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Re: [Qemu-devel] [PATCH 3/7 V7 RESEND] hostmem-file: add the 'pmem' opti


From: He, Junyan
Subject: Re: [Qemu-devel] [PATCH 3/7 V7 RESEND] hostmem-file: add the 'pmem' option
Date: Mon, 9 Jul 2018 04:43:08 +0000

Hi:

Do I still need to do something before it can be merged?

Thanks
Junyan


-----Original Message-----
From: Igor Mammedov [mailto:address@hidden 
Sent: Thursday, June 21, 2018 9:20 PM
To: address@hidden
Cc: address@hidden; Haozhong Zhang <address@hidden>; address@hidden; 
address@hidden; address@hidden; address@hidden; address@hidden; address@hidden; 
He, Junyan <address@hidden>; address@hidden; address@hidden; address@hidden
Subject: Re: [Qemu-devel] [PATCH 3/7 V7 RESEND] hostmem-file: add the 'pmem' 
option

On Tue, 19 Jun 2018 11:28:19 +0800
address@hidden wrote:

> From: Junyan He <address@hidden>
> 
> When QEMU emulates vNVDIMM labels and migrates vNVDIMM devices, it 
> needs to know whether the backend storage is a real persistent memory, 
> in order to decide whether special operations should be performed to 
> ensure the data persistence.
> 
> This boolean option 'pmem' allows users to specify whether the backend 
> storage of memory-backend-file is a real persistent memory. If 
> 'pmem=on', QEMU will set the flag RAM_PMEM in the RAM block of the 
> corresponding memory region.
> 
> Signed-off-by: Junyan He <address@hidden>
> Signed-off-by: Haozhong Zhang <address@hidden>
> Reviewed-by: Stefan Hajnoczi <address@hidden>
a couple suggestion wrt patch submission.

1.
do not sent next version of a patch from series on its own, you should rather 
send it as reply to the patch it replaces or resend whole series. to send as 
reply one can use  git send-email --in-reply-to="Message-Id value we are 
replying to" ...

2. it would be nice if you add changelog here after signatures like:

---
vX:
  * the thing that changed wrt X-1

> ---
>  backends/hostmem-file.c | 39 ++++++++++++++++++++++++++++++++++++++-
>  docs/nvdimm.txt         | 18 ++++++++++++++++++
>  exec.c                  |  9 +++++++++
>  include/exec/memory.h   |  4 ++++
>  include/exec/ram_addr.h |  3 +++
>  qemu-options.hx         |  7 +++++++
>  6 files changed, 79 insertions(+), 1 deletion(-)
> 
> diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c index 
> 34c68bb..4607651 100644
> --- a/backends/hostmem-file.c
> +++ b/backends/hostmem-file.c
> @@ -12,6 +12,7 @@
>  #include "qemu/osdep.h"
>  #include "qapi/error.h"
>  #include "qemu-common.h"
> +#include "qemu/error-report.h"
>  #include "sysemu/hostmem.h"
>  #include "sysemu/sysemu.h"
>  #include "qom/object_interfaces.h"
> @@ -34,6 +35,7 @@ struct HostMemoryBackendFile {
>      bool discard_data;
>      char *mem_path;
>      uint64_t align;
> +    bool is_pmem;
>  };
>  
>  static void
> @@ -59,7 +61,8 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error 
> **errp)
>          memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),
>                                   path,
>                                   backend->size, fb->align,
> -                                 backend->share ? RAM_SHARED : 0,
> +                                 (backend->share ? RAM_SHARED : 0) |
> +                                 (fb->is_pmem ? RAM_PMEM : 0),
>                                   fb->mem_path, errp);
>          g_free(path);
>      }
> @@ -131,6 +134,37 @@ static void file_memory_backend_set_align(Object *o, 
> Visitor *v,
>      error_propagate(errp, local_err);  }
>  
> +static bool file_memory_backend_get_pmem(Object *o, Error **errp) {
> +    return MEMORY_BACKEND_FILE(o)->is_pmem; }
> +
> +static void file_memory_backend_set_pmem(Object *o, bool value, Error 
> +**errp) {
> +    HostMemoryBackend *backend = MEMORY_BACKEND(o);
> +    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
> +
> +    if (host_memory_backend_mr_inited(backend)) {
> +        error_setg(errp, "cannot change property 'pmem' of %s '%s'",
> +                   object_get_typename(o),
> +                   object_get_canonical_path_component(o));
> +        return;
> +    }
> +
> +#ifndef CONFIG_LIBPMEM
> +    if (value) {
> +        error_report("Lack of libpmem support while setting the 'pmem=on'"
> +                     " of %s '%s'. We can not ensure the persistence of it"
> +                     " without libpmem support, this may cause serious"
> +                     " problems." , object_get_typename(o),
> +                     object_get_canonical_path_component(o));
> +        exit(1);
> +    }
> +#endif
> +
> +    fb->is_pmem = value;
> +}
> +
>  static void file_backend_unparent(Object *obj)  {
>      HostMemoryBackend *backend = MEMORY_BACKEND(obj); @@ -162,6 
> +196,9 @@ file_backend_class_init(ObjectClass *oc, void *data)
>          file_memory_backend_get_align,
>          file_memory_backend_set_align,
>          NULL, NULL, &error_abort);
> +    object_class_property_add_bool(oc, "pmem",
> +        file_memory_backend_get_pmem, file_memory_backend_set_pmem,
> +        &error_abort);
>  }
>  
>  static void file_backend_instance_finalize(Object *o) diff --git 
> a/docs/nvdimm.txt b/docs/nvdimm.txt index 8b48fb4..2f7d348 100644
> --- a/docs/nvdimm.txt
> +++ b/docs/nvdimm.txt
> @@ -180,3 +180,21 @@ supports CPU Cache Flush and Memory Controller Flush on 
> Power Loss, etc.
>  
>  For a complete list of the flags available and for more detailed 
> descriptions,  please consult the ACPI spec.
> +
> +guest software that this vNVDIMM device contains a region that cannot 
> +accept persistent writes. In result, for example, the guest Linux 
> +NVDIMM driver, marks such vNVDIMM device as read-only.
> +
> +If the vNVDIMM backend is on the host persistent memory that can be 
> +accessed in SNIA NVM Programming Model [1] (e.g., Intel NVDIMM), it's 
> +suggested to set the 'pmem' option of memory-backend-file to 'on'. 
> +When 'pmem=on' and QEMU is built with libpmem [2] support (configured 
> +with --enable-libpmem), QEMU will take necessary operations to 
> +guarantee the persistence of its own writes to the vNVDIMM backend 
> +(e.g., in vNVDIMM label emulation and live migration).
will libpmem guarantee data persistence even if backend's file is not on 
persistent memory?


> +
> +References
> +----------
> +
> +[1] SNIA NVM Programming Model: 
> +https://www.snia.org/sites/default/files/technical_work/final/NVMProg
> +rammingModel_v1.2.pdf
> +[2] PMDK: http://pmem.io/pmdk/
> diff --git a/exec.c b/exec.c
> index 8e079df..c42483e 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2077,6 +2077,9 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, 
> MemoryRegion *mr,
>      Error *local_err = NULL;
>      int64_t file_size;
>  
> +    /* Just support these ram flags by now. */
> +    assert(ram_flags == 0 || (ram_flags & (RAM_SHARED | RAM_PMEM)));
> +
>      if (xen_enabled()) {
>          error_setg(errp, "-mem-path not supported with Xen");
>          return NULL;
> @@ -4007,6 +4010,11 @@ err:
>      return ret;
>  }
>  
> +bool ramblock_is_pmem(RAMBlock *rb)
> +{
> +    return rb->flags & RAM_PMEM;
> +}
> +
>  #endif
>  
>  void page_size_init(void)
> @@ -4105,3 +4113,4 @@ void mtree_print_dispatch(fprintf_function mon, 
> void *f,  }
>  
>  #endif
> +
> diff --git a/include/exec/memory.h b/include/exec/memory.h index 
> 3769c06..7dd43b0 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -122,6 +122,9 @@ typedef struct IOMMUNotifier IOMMUNotifier;
>  /* RAM can be migrated */
>  #define RAM_MIGRATABLE (1 << 4)
>  
> +/* RAM is a persistent kind memory */ #define RAM_PMEM (1 << 5)
> +
>  static inline void iommu_notifier_init(IOMMUNotifier *n, IOMMUNotify fn,
>                                         IOMMUNotifierFlag flags,
>                                         hwaddr start, hwaddr end) @@ 
> -613,6 +616,7 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
>   *         (getpagesize()) will be used.
>   * @ram_flags: Memory region features:
>   *             - RAM_SHARED: memory must be mmaped with the MAP_SHARED flag
> + *             - RAM_PMEM: the memory is persistent memory
>   *             Other bits are ignored now.
>   * @path: the path in which to allocate the RAM.
>   * @errp: pointer to Error*, to store an error if it happens.
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h index 
> 5545cf3..3c65643 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -70,6 +70,8 @@ static inline unsigned long int 
> ramblock_recv_bitmap_offset(void *host_addr,
>      return host_addr_offset >> TARGET_PAGE_BITS;  }
>  
> +bool ramblock_is_pmem(RAMBlock *rb);
> +
>  long qemu_getrampagesize(void);
>  unsigned long last_ram_page(void);
>  
> @@ -84,6 +86,7 @@ unsigned long last_ram_page(void);
>   *  @ram_flags: specify the properties of the ram block, which can be one
>   *              or bit-or of following values
>   *              - RAM_SHARED: mmap the backing file or device with MAP_SHARED
> + *              - RAM_PMEM: the backend @mem_path or @fd is persistent memory
>   *              Other bits are ignored.
>   *  @mem_path or @fd: specify the backing file or device
>   *  @errp: pointer to Error*, to store an error if it happens diff 
> --git a/qemu-options.hx b/qemu-options.hx index c0d3951..006ca44 
> 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -4045,6 +4045,13 @@ requires an alignment different than the 
> default one used by QEMU, eg  the device DAX /dev/dax0.0 requires 2M 
> alignment rather than 4K. In  such cases, users can specify the required 
> alignment via this option.
>  
> +The @option{pmem} option specifies whether the backing file specified 
> +by @option{mem-path} is on the persistent memory that can be accessed 
> +using the SNIA NVM programming model (e.g. Intel NVDIMM).
> +If @option{pmem}, 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).
> +
>  @item -object 
> memory-backend-ram,address@hidden,address@hidden|off},address@hidden|off},sh
> address@hidden|off},address@hidden|off},address@hidden,address@hidden
> {host-nodes},address@hidden|preferred|bind|interleave}
>  
>  Creates a memory backend object, which can be used to back the guest RAM.




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