| Message ID | b5b9f9c6bba07879fb43f3c6f496c69867ae3716.1717584048.git.mprivozn@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | backends/hostmem: Report more errors on failures | expand |
This patch has been successfully tested. Try to allocate some 2M hugepages in the host, then boot up a VM with the memory size unaligned and backed by a file, QEMU prompts the following message: qemu-system-x86_64: backend 'memory-backend-file' memory size must be multiple of 2 MiB Tested-by: Mario Casquero <mcasquer@redhat.com> On Wed, Jun 5, 2024 at 12:45 PM Michal Privoznik <mprivozn@redhat.com> wrote: > > 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> > --- > backends/hostmem.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/backends/hostmem.c b/backends/hostmem.c > index 012a8c190f..4d6c69fe4d 100644 > --- 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 > @@ -337,6 +338,7 @@ 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) { > @@ -348,6 +350,14 @@ 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 (!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)) { > -- > 2.44.1 > >
diff --git a/backends/hostmem.c b/backends/hostmem.c index 012a8c190f..4d6c69fe4d 100644 --- 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 @@ -337,6 +338,7 @@ 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) { @@ -348,6 +350,14 @@ 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 (!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)) {
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> --- backends/hostmem.c | 10 ++++++++++ 1 file changed, 10 insertions(+)