Asahi Lina wrote: [..] > I don't think that's how it actually works, at least on arm64. > arch_wb_cache_pmem() calls dcache_clean_pop() which is either dc cvap or > dc cvac. Those are trapped by HCR_EL2<TPC>, and that is never set by KVM. > > There was some discussion of this here: > https://lore.kernel.org/all/20190702055937.3ffpwph7anvohmxu@US-160370MP2.local/ > > But I'm not sure that all really made sense then. > > msync() and fsync() should already provide persistence. Those end up > calling vfs_fsync_range(), which becomes a FUSE fsync(), which fsyncs > (or fdatasyncs) the whole file. What I'm not so sure is whether there > are any other codepaths that also need to provide those guarantees which > *don't* end up calling fsync on the VFS. For example, the manpages kind > of imply munmap() syncs, though as far as I can tell that's not actually > the case. If there are missing sync paths, then I think those might just > be broken right now... IIRC, from the pmem persistence dicussions, if userspace fails to call *sync then there is no obligation to flush on munmap() or close(). Some filesystems layer on those guarantees, but the behavior is implementation specific.
