On 11/27/17 23:07 -0200, Eduardo Habkost wrote:
> On Mon, Nov 27, 2017 at 12:35:15PM +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>
>
> The new option needs to be documented on qemu-options.hx.
will add in the next version.
Thanks,
Haozhong
>
> Except for that, the patch looks good to me.
>
>
> > ---
> > 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
> >
>
> --
> Eduardo
