Re: [PATCH v3 3/6] mm/nvdimm: Add page size and struct page size to pfn superblock

[Jan Kara]

On Tue 04-06-19 14:43:54, Aneesh Kumar K.V wrote:
> This is needed so that we don't wrongly initialize a namespace
> which doesn't have enough space reserved for holding struct pages
> with the current kernel.
> 
> We also increment PFN_MIN_VERSION to make sure that older kernel
> won't initialize namespace created with newer kernel.
> 
> Signed-off-by: Aneesh Kumar K.V 
...
> diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c
> index 00c57805cad3..e01eee9efafe 100644
> --- a/drivers/nvdimm/pfn_devs.c
> +++ b/drivers/nvdimm/pfn_devs.c
> @@ -467,6 +467,15 @@ int nd_pfn_validate(struct nd_pfn *nd_pfn, const char 
> *sig)
>   if (__le16_to_cpu(pfn_sb->version_minor) < 2)
>   pfn_sb->align = 0;
>  
> + if (__le16_to_cpu(pfn_sb->version_minor) < 3) {
> + /*
> +  * For a large part we use PAGE_SIZE. But we
> +  * do have some accounting code using SZ_4K.
> +  */
> + pfn_sb->page_struct_size = cpu_to_le16(64);
> + pfn_sb->page_size = cpu_to_le32(SZ_4K);
> + }
> +
>   switch (le32_to_cpu(pfn_sb->mode)) {
>   case PFN_MODE_RAM:
>   case PFN_MODE_PMEM:

As we discussed with Aneesh privately, this actually means that existing
NVDIMM namespaces on PPC64 will stop working due to these defaults for old
superblocks. I don't think that's a good thing as upgrading kernels is
going to be nightmare due to this on PPC64. So I believe we should make
defaults for old superblocks such that working setups keep working without
sysadmin having to touch anything.

Honza
-- 
Jan Kara 
SUSE Labs, CR

[PATCH v3 3/6] mm/nvdimm: Add page size and struct page size to pfn superblock

[Aneesh Kumar K.V]

This is needed so that we don't wrongly initialize a namespace
which doesn't have enough space reserved for holding struct pages
with the current kernel.

We also increment PFN_MIN_VERSION to make sure that older kernel
won't initialize namespace created with newer kernel.

Signed-off-by: Aneesh Kumar K.V 
---
 drivers/nvdimm/pfn.h  |  7 +--
 drivers/nvdimm/pfn_devs.c | 27 ++-
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/drivers/nvdimm/pfn.h b/drivers/nvdimm/pfn.h
index 5fd29242745a..ba11738ca8a2 100644
--- a/drivers/nvdimm/pfn.h
+++ b/drivers/nvdimm/pfn.h
@@ -25,7 +25,7 @@
  * kernel should fail to initialize that namespace.
  */
 
-#define PFN_MIN_VERSION 0
+#define PFN_MIN_VERSION 1
 
 struct nd_pfn_sb {
u8 signature[PFN_SIG_LEN];
@@ -43,7 +43,10 @@ struct nd_pfn_sb {
/* minor-version-2 record the base alignment of the mapping */
__le32 align;
__le16 min_version;
-   u8 padding[3998];
+   /* minor-version-3 record the page size and struct page size */
+   __le16 page_struct_size;
+   __le32 page_size;
+   u8 padding[3992];
__le64 checksum;
 };
 
diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c
index 00c57805cad3..e01eee9efafe 100644
--- a/drivers/nvdimm/pfn_devs.c
+++ b/drivers/nvdimm/pfn_devs.c
@@ -467,6 +467,15 @@ int nd_pfn_validate(struct nd_pfn *nd_pfn, const char *sig)
if (__le16_to_cpu(pfn_sb->version_minor) < 2)
pfn_sb->align = 0;
 
+   if (__le16_to_cpu(pfn_sb->version_minor) < 3) {
+   /*
+* For a large part we use PAGE_SIZE. But we
+* do have some accounting code using SZ_4K.
+*/
+   pfn_sb->page_struct_size = cpu_to_le16(64);
+   pfn_sb->page_size = cpu_to_le32(SZ_4K);
+   }
+
switch (le32_to_cpu(pfn_sb->mode)) {
case PFN_MODE_RAM:
case PFN_MODE_PMEM:
@@ -482,6 +491,20 @@ int nd_pfn_validate(struct nd_pfn *nd_pfn, const char *sig)
align = 1UL << ilog2(offset);
mode = le32_to_cpu(pfn_sb->mode);
 
+   if (le32_to_cpu(pfn_sb->page_size) != PAGE_SIZE) {
+   dev_err(_pfn->dev,
+   "init failed, page size mismatch %d\n",
+   le32_to_cpu(pfn_sb->page_size));
+   return -EOPNOTSUPP;
+   }
+
+   if (le16_to_cpu(pfn_sb->page_struct_size) != sizeof(struct page)) {
+   dev_err(_pfn->dev,
+   "init failed, struct page size mismatch %d\n",
+   le16_to_cpu(pfn_sb->page_struct_size));
+   return -EOPNOTSUPP;
+   }
+
if (!nd_pfn->uuid) {
/*
 * When probing a namepace via nd_pfn_probe() the uuid
@@ -776,11 +799,13 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
memcpy(pfn_sb->uuid, nd_pfn->uuid, 16);
memcpy(pfn_sb->parent_uuid, nd_dev_to_uuid(>dev), 16);
pfn_sb->version_major = cpu_to_le16(1);
-   pfn_sb->version_minor = cpu_to_le16(2);
+   pfn_sb->version_minor = cpu_to_le16(3);
pfn_sb->min_version = cpu_to_le16(PFN_MIN_VERSION);
pfn_sb->start_pad = cpu_to_le32(start_pad);
pfn_sb->end_trunc = cpu_to_le32(end_trunc);
pfn_sb->align = cpu_to_le32(nd_pfn->align);
+   pfn_sb->page_struct_size = cpu_to_le16(sizeof(struct page));
+   pfn_sb->page_size = cpu_to_le32(PAGE_SIZE);
checksum = nd_sb_checksum((struct nd_gen_sb *) pfn_sb);
pfn_sb->checksum = cpu_to_le64(checksum);
 
-- 
2.21.0