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backends/hostmem: Report error when memory size is unaligned

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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>
This commit is contained in:
Michal Privoznik 2024-06-05 12:44:58 +02:00 committed by Paolo Bonzini
parent 210b7b2b3c
commit 5d9a9a6170
5 changed files with 14 additions and 1 deletions
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1
backends/hostmem-epc.c
View file

@ -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,

1
backends/hostmem-file.c
View file

@ -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;

1
backends/hostmem-memfd.c
View file

@ -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;

10
backends/hostmem.c
View file

@ -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);

2
include/sysemu/hostmem.h
View file

@ -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);