Applications in Linux guest that use device-dax never trigger flush that can be trapped by KVM/QEMU. Meanwhile, if the host backend is not device-dax, QEMU cannot guarantee the persistence of guest writes. Before solving this flushing problem, QEMU should warn users if the host backend is not device-dax.
Signed-off-by: Haozhong Zhang <haozhong.zh...@intel.com> Message-id: capcyv4hv2-zw8smcrtd0p_86kgr3dhovne+6t5sy2u7wxg3...@mail.gmail.com --- Cc: "Michael S. Tsirkin" <m...@redhat.com> Cc: Igor Mammedov <imamm...@redhat.com> Cc: Xiao Guangrong <guangrong.x...@gmail.com> Cc: Stefan Hajnoczi <stefa...@gmail.com> Cc: Dan Williams <dan.j.willi...@intel.com> --- Resend because the wrong maintainer email address was used. --- hw/mem/nvdimm.c | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) diff --git a/hw/mem/nvdimm.c b/hw/mem/nvdimm.c index db896b0bb6..c7bb407f33 100644 --- a/hw/mem/nvdimm.c +++ b/hw/mem/nvdimm.c @@ -26,6 +26,7 @@ #include "qapi/error.h" #include "qapi/visitor.h" #include "hw/mem/nvdimm.h" +#include "qemu/error-report.h" static void nvdimm_get_label_size(Object *obj, Visitor *v, const char *name, void *opaque, Error **errp) @@ -78,12 +79,48 @@ static MemoryRegion *nvdimm_get_memory_region(PCDIMMDevice *dimm) return &nvdimm->nvdimm_mr; } +static void nvdimm_check_dax(HostMemoryBackend *hostmem) +{ + char *mem_path = + object_property_get_str(OBJECT(hostmem), "mem-path", NULL); + char *dev_name = NULL, *sysfs_path = NULL; + bool is_dax = false; + + if (!mem_path) { + goto out; + } + + if (!g_str_has_prefix(mem_path, "/dev/dax")) { + goto out; + } + + dev_name = mem_path + strlen("/dev/"); + sysfs_path = g_strdup_printf("/sys/class/dax/%s", dev_name); + if (access(sysfs_path, F_OK)) { + goto out; + } + + is_dax = true; + + out: + if (!is_dax) { + error_report("warning: nvdimm backend %s is not DAX device, " + "unable to guarantee persistence of guest writes", + mem_path ?: "RAM"); + } + + g_free(sysfs_path); + g_free(mem_path); +} + static void nvdimm_realize(PCDIMMDevice *dimm, Error **errp) { MemoryRegion *mr = host_memory_backend_get_memory(dimm->hostmem, errp); NVDIMMDevice *nvdimm = NVDIMM(dimm); uint64_t align, pmem_size, size = memory_region_size(mr); + nvdimm_check_dax(dimm->hostmem); + align = memory_region_get_alignment(mr); pmem_size = size - nvdimm->label_size; -- 2.11.0