Signed-off-by: Zhang Yi <yi.z.zhang@linux.intel.com>
---
 docs/nvdimm.txt | 21 ++++++++++++++++++++-
 qemu-options.hx |  4 ++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
index 5f158a6..565ba73 100644
--- a/docs/nvdimm.txt
+++ b/docs/nvdimm.txt
@@ -142,11 +142,30 @@ backend of vNVDIMM:
 Guest Data Persistence
 ----------------------
 
+vNVDIMM is designed and implemented to guarantee the guest data
+persistence on the backends even on the host crash and power
+failures. However, there are still some requirements and limitations
+as explained below.
+
 Though QEMU supports multiple types of vNVDIMM backends on Linux,
-currently the only one that can guarantee the guest write persistence
+if MAP_SYNC is not supported by the host kernel and the backends,
+the only backend that can guarantee the guest write persistence
 is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to
 which all guest access do not involve any host-side kernel cache.
 
+mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such
+systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure
+filesystem metadata consistent even after a system crash or power
+failure. Besides the host kernel support, enabling MAP_SYNC in QEMU
+also requires:
+
+ - the backend is a file supporting DAX, e.g., a file on an ext4 or
+   xfs file system mounted with '-o dax',
+
+ - 'share' option of memory-backend-file is 'on'.
+
+ - 'pmem' option of memory-backend-file is 'on'
+
 When using other types of backends, it's suggested to set 'unarmed'
 option of '-device nvdimm' to 'on', which sets the unarmed flag of the
 guest NVDIMM region mapping structure.  This unarmed flag indicates
diff --git a/qemu-options.hx b/qemu-options.hx
index 08f8516..545cb8a 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel NVDIMM).
 If @option{pmem} is set to 'on', QEMU will take necessary operations to
 guarantee the persistence of its own writes to @option{mem-path}
 (e.g. in vNVDIMM label emulation and live migration).
+Also, we will map the backend-file with MAP_SYNC flag, which can ensure
+the file metadata is in sync to @option{mem-path} even on the host crash
+and power failures. MAP_SYNC requires supports from both the host kernel
+(since Linux kernel 4.15) and @option{mem-path} (only files supporting DAX).
 
 @item -object memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave}
 
-- 
2.7.4

On Wed, Jan 16, 2019 at 04:11:16PM +0800, Zhang Yi wrote:
> Signed-off-by: Zhang Yi <yi.z.zhang@linux.intel.com>
> ---
>  docs/nvdimm.txt | 21 ++++++++++++++++++++-
>  qemu-options.hx |  4 ++++
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
> index 5f158a6..565ba73 100644
> --- a/docs/nvdimm.txt
> +++ b/docs/nvdimm.txt
> @@ -142,11 +142,30 @@ backend of vNVDIMM:
>  Guest Data Persistence
>  ----------------------
>  
> +vNVDIMM is designed and implemented to guarantee the guest data
> +persistence on the backends even on the host crash and power

in case of a host crash or a power failure

(be consistent)

> +failures. However, there are still some requirements and limitations
> +as explained below.
> +
>  Though QEMU supports multiple types of vNVDIMM backends on Linux,
> -currently the only one that can guarantee the guest write persistence
> +if MAP_SYNC is not supported by the host kernel and the backends,
> +the only backend that can guarantee the guest write persistence
>  is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to
>  which all guest access do not involve any host-side kernel cache.
>  
> +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such
> +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure

which ensures

> +filesystem metadata consistent

consistency

> even after a system crash or power

a power

> +failure. Besides the host kernel support, enabling MAP_SYNC in QEMU
> +also requires:
> +
> + - the backend is a file supporting DAX, e.g., a file on an ext4 or
> +   xfs file system mounted with '-o dax',
> +
> + - 'share' option of memory-backend-file is 'on'.

why does share need to be on?

> +
> + - 'pmem' option of memory-backend-file is 'on'
> +
>  When using other types of backends, it's suggested to set 'unarmed'
>  option of '-device nvdimm' to 'on', which sets the unarmed flag of the
>  guest NVDIMM region mapping structure.  This unarmed flag indicates
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 08f8516..545cb8a 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel NVDIMM).
>  If @option{pmem} is set to 'on', QEMU will take necessary operations to
>  guarantee the persistence of its own writes to @option{mem-path}
>  (e.g. in vNVDIMM label emulation and live migration).
> +Also, we will map the backend-file with MAP_SYNC flag, which can ensure
> +the file metadata is in sync to @option{mem-path} even on the host crash
> +and power failures. MAP_SYNC requires supports from both the host kernel

requires support

> +(since Linux kernel 4.15) and @option{mem-path} (only files supporting DAX).
>  
>  @item -object memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave}
>  
> -- 
> 2.7.4

On 2019-01-16 at 10:40:23 -0500, Michael S. Tsirkin wrote:
> On Wed, Jan 16, 2019 at 04:11:16PM +0800, Zhang Yi wrote:
> > Signed-off-by: Zhang Yi <yi.z.zhang@linux.intel.com>
> > ---
> >  docs/nvdimm.txt | 21 ++++++++++++++++++++-
> >  qemu-options.hx |  4 ++++
> >  2 files changed, 24 insertions(+), 1 deletion(-)
> > 
> > diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
> > index 5f158a6..565ba73 100644
> > --- a/docs/nvdimm.txt
> > +++ b/docs/nvdimm.txt
> > @@ -142,11 +142,30 @@ backend of vNVDIMM:
> >  Guest Data Persistence
> >  ----------------------
> >  
> > +vNVDIMM is designed and implemented to guarantee the guest data
> > +persistence on the backends even on the host crash and power
> 
> in case of a host crash or a power failure
> 
> (be consistent)
> 
> > +failures. However, there are still some requirements and limitations
> > +as explained below.
> > +
> >  Though QEMU supports multiple types of vNVDIMM backends on Linux,
> > -currently the only one that can guarantee the guest write persistence
> > +if MAP_SYNC is not supported by the host kernel and the backends,
> > +the only backend that can guarantee the guest write persistence
> >  is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to
> >  which all guest access do not involve any host-side kernel cache.
> >  
> > +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such
> > +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure
> 
> which ensures
> 
> > +filesystem metadata consistent
> 
> consistency
> 
> > even after a system crash or power
> 
> a power
> 
> > +failure. Besides the host kernel support, enabling MAP_SYNC in QEMU
> > +also requires:
> > +
> > + - the backend is a file supporting DAX, e.g., a file on an ext4 or
> > +   xfs file system mounted with '-o dax',
> > +
> > + - 'share' option of memory-backend-file is 'on'.
> 
> why does share need to be on?
According to mmap(2) man page, 
MAP_SYNC is available only with the MAP_SHARED_VALIDATE map‐ping type.
I will add this to documentation, Thanks.
> 
> > +
> > + - 'pmem' option of memory-backend-file is 'on'
> > +
> >  When using other types of backends, it's suggested to set 'unarmed'
> >  option of '-device nvdimm' to 'on', which sets the unarmed flag of the
> >  guest NVDIMM region mapping structure.  This unarmed flag indicates
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 08f8516..545cb8a 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel NVDIMM).
> >  If @option{pmem} is set to 'on', QEMU will take necessary operations to
> >  guarantee the persistence of its own writes to @option{mem-path}
> >  (e.g. in vNVDIMM label emulation and live migration).
> > +Also, we will map the backend-file with MAP_SYNC flag, which can ensure
> > +the file metadata is in sync to @option{mem-path} even on the host crash
> > +and power failures. MAP_SYNC requires supports from both the host kernel
> 
> requires support
> 
> > +(since Linux kernel 4.15) and @option{mem-path} (only files supporting DAX).
> >  
> >  @item -object memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave}
> >  
> > -- 
> > 2.7.4

> > > ---
> > >  docs/nvdimm.txt | 21 ++++++++++++++++++++-
> > >  qemu-options.hx |  4 ++++
> > >  2 files changed, 24 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
> > > index 5f158a6..565ba73 100644
> > > --- a/docs/nvdimm.txt
> > > +++ b/docs/nvdimm.txt
> > > @@ -142,11 +142,30 @@ backend of vNVDIMM:
> > >  Guest Data Persistence
> > >  ----------------------
> > >  
> > > +vNVDIMM is designed and implemented to guarantee the guest data
> > > +persistence on the backends even on the host crash and power
> > 
> > in case of a host crash or a power failure
> > 
> > (be consistent)
> > 
> > > +failures. However, there are still some requirements and limitations
> > > +as explained below.
> > > +
> > >  Though QEMU supports multiple types of vNVDIMM backends on Linux,
> > > -currently the only one that can guarantee the guest write persistence
> > > +if MAP_SYNC is not supported by the host kernel and the backends,
> > > +the only backend that can guarantee the guest write persistence
> > >  is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to
> > >  which all guest access do not involve any host-side kernel cache.
> > >  
> > > +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such
> > > +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure
> > 
> > which ensures
> > 
> > > +filesystem metadata consistent
> > 
> > consistency
> > 
> > > even after a system crash or power
> > 
> > a power
> > 
> > > +failure. Besides the host kernel support, enabling MAP_SYNC in QEMU
> > > +also requires:
> > > +
> > > + - the backend is a file supporting DAX, e.g., a file on an ext4 or
> > > +   xfs file system mounted with '-o dax',
> > > +
> > > + - 'share' option of memory-backend-file is 'on'.
> > 
> > why does share need to be on?
> According to mmap(2) man page,
> MAP_SYNC is available only with the MAP_SHARED_VALIDATE map‐ping type.
> I will add this to documentation, Thanks.

MAP_SHARE_VALIDATE should be used to validate MAP_SYNC with MAP_SHARED.

#define MAP_SHARED_VALIDATE 0x03

In contrast, MAP_SHARED is:
#define MAP_SHARED      0x01            /* Share changes */

I think we should use MAP_SHARED_VALIDATE with MAP_SYNC here?

Thanks,
Pankaj 

> > 
> > > +
> > > + - 'pmem' option of memory-backend-file is 'on'
> > > +
> > >  When using other types of backends, it's suggested to set 'unarmed'
> > >  option of '-device nvdimm' to 'on', which sets the unarmed flag of the
> > >  guest NVDIMM region mapping structure.  This unarmed flag indicates
> > > diff --git a/qemu-options.hx b/qemu-options.hx
> > > index 08f8516..545cb8a 100644
> > > --- a/qemu-options.hx
> > > +++ b/qemu-options.hx
> > > @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel
> > > NVDIMM).
> > >  If @option{pmem} is set to 'on', QEMU will take necessary operations to
> > >  guarantee the persistence of its own writes to @option{mem-path}
> > >  (e.g. in vNVDIMM label emulation and live migration).
> > > +Also, we will map the backend-file with MAP_SYNC flag, which can ensure
> > > +the file metadata is in sync to @option{mem-path} even on the host crash
> > > +and power failures. MAP_SYNC requires supports from both the host kernel
> > 
> > requires support
> > 
> > > +(since Linux kernel 4.15) and @option{mem-path} (only files supporting
> > > DAX).
> > >  
> > >  @item -object
> > >  memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave}
> > >  
> > > --
> > > 2.7.4
> 

On 2019-01-21 at 02:21:39 -0500, Pankaj Gupta wrote:
> 
> > > > ---
> > > >  docs/nvdimm.txt | 21 ++++++++++++++++++++-
> > > >  qemu-options.hx |  4 ++++
> > > >  2 files changed, 24 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
> > > > index 5f158a6..565ba73 100644
> > > > --- a/docs/nvdimm.txt
> > > > +++ b/docs/nvdimm.txt
> > > > @@ -142,11 +142,30 @@ backend of vNVDIMM:
> > > >  Guest Data Persistence
> > > >  ----------------------
> > > >  
> > > > +vNVDIMM is designed and implemented to guarantee the guest data
> > > > +persistence on the backends even on the host crash and power
> > > 
> > > in case of a host crash or a power failure
> > > 
> > > (be consistent)
> > > 
> > > > +failures. However, there are still some requirements and limitations
> > > > +as explained below.
> > > > +
> > > >  Though QEMU supports multiple types of vNVDIMM backends on Linux,
> > > > -currently the only one that can guarantee the guest write persistence
> > > > +if MAP_SYNC is not supported by the host kernel and the backends,
> > > > +the only backend that can guarantee the guest write persistence
> > > >  is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to
> > > >  which all guest access do not involve any host-side kernel cache.
> > > >  
> > > > +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such
> > > > +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure
> > > 
> > > which ensures
> > > 
> > > > +filesystem metadata consistent
> > > 
> > > consistency
> > > 
> > > > even after a system crash or power
> > > 
> > > a power
> > > 
> > > > +failure. Besides the host kernel support, enabling MAP_SYNC in QEMU
> > > > +also requires:
> > > > +
> > > > + - the backend is a file supporting DAX, e.g., a file on an ext4 or
> > > > +   xfs file system mounted with '-o dax',
> > > > +
> > > > + - 'share' option of memory-backend-file is 'on'.
> > > 
> > > why does share need to be on?
> > According to mmap(2) man page,
> > MAP_SYNC is available only with the MAP_SHARED_VALIDATE map‐ping type.
> > I will add this to documentation, Thanks.
> 
> MAP_SHARE_VALIDATE should be used to validate MAP_SYNC with MAP_SHARED.
> 
> #define MAP_SHARED_VALIDATE 0x03
> 
> In contrast, MAP_SHARED is:
> #define MAP_SHARED      0x01            /* Share changes */
> 
> I think we should use MAP_SHARED_VALIDATE with MAP_SYNC here?
> 
> Thanks,
> Pankaj
Yes, Pankaj, Thanks point that out, I will add the MAP_SHARED_VALIDATE.
> 
> > > 
> > > > +
> > > > + - 'pmem' option of memory-backend-file is 'on'
> > > > +
> > > >  When using other types of backends, it's suggested to set 'unarmed'
> > > >  option of '-device nvdimm' to 'on', which sets the unarmed flag of the
> > > >  guest NVDIMM region mapping structure.  This unarmed flag indicates
> > > > diff --git a/qemu-options.hx b/qemu-options.hx
> > > > index 08f8516..545cb8a 100644
> > > > --- a/qemu-options.hx
> > > > +++ b/qemu-options.hx
> > > > @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel
> > > > NVDIMM).
> > > >  If @option{pmem} is set to 'on', QEMU will take necessary operations to
> > > >  guarantee the persistence of its own writes to @option{mem-path}
> > > >  (e.g. in vNVDIMM label emulation and live migration).
> > > > +Also, we will map the backend-file with MAP_SYNC flag, which can ensure
> > > > +the file metadata is in sync to @option{mem-path} even on the host crash
> > > > +and power failures. MAP_SYNC requires supports from both the host kernel
> > > 
> > > requires support
> > > 
> > > > +(since Linux kernel 4.15) and @option{mem-path} (only files supporting
> > > > DAX).
> > > >  
> > > >  @item -object
> > > >  memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave}
> > > >  
> > > > --
> > > > 2.7.4
> >