On 7/8/2021 11:54 AM, Marc-André Lureau wrote: > On Thu, Jul 8, 2021 at 7:43 PM Marc-André Lureau <marcandre.lur...@gmail.com > <mailto:marcandre.lur...@gmail.com>> wrote: > > Hi > > On Wed, Jul 7, 2021 at 9:31 PM Steve Sistare <steven.sist...@oracle.com > <mailto:steven.sist...@oracle.com>> wrote: > > Provide the cprsave restart mode, which preserves the guest VM across > a > restart of the qemu process. After cprsave, the caller passes qemu > command-line arguments to cprexec, which directly exec's the new qemu > binary. The arguments must include -S so new qemu starts in a paused > state. > The caller resumes the guest by calling cprload. > > To use the restart mode, qemu must be started with the memfd-alloc > machine > option. The memfd's are saved to the environment and kept open > across exec, > after which they are found from the environment and re-mmap'd. Hence > guest > ram is preserved in place, albeit with new virtual addresses in the > qemu > process. > > The restart mode supports vfio devices in a subsequent patch. > > Signed-off-by: Steve Sistare <steven.sist...@oracle.com > <mailto:steven.sist...@oracle.com>> > > > What's the plan to make it work with -object memory-backend-memfd > -machine memory-backend? > (or memory-backend-file, I guess that should work?) > > > It seems to be addressed in some way in a later "hostmem-memfd: cpr support" > patch.
Correct, but in both cases you also need the memfd-alloc machine option so that misc small segments are preserved. For some discussion see: https://lore.kernel.org/qemu-devel/YKPEWicpOeh3yo5%2F@stefanha-x1.localdomain/ > Imho it's worth mentioning in the commit message, reorganize patches closer. OK. > And the checks be added anyway for unsupported configurations. The only-cpr-capable option in the next to last patch performs those checks. > There should be some extra checks before accepting cprexec() on a > misconfigured VM. > > --- > migration/cpr.c | 21 +++++++++++++++++++++ > softmmu/physmem.c | 6 +++++- > 2 files changed, 26 insertions(+), 1 deletion(-) > > diff --git a/migration/cpr.c b/migration/cpr.c > index c5bad8a..fb57dec 100644 > --- a/migration/cpr.c > +++ b/migration/cpr.c > @@ -29,6 +29,7 @@ > #include "sysemu/xen.h" > #include "hw/vfio/vfio-common.h" > #include "hw/virtio/vhost.h" > +#include "qemu/env.h" > > QEMUFile *qf_file_open(const char *path, int flags, int mode, > const char *name, Error **errp) > @@ -108,6 +109,26 @@ done: > return; > } > > +static int preserve_fd(const char *name, const char *val, void > *handle) > +{ > + qemu_clr_cloexec(atoi(val)); > + return 0; > +} > + > +void cprexec(strList *args, Error **errp) > +{ > + if (xen_enabled()) { > + error_setg(errp, "xen does not support cprexec"); > + return; > + } > + if (!runstate_check(RUN_STATE_SAVE_VM)) { > + error_setg(errp, "runstate is not save-vm"); > + return; > + } > + walkenv(FD_PREFIX, preserve_fd, 0); > > > I am not convinced that relying on environment variables here is the > best thing to do. > > + qemu_system_exec_request(args); > +} > + > void cprload(const char *file, Error **errp) > { > QEMUFile *f; > diff --git a/softmmu/physmem.c b/softmmu/physmem.c > index b149250..8a65ef7 100644 > --- a/softmmu/physmem.c > +++ b/softmmu/physmem.c > @@ -65,6 +65,7 @@ > #include "qemu/pmem.h" > > #include "qemu/memfd.h" > +#include "qemu/env.h" > #include "migration/vmstate.h" > > #include "qemu/range.h" > @@ -1986,7 +1987,7 @@ static void ram_block_add(RAMBlock *new_block, > Error **errp) > } else { > name = memory_region_name(new_block->mr); > if (ms->memfd_alloc) { > > > > - int mfd = -1; /* placeholder until next > patch */ > + int mfd = getenv_fd(name); > mr->align = QEMU_VMALLOC_ALIGN; > if (mfd < 0) { > mfd = qemu_memfd_create(name, maxlen + mr->align, > @@ -1994,7 +1995,9 @@ static void ram_block_add(RAMBlock *new_block, > Error **errp) > if (mfd < 0) { > return; > } > + setenv_fd(name, mfd); > } > + qemu_clr_cloexec(mfd); > > > Why clear it now, and on exec again? That's a bug, thanks. This should be qemu_set_cloexec(), so the mfd is closed for any misc fork/exec calls prior to cprexec. - Steve > new_block->flags |= RAM_SHARED; > addr = file_ram_alloc(new_block, maxlen, mfd, > false, false, 0, errp); > @@ -2246,6 +2249,7 @@ void qemu_ram_free(RAMBlock *block) > } > > qemu_mutex_lock_ramlist(); > + unsetenv_fd(memory_region_name(block->mr)); > QLIST_REMOVE_RCU(block, next); > ram_list.mru_block = NULL; > /* Write list before version */ > -- > 1.8.3.1 > > > > > -- > Marc-André Lureau > > > > -- > Marc-André Lureau
