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On 11/27/17 12:35 +0800, Haozhong Zhang wrote:
> 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: Haozhong Zhang <haozhong.zh...@intel.com>
> ---
> backends/hostmem-file.c | 41 ++++++++++++++++++++++++++++++++++++++++-
> docs/nvdimm.txt | 16 ++++++++++++++++
> exec.c | 8 +++++++-
> include/exec/memory.h | 3 +++
> memory.c | 2 ++
> numa.c | 2 +-
> 6 files changed, 69 insertions(+), 3 deletions(-)
>
> diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
> index e44c319915..e319ec1ad8 100644
> --- a/backends/hostmem-file.c
> +++ b/backends/hostmem-file.c
> @@ -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)
> diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
> index 2d9f8c0e8c..21249dd062 100644
> --- a/docs/nvdimm.txt
> +++ b/docs/nvdimm.txt
> @@ -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
> diff --git a/exec.c b/exec.c
> index 03238a3449..90440efecd 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1600,7 +1600,13 @@ 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, "aligment 0x%" PRIx64
> + " must be multiples of page size 0x%" PRIx64,
> + 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);
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 5ed4042f87..a1be8b06d3 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -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);
> diff --git a/memory.c b/memory.c
> index e26e5a3b1d..2c80656e39 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -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;
> }
> diff --git a/numa.c b/numa.c
> index 7151b24d1c..b0fe22a60c 100644
> --- a/numa.c
> +++ b/numa.c
> @@ -551,7 +551,7 @@ static void allocate_system_memory_nonnuma(MemoryRegion
> *mr, Object *owner,
> if (mem_path) {
> #ifdef __linux__
> Error *err = NULL;
> - memory_region_init_ram_from_file(mr, owner, name, ram_size, false,
> + memory_region_init_ram_from_file(mr, owner, name, ram_size, 0, false,
> mem_path, &err);
> if (err) {
> error_report_err(err);
> --
> 2.14.1
>
