Commit 98376843 authored by Haozhong Zhang's avatar Haozhong Zhang Committed by Eduardo Habkost
Browse files

hostmem-file: add "align" option 



When mmap(2) the backend files, QEMU uses the host page size
(getpagesize(2)) by default as the alignment of mapping address.
However, some backends may require alignments different than the page
size. For example, mmap a device DAX (e.g., /dev/dax0.0) on Linux
kernel 4.13 to an address, which is 4K-aligned but not 2M-aligned,
fails with a kernel message like

[617494.969768] dax dax0.0: qemu-system-x86: dax_mmap: fail, unaligned vma (0x7fa37c579000 - 0x7fa43c579000, 0x1fffff)

Because there is no common approach to get such alignment requirement,
we add the 'align' option to 'memory-backend-file', so that users or
management utils, which have enough knowledge about the backend, can
specify a proper alignment via this option.

Signed-off-by: default avatarHaozhong Zhang <haozhong.zhang@intel.com>
Message-Id: <20171211072806.2812-2-haozhong.zhang@intel.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
[ehabkost: fixed typo, fixed error_setg() format string]
Signed-off-by: default avatarEduardo Habkost <ehabkost@redhat.com>
parent 1e2bdd2e

backends/hostmem-file.c

+40 −1
Original line number Diff line number Diff line
@@ -34,6 +34,7 @@ struct HostMemoryBackendFile { 
    bool share;

    bool discard_data;

    char *mem_path;

    uint64_t align;

};



static void
@@ -58,7 +59,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) 
        path = object_get_canonical_path(OBJECT(backend));

        memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),

                                 path,

                                 backend->size, fb->share,

                                 backend->size, fb->align, fb->share,

                                 fb->mem_path, errp);

        g_free(path);

    }
@@ -115,6 +116,40 @@ static void file_memory_backend_set_discard_data(Object *o, bool value, 
    MEMORY_BACKEND_FILE(o)->discard_data = value;

}



static void file_memory_backend_get_align(Object *o, Visitor *v,

                                          const char *name, void *opaque,

                                          Error **errp)

{

    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);

    uint64_t val = fb->align;



    visit_type_size(v, name, &val, errp);

}



static void file_memory_backend_set_align(Object *o, Visitor *v,

                                          const char *name, void *opaque,

                                          Error **errp)

{

    HostMemoryBackend *backend = MEMORY_BACKEND(o);

    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);

    Error *local_err = NULL;

    uint64_t val;



    if (host_memory_backend_mr_inited(backend)) {

        error_setg(&local_err, "cannot change property value");

        goto out;

    }



    visit_type_size(v, name, &val, &local_err);

    if (local_err) {

        goto out;

    }

    fb->align = val;



 out:

    error_propagate(errp, local_err);

}



static void file_backend_unparent(Object *obj)

{

    HostMemoryBackend *backend = MEMORY_BACKEND(obj);
@@ -145,6 +180,10 @@ file_backend_class_init(ObjectClass *oc, void *data) 
    object_class_property_add_str(oc, "mem-path",

        get_mem_path, set_mem_path,

        &error_abort);

    object_class_property_add(oc, "align", "int",

        file_memory_backend_get_align,

        file_memory_backend_set_align,

        NULL, NULL, &error_abort);

}



static void file_backend_instance_finalize(Object *o)

docs/nvdimm.txt

+16 −0
Original line number Diff line number Diff line
@@ -122,3 +122,19 @@ Note: 
     M >= size of RAM devices +

          size of statically plugged vNVDIMM devices +

          size of hotplugged vNVDIMM devices



Alignment

---------



QEMU uses mmap(2) to maps vNVDIMM backends and aligns the mapping

address to the page size (getpagesize(2)) by default. However, some

types of backends may require an alignment different than the page

size. In that case, QEMU v2.12.0 and later provide 'align' option to

memory-backend-file to allow users to specify the proper alignment.



For example, device dax require the 2 MB alignment, so we can use

following QEMU command line options to use it (/dev/dax0.0) as the

backend of vNVDIMM:



 -object memory-backend-file,id=mem1,share=on,mem-path=/dev/dax0.0,size=4G,align=2M

 -device nvdimm,id=nvdimm1,memdev=mem1

exec.c

+7 −1
Original line number Diff line number Diff line
@@ -1612,7 +1612,13 @@ static void *file_ram_alloc(RAMBlock *block, 
    void *area;



    block->page_size = qemu_fd_getpagesize(fd);

    block->mr->align = block->page_size;

    if (block->mr->align % block->page_size) {

        error_setg(errp, "alignment 0x%" PRIx64

                   " must be multiples of page size 0x%zx",

                   block->mr->align, block->page_size);

        return NULL;

    }

    block->mr->align = MAX(block->page_size, block->mr->align);

#if defined(__s390x__)

    if (kvm_enabled()) {

        block->mr->align = MAX(block->mr->align, QEMU_VMALLOC_ALIGN);

include/exec/memory.h

+3 −0
Original line number Diff line number Diff line
@@ -465,6 +465,8 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr, 
 * @name: Region name, becomes part of RAMBlock name used in migration stream

 *        must be unique within any device

 * @size: size of the region.

 * @align: alignment of the region base address; if 0, the default alignment

 *         (getpagesize()) will be used.

 * @share: %true if memory must be mmaped with the MAP_SHARED flag

 * @path: the path in which to allocate the RAM.

 * @errp: pointer to Error*, to store an error if it happens.
@@ -476,6 +478,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr, 
                                      struct Object *owner,

                                      const char *name,

                                      uint64_t size,

                                      uint64_t align,

                                      bool share,

                                      const char *path,

                                      Error **errp);

memory.c

+2 −0
Original line number Diff line number Diff line
@@ -1570,6 +1570,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr, 
                                      struct Object *owner,

                                      const char *name,

                                      uint64_t size,

                                      uint64_t align,

                                      bool share,

                                      const char *path,

                                      Error **errp)
@@ -1578,6 +1579,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr, 
    mr->ram = true;

    mr->terminates = true;

    mr->destructor = memory_region_destructor_ram;

    mr->align = align;

    mr->ram_block = qemu_ram_alloc_from_file(size, mr, share, path, errp);

    mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;

}