On 15.06.22 16:51, Steve Sistare wrote:
> A memory-backend-ram or a memory-backend-memfd block with the RAM_SHARED
> flag set is not migrated when migrate_ignore_shared() is true, but this
> is wrong, because it has no named backing store, and its contents will be
> lost. Define a new flag RAM_ANON to distinguish this case. Cpr will also
> test this flag, for similar reasons.
>
> Signed-off-by: Steve Sistare <steven.sist...@oracle.com>
> ---
> backends/hostmem-epc.c | 2 +-
> backends/hostmem-memfd.c | 1 +
> backends/hostmem-ram.c | 1 +
> include/exec/memory.h | 3 +++
> include/exec/ram_addr.h | 1 +
> migration/ram.c | 3 ++-
> softmmu/physmem.c | 12 +++++++++---
> 7 files changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/backends/hostmem-epc.c b/backends/hostmem-epc.c
> index 037292d..cb06255 100644
> --- a/backends/hostmem-epc.c
> +++ b/backends/hostmem-epc.c
> @@ -37,7 +37,7 @@ sgx_epc_backend_memory_alloc(HostMemoryBackend *backend,
> Error **errp)
> }
>
> name = object_get_canonical_path(OBJECT(backend));
> - ram_flags = (backend->share ? RAM_SHARED : 0) | RAM_PROTECTED;
> + ram_flags = (backend->share ? RAM_SHARED : 0) | RAM_PROTECTED | MAP_ANON;
I'm pretty sure that doesn't compile. -> RAM_ANON
> memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend),
> name, backend->size, ram_flags,
> fd, 0, errp);
> diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
> index 3fc85c3..c9d8001 100644
> --- a/backends/hostmem-memfd.c
> +++ b/backends/hostmem-memfd.c
> @@ -55,6 +55,7 @@ memfd_backend_memory_alloc(HostMemoryBackend *backend,
> Error **errp)
> name = host_memory_backend_get_name(backend);
> ram_flags = backend->share ? RAM_SHARED : 0;
> ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
> + ram_flags |= RAM_ANON;
> memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend), name,
> backend->size, ram_flags, fd, 0, errp);
> g_free(name);
> diff --git a/backends/hostmem-ram.c b/backends/hostmem-ram.c
> index b8e55cd..5e80149 100644
> --- a/backends/hostmem-ram.c
> +++ b/backends/hostmem-ram.c
> @@ -30,6 +30,7 @@ ram_backend_memory_alloc(HostMemoryBackend *backend, Error
> **errp)
> name = host_memory_backend_get_name(backend);
> ram_flags = backend->share ? RAM_SHARED : 0;
> ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
> + ram_flags |= RAM_ANON;
> memory_region_init_ram_flags_nomigrate(&backend->mr, OBJECT(backend),
> name,
> backend->size, ram_flags, errp);
> g_free(name);
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index f1c1945..0daddd7 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -203,6 +203,9 @@ typedef struct IOMMUTLBEvent {
> /* RAM that isn't accessible through normal means. */
> #define RAM_PROTECTED (1 << 8)
>
> +/* RAM has no name outside the qemu process. */
> +#define RAM_ANON (1 << 9)
That name is a bit misleading because it mangles anonymous memory with
an anonymous file, which doesn't provide anonymous memory in "kernel
speak". Please find a better name, some idea below ...
I think what you actual want to know is: is this from a real file,
instead of from an anonymous file or anonymous memory. A real file can
be re-opened and remapped after closing QEMU. Further, you need
MAP_SHARED semantics.
/* RAM maps a real file instead of an anonymous file or no file/fd. */
#define RAM_REAL_FILE (1 << 9)
bool ramblock_maps_real_file(RAMBlock *rb)
{
return rb->flags & RAM_REAL_FILE;
}
Maybe we can come up with a better name for "real file".
Set the flag from applicable callsites. When setting the flag
internally, assert that we don't have a fd -- that cannot possibly make
sense.
At applicable callsites check for ramblock_maps_real_file() and that
it's actually a shared mapping. If not, it cannot be preserved by
restarting QEMU (easily, there might be ways for memfd involving other
processes).
Make sense?
--
Thanks,
David / dhildenb
