backends/hostmem-file.c | 40 +++++++++++++++++++++++++++++++++++++++- hw/virtio/vhost-user.c | 1 + include/exec/memory.h | 2 ++ include/exec/ram_addr.h | 3 ++- include/exec/ramblock.h | 1 + qapi/qom.json | 5 +++++ qemu-options.hx | 6 +++++- softmmu/memory.c | 3 ++- softmmu/physmem.c | 17 ++++++++++++----- 9 files changed, 69 insertions(+), 9 deletions(-)
Add an option for hostmem-file to start the memory object at an offset
into the target file. This is useful if multiple memory objects reside
inside the same target file, such as a device node.
In particular, it's useful to map guest memory directly into /dev/mem
for experimentation.
To make this work consistently, also fix up all places in QEMU that
expect fd offsets to be 0.
Signed-off-by: Alexander Graf <graf@amazon.com>
---
v1 -> v2:
- add qom documentation
- propagate offset into truncate, size and alignment checks
v2 -> v3:
- failed attempt at fixing typo
v3 -> v4:
- fix typo
v4 -> v5:
- improve qom doc comment
- account for fd_offset in more places
---
backends/hostmem-file.c | 40 +++++++++++++++++++++++++++++++++++++++-
hw/virtio/vhost-user.c | 1 +
include/exec/memory.h | 2 ++
include/exec/ram_addr.h | 3 ++-
include/exec/ramblock.h | 1 +
qapi/qom.json | 5 +++++
qemu-options.hx | 6 +++++-
softmmu/memory.c | 3 ++-
softmmu/physmem.c | 17 ++++++++++++-----
9 files changed, 69 insertions(+), 9 deletions(-)
diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index 25141283c4..38ea65bec5 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -27,6 +27,7 @@ struct HostMemoryBackendFile {
char *mem_path;
uint64_t align;
+ uint64_t offset;
bool discard_data;
bool is_pmem;
bool readonly;
@@ -58,7 +59,8 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
ram_flags |= fb->is_pmem ? RAM_PMEM : 0;
memory_region_init_ram_from_file(&backend->mr, OBJECT(backend), name,
backend->size, fb->align, ram_flags,
- fb->mem_path, fb->readonly, errp);
+ fb->mem_path, fb->offset, fb->readonly,
+ errp);
g_free(name);
#endif
}
@@ -125,6 +127,36 @@ static void file_memory_backend_set_align(Object *o, Visitor *v,
fb->align = val;
}
+static void file_memory_backend_get_offset(Object *o, Visitor *v,
+ const char *name, void *opaque,
+ Error **errp)
+{
+ HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
+ uint64_t val = fb->offset;
+
+ visit_type_size(v, name, &val, errp);
+}
+
+static void file_memory_backend_set_offset(Object *o, Visitor *v,
+ const char *name, void *opaque,
+ Error **errp)
+{
+ HostMemoryBackend *backend = MEMORY_BACKEND(o);
+ HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
+ uint64_t val;
+
+ if (host_memory_backend_mr_inited(backend)) {
+ error_setg(errp, "cannot change property '%s' of %s", name,
+ object_get_typename(o));
+ return;
+ }
+
+ if (!visit_type_size(v, name, &val, errp)) {
+ return;
+ }
+ fb->offset = val;
+}
+
#ifdef CONFIG_LIBPMEM
static bool file_memory_backend_get_pmem(Object *o, Error **errp)
{
@@ -197,6 +229,12 @@ file_backend_class_init(ObjectClass *oc, void *data)
file_memory_backend_get_align,
file_memory_backend_set_align,
NULL, NULL);
+ object_class_property_add(oc, "offset", "int",
+ file_memory_backend_get_offset,
+ file_memory_backend_set_offset,
+ NULL, NULL);
+ object_class_property_set_description(oc, "offset",
+ "Offset into the target file (ex: 1G)");
#ifdef CONFIG_LIBPMEM
object_class_property_add_bool(oc, "pmem",
file_memory_backend_get_pmem, file_memory_backend_set_pmem);
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index e5285df4ba..39dc803b03 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -483,6 +483,7 @@ static MemoryRegion *vhost_user_get_mr_data(uint64_t addr, ram_addr_t *offset,
assert((uintptr_t)addr == addr);
mr = memory_region_from_host((void *)(uintptr_t)addr, offset);
*fd = memory_region_get_fd(mr);
+ *offset += mr->ram_block->fd_offset;
return mr;
}
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 15ade918ba..3b7295fbe2 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -1318,6 +1318,7 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
* @ram_flags: RamBlock flags. Supported flags: RAM_SHARED, RAM_PMEM,
* RAM_NORESERVE,
* @path: the path in which to allocate the RAM.
+ * @offset: offset within the file referenced by path
* @readonly: true to open @path for reading, false for read/write.
* @errp: pointer to Error*, to store an error if it happens.
*
@@ -1331,6 +1332,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
uint64_t align,
uint32_t ram_flags,
const char *path,
+ ram_addr_t offset,
bool readonly,
Error **errp);
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index f4fb6a2111..90a8269290 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -110,6 +110,7 @@ long qemu_maxrampagesize(void);
* @ram_flags: RamBlock flags. Supported flags: RAM_SHARED, RAM_PMEM,
* RAM_NORESERVE.
* @mem_path or @fd: specify the backing file or device
+ * @offset: Offset into target file
* @readonly: true to open @path for reading, false for read/write.
* @errp: pointer to Error*, to store an error if it happens
*
@@ -119,7 +120,7 @@ long qemu_maxrampagesize(void);
*/
RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
uint32_t ram_flags, const char *mem_path,
- bool readonly, Error **errp);
+ off_t offset, bool readonly, Error **errp);
RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
uint32_t ram_flags, int fd, off_t offset,
bool readonly, Error **errp);
diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h
index adc03df59c..69c6a53902 100644
--- a/include/exec/ramblock.h
+++ b/include/exec/ramblock.h
@@ -40,6 +40,7 @@ struct RAMBlock {
QLIST_ENTRY(RAMBlock) next;
QLIST_HEAD(, RAMBlockNotifier) ramblock_notifiers;
int fd;
+ uint64_t fd_offset;
size_t page_size;
/* dirty bitmap used during migration */
unsigned long *bmap;
diff --git a/qapi/qom.json b/qapi/qom.json
index a877b879b9..f740f74be3 100644
--- a/qapi/qom.json
+++ b/qapi/qom.json
@@ -635,6 +635,10 @@
# specify the required alignment via this option.
# 0 selects a default alignment (currently the page size). (default: 0)
#
+# @offset: the offset into the target file that the region starts at. You can
+# use this option to back multiple regions with a single file. Must be
+# a multiple of the page size. (default: 0) (since 8.1)
+#
# @discard-data: if true, the file contents can be destroyed when QEMU exits,
# to avoid unnecessarily flushing data to the backing file. Note
# that ``discard-data`` is only an optimization, and QEMU might
@@ -655,6 +659,7 @@
{ 'struct': 'MemoryBackendFileProperties',
'base': 'MemoryBackendProperties',
'data': { '*align': 'size',
+ '*offset': 'size',
'*discard-data': 'bool',
'mem-path': 'str',
'*pmem': { 'type': 'bool', 'if': 'CONFIG_LIBPMEM' },
diff --git a/qemu-options.hx b/qemu-options.hx
index 59bdf67a2c..fb4eb81af4 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4859,7 +4859,7 @@ SRST
they are specified. Note that the 'id' property must be set. These
objects are placed in the '/objects' path.
- ``-object memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align,readonly=on|off``
+ ``-object memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align,offset=offset,readonly=on|off``
Creates a memory file backend object, which can be used to back
the guest RAM with huge pages.
@@ -4929,6 +4929,10 @@ SRST
such cases, users can specify the required alignment via this
option.
+ The ``offset`` option specifies the offset into the target file
+ that the region starts at. You can use this parameter to back
+ multiple regions with a single file.
+
The ``pmem`` option specifies whether the backing file specified
by ``mem-path`` is in host persistent memory that can be
accessed using the SNIA NVM programming model (e.g. Intel
diff --git a/softmmu/memory.c b/softmmu/memory.c
index 5305aca7ca..9f620085a0 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -1601,6 +1601,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
uint64_t align,
uint32_t ram_flags,
const char *path,
+ ram_addr_t offset,
bool readonly,
Error **errp)
{
@@ -1612,7 +1613,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
mr->destructor = memory_region_destructor_ram;
mr->align = align;
mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path,
- readonly, &err);
+ offset, readonly, &err);
if (err) {
mr->size = int128_zero();
object_unparent(OBJECT(mr));
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 0e0182d9f2..32460d7a3a 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -1369,6 +1369,11 @@ static void *file_ram_alloc(RAMBlock *block,
error_setg(errp, "alignment 0x%" PRIx64
" must be a power of two", block->mr->align);
return NULL;
+ } else if (offset % block->page_size) {
+ error_setg(errp, "offset 0x%" PRIx64
+ " must be multiples of page size 0x%zx",
+ offset, block->page_size);
+ return NULL;
}
block->mr->align = MAX(block->page_size, block->mr->align);
#if defined(__s390x__)
@@ -1400,7 +1405,7 @@ static void *file_ram_alloc(RAMBlock *block,
* those labels. Therefore, extending the non-empty backend file
* is disabled as well.
*/
- if (truncate && ftruncate(fd, memory)) {
+ if (truncate && ftruncate(fd, offset + memory)) {
perror("ftruncate");
}
@@ -1416,6 +1421,7 @@ static void *file_ram_alloc(RAMBlock *block,
}
block->fd = fd;
+ block->fd_offset = offset;
return area;
}
#endif
@@ -1889,7 +1895,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
size = HOST_PAGE_ALIGN(size);
file_size = get_file_size(fd);
- if (file_size > 0 && file_size < size) {
+ if (file_size > offset && file_size < (offset + size)) {
error_setg(errp, "backing store size 0x%" PRIx64
" does not match 'size' option 0x" RAM_ADDR_FMT,
file_size, size);
@@ -1929,7 +1935,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
uint32_t ram_flags, const char *mem_path,
- bool readonly, Error **errp)
+ off_t offset, bool readonly, Error **errp)
{
int fd;
bool created;
@@ -1941,7 +1947,8 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
return NULL;
}
- block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, 0, readonly, errp);
+ block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, offset, readonly,
+ errp);
if (!block) {
if (created) {
unlink(mem_path);
@@ -2075,7 +2082,7 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
flags |= block->flags & RAM_NORESERVE ? MAP_NORESERVE : 0;
if (block->fd >= 0) {
area = mmap(vaddr, length, PROT_READ | PROT_WRITE,
- flags, block->fd, offset);
+ flags, block->fd, offset + block->fd_offset);
} else {
flags |= MAP_ANONYMOUS;
area = mmap(vaddr, length, PROT_READ | PROT_WRITE,
--
2.39.2
Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879On 04.04.23 00:14, Alexander Graf wrote: > Add an option for hostmem-file to start the memory object at an offset > into the target file. This is useful if multiple memory objects reside > inside the same target file, such as a device node. > > In particular, it's useful to map guest memory directly into /dev/mem > for experimentation. > > To make this work consistently, also fix up all places in QEMU that > expect fd offsets to be 0. > > Signed-off-by: Alexander Graf <graf@amazon.com> > > --- > > v1 -> v2: > > - add qom documentation > - propagate offset into truncate, size and alignment checks > > v2 -> v3: > > - failed attempt at fixing typo > > v3 -> v4: > > - fix typo > > v4 -> v5: > > - improve qom doc comment > - account for fd_offset in more places > --- I queued this as is to https://github.com/davidhildenbrand/qemu.git mem-next I might send this upstream soonish (nothing else is really pending). Thanks! -- Thanks, David / dhildenb
On Mon, Apr 03, 2023 at 10:14:21PM +0000, Alexander Graf wrote:
> Add an option for hostmem-file to start the memory object at an offset
> into the target file. This is useful if multiple memory objects reside
> inside the same target file, such as a device node.
>
> In particular, it's useful to map guest memory directly into /dev/mem
> for experimentation.
>
> To make this work consistently, also fix up all places in QEMU that
> expect fd offsets to be 0.
>
> Signed-off-by: Alexander Graf <graf@amazon.com>
Acked-by: Peter Xu <peterx@redhat.com>
I also agree it'll be nicer to split the fix into separate patch, though.
The only affected part IIUC is multi-process QEMU since 6.0.0. Copying the
maintainers too so they'll be aware.
Corresponds to the tag:
Fixes: ed5d001916 ("multi-process: setup memory manager for remote device")
--
Peter Xu
On 04.04.23 16:36, Peter Xu wrote:
> On Mon, Apr 03, 2023 at 10:14:21PM +0000, Alexander Graf wrote:
>> Add an option for hostmem-file to start the memory object at an offset
>> into the target file. This is useful if multiple memory objects reside
>> inside the same target file, such as a device node.
>>
>> In particular, it's useful to map guest memory directly into /dev/mem
>> for experimentation.
>>
>> To make this work consistently, also fix up all places in QEMU that
>> expect fd offsets to be 0.
>>
>> Signed-off-by: Alexander Graf <graf@amazon.com>
>
> Acked-by: Peter Xu <peterx@redhat.com>
>
> I also agree it'll be nicer to split the fix into separate patch, though.
> The only affected part IIUC is multi-process QEMU since 6.0.0. Copying the
> maintainers too so they'll be aware.
>
> Corresponds to the tag:
>
> Fixes: ed5d001916 ("multi-process: setup memory manager for remote device")
>
If there are no options on splitting out the fix, I'll route this via my
tree.
--
Thanks,
David / dhildenb
On Wed, 5 Apr 2023 15:58:31 +0200
David Hildenbrand <david@redhat.com> wrote:
> On 04.04.23 16:36, Peter Xu wrote:
> > On Mon, Apr 03, 2023 at 10:14:21PM +0000, Alexander Graf wrote:
> >> Add an option for hostmem-file to start the memory object at an offset
> >> into the target file. This is useful if multiple memory objects reside
> >> inside the same target file, such as a device node.
> >>
> >> In particular, it's useful to map guest memory directly into /dev/mem
> >> for experimentation.
> >>
> >> To make this work consistently, also fix up all places in QEMU that
> >> expect fd offsets to be 0.
> >>
> >> Signed-off-by: Alexander Graf <graf@amazon.com>
> >
> > Acked-by: Peter Xu <peterx@redhat.com>
> >
> > I also agree it'll be nicer to split the fix into separate patch, though.
> > The only affected part IIUC is multi-process QEMU since 6.0.0. Copying the
> > maintainers too so they'll be aware.
> >
> > Corresponds to the tag:
> >
> > Fixes: ed5d001916 ("multi-process: setup memory manager for remote device")
> >
>
> If there are no options on splitting out the fix, I'll route this via my
> tree.
Having fixes as separate prep patch is much more preferable.
Another question is if we should also check that provided
offset honors 'align' option?
On 11.04.23 13:46, Igor Mammedov wrote:
> On Wed, 5 Apr 2023 15:58:31 +0200
> David Hildenbrand <david@redhat.com> wrote:
>
>> On 04.04.23 16:36, Peter Xu wrote:
>>> On Mon, Apr 03, 2023 at 10:14:21PM +0000, Alexander Graf wrote:
>>>> Add an option for hostmem-file to start the memory object at an offset
>>>> into the target file. This is useful if multiple memory objects reside
>>>> inside the same target file, such as a device node.
>>>>
>>>> In particular, it's useful to map guest memory directly into /dev/mem
>>>> for experimentation.
>>>>
>>>> To make this work consistently, also fix up all places in QEMU that
>>>> expect fd offsets to be 0.
>>>>
>>>> Signed-off-by: Alexander Graf <graf@amazon.com>
>>>
>>> Acked-by: Peter Xu <peterx@redhat.com>
>>>
>>> I also agree it'll be nicer to split the fix into separate patch, though.
>>> The only affected part IIUC is multi-process QEMU since 6.0.0. Copying the
>>> maintainers too so they'll be aware.
>>>
>>> Corresponds to the tag:
>>>
>>> Fixes: ed5d001916 ("multi-process: setup memory manager for remote device")
>>>
>>
>> If there are no options on splitting out the fix, I'll route this via my
>> tree.
>
> Having fixes as separate prep patch is much more preferable.
>
Right. Question is if it's really worth it. (it's quite a corner cases I
guess ...)
> Another question is if we should also check that provided
> offset honors 'align' option?
Good point, but I wonder if it's a real requirement (IOW, what would go
wrong)? The important part seems to be that the offset is aligned to the
underlying page size.
I'll be on vacation until 2. Mai, planning on picking it up by then to
send it upstream.
--
Thanks,
David / dhildenb
Alexander Graf <graf@amazon.com> writes:
> Add an option for hostmem-file to start the memory object at an offset
> into the target file. This is useful if multiple memory objects reside
> inside the same target file, such as a device node.
>
> In particular, it's useful to map guest memory directly into /dev/mem
> for experimentation.
>
> To make this work consistently, also fix up all places in QEMU that
> expect fd offsets to be 0.
>
> Signed-off-by: Alexander Graf <graf@amazon.com>
[...]
> diff --git a/qapi/qom.json b/qapi/qom.json
> index a877b879b9..f740f74be3 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -635,6 +635,10 @@
> # specify the required alignment via this option.
> # 0 selects a default alignment (currently the page size). (default: 0)
> #
> +# @offset: the offset into the target file that the region starts at. You can
> +# use this option to back multiple regions with a single file. Must be
> +# a multiple of the page size. (default: 0) (since 8.1)
> +#
> # @discard-data: if true, the file contents can be destroyed when QEMU exits,
> # to avoid unnecessarily flushing data to the backing file. Note
> # that ``discard-data`` is only an optimization, and QEMU might
> @@ -655,6 +659,7 @@
> { 'struct': 'MemoryBackendFileProperties',
> 'base': 'MemoryBackendProperties',
> 'data': { '*align': 'size',
> + '*offset': 'size',
> '*discard-data': 'bool',
> 'mem-path': 'str',
> '*pmem': { 'type': 'bool', 'if': 'CONFIG_LIBPMEM' },
Acked-by: Markus Armbruster <armbru@redhat.com>
[...]
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