Hi
On Wed, Jul 7, 2021 at 9:31 PM Steve Sistare <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>
>
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?)
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?
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
