backends/hostmem: Report error when memory size is unaligned

If memory-backend-{file,ram} has a size that's not aligned to
underlying page size it is not only wasteful, but also may lead
to hard to debug behaviour. For instance, in case
memory-backend-file and hugepages, madvise() and mbind() fail.
Rightfully so, page is the smallest unit they can work with. And
even though an error is reported, the root cause it not very
clear:

  qemu-system-x86_64: Couldn't set property 'dump' on 'memory-backend-file': Invalid argument

After this commit:

  qemu-system-x86_64: backend 'memory-backend-file' memory size must be multiple of 2 MiB

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Mario Casquero <mcasquer@redhat.com>
Message-ID: <b5b9f9c6bba07879fb43f3c6f496c69867ae3716.1717584048.git.mprivozn@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/backends/hostmem-epc.c b/backends/hostmem-epc.c
index 735e2e1cf84670c891ba4571f09ec44256e64f82..f58fcf00a10bb142eddf50dd1492f131a2ad489b 100644 (file)
--- a/backends/hostmem-epc.c
+++ b/backends/hostmem-epc.c
@@ -36,6 +36,7 @@ sgx_epc_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         return false;
     }
 
+    backend->aligned = true;
     name = object_get_canonical_path(OBJECT(backend));
     ram_flags = (backend->share ? RAM_SHARED : 0) | RAM_PROTECTED;
     return memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend), name,

diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index 3c69db794607391f954fcccaaad910343c3840a0..7e5072e33ef148213bae337b2c685e9b45edc261 100644 (file)
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -80,6 +80,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         g_assert_not_reached();
     }
 
+    backend->aligned = true;
     name = host_memory_backend_get_name(backend);
     ram_flags = backend->share ? RAM_SHARED : 0;
     ram_flags |= fb->readonly ? RAM_READONLY_FD : 0;

diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
index 745ead0034dc6e6987e5c2a2e7a575e16bab6b9f..6a3c89a12b24eed58b1619384bc07712fb4fef49 100644 (file)
--- a/backends/hostmem-memfd.c
+++ b/backends/hostmem-memfd.c
@@ -52,6 +52,7 @@ memfd_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         return false;
     }
 
+    backend->aligned = true;
     name = host_memory_backend_get_name(backend);
     ram_flags = backend->share ? RAM_SHARED : 0;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;

diff --git a/backends/hostmem.c b/backends/hostmem.c
index eb9682b4a856fefc850af17d0a7b98d952942d05..1edc0ede2a5d4680860d992f4419efb289b145b2 100644 (file)
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -20,6 +20,7 @@
 #include "qom/object_interfaces.h"
 #include "qemu/mmap-alloc.h"
 #include "qemu/madvise.h"
+#include "qemu/cutils.h"
 #include "hw/qdev-core.h"
 
 #ifdef CONFIG_NUMA
@@ -325,6 +326,7 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
     HostMemoryBackendClass *bc = MEMORY_BACKEND_GET_CLASS(uc);
     void *ptr;
     uint64_t sz;
+    size_t pagesize;
     bool async = !phase_check(PHASE_LATE_BACKENDS_CREATED);
 
     if (!bc->alloc) {
@@ -336,6 +338,14 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
 
     ptr = memory_region_get_ram_ptr(&backend->mr);
     sz = memory_region_size(&backend->mr);
+    pagesize = qemu_ram_pagesize(backend->mr.ram_block);
+
+    if (backend->aligned && !QEMU_IS_ALIGNED(sz, pagesize)) {
+        g_autofree char *pagesize_str = size_to_str(pagesize);
+        error_setg(errp, "backend '%s' memory size must be multiple of %s",
+                   object_get_typename(OBJECT(uc)), pagesize_str);
+        return;
+    }
 
     if (backend->merge) {
         qemu_madvise(ptr, sz, QEMU_MADV_MERGEABLE);

diff --git a/include/sysemu/hostmem.h b/include/sysemu/hostmem.h
index 04b884bf42a603bd825a70a8216f63d1f256b500..de47ae59e4b8a13e6252fe4161e6a35f7382bcb1 100644 (file)
--- a/include/sysemu/hostmem.h
+++ b/include/sysemu/hostmem.h
@@ -74,7 +74,7 @@ struct HostMemoryBackend {
     uint64_t size;
     bool merge, dump, use_canonical_path;
     bool prealloc, is_mapped, share, reserve;
-    bool guest_memfd;
+    bool guest_memfd, aligned;
     uint32_t prealloc_threads;
     ThreadContext *prealloc_context;
     DECLARE_BITMAP(host_nodes, MAX_NODES + 1);