -ENXIO;
+
 	/* check we have all the required DT properties */
 	if (of_property_read_u32(dn, "ibm,my-drc-index", &drc_index)) {
 		dev_err(&pdev->dev, "%pOF: missing drc-index!\n", dn);
@@ -415,6 +427,9 @@ static int papr_scm_probe(struct platform_device *pdev)
 	/* optional DT properties */
 	of_property_read_u32(dn, "ibm,metadata-size", &metadata_size);
 
+	if (of_device_is_compatible(dn, "ibm,pmemory-v2"))
+		p->disable_map_sync = true;
+
 	p->dn = dn;
 	p->drc_index = drc_index;
 	p->block_size = block_size;
diff --git a/drivers/nvdimm/of_pmem.c b/drivers/nvdimm/of_pmem.c
index 6826a274a1f1..a6cc3488e552 100644
--- a/drivers/nvdimm/of_pmem.c
+++ b/drivers/nvdimm/of_pmem.c
@@ -59,12 +59,19 @@ static int of_pmem_region_probe(struct platform_device *pdev)
 		ndr_desc.res = &pdev->resource[i];
 		ndr_desc.of_node = np;
 		set_bit(ND_REGION_PAGEMAP, &ndr_desc.flags);
+		set_bit(ND_REGION_SYNC_ENABLED, &ndr_desc.flags);
 
 		if (is_volatile)
 			region = nvdimm_volatile_region_create(bus, &ndr_desc);
 		else {
 			set_bit(ND_REGION_PERSIST_MEMCTRL, &ndr_desc.flags);
+			/*
+			 * for a persistent region, check for newer device
+			 */
+			if (of_device_is_compatible(np, "pmem-region-v2"))
+				clear_bit(ND_REGION_SYNC_ENABLED, &ndr_desc.flags);
 			region = nvdimm_pmem_region_create(bus, &ndr_desc);
+
 		}
 
 		if (!region)
-- 
2.26.2