Re: [PATCH v7 15/21] multi-process: Synchronize remote memory

[Stefan Hajnoczi]

On Sat, Jun 27, 2020 at 10:09:37AM -0700, elena.ufimtseva@oracle.com wrote:
> +static bool try_merge(RemoteMemSync *sync, MemoryRegionSection *section)
> +{
> +    uint64_t mrs_size, mrs_gpa, mrs_page;
> +    MemoryRegionSection *prev_sec;
> +    bool merged = false;
> +    uintptr_t mrs_host;
> +    RAMBlock *mrs_rb;
> +
> +    if (!sync->n_mr_sections) {
> +        return false;
> +    }
> +
> +    mrs_rb = section->mr->ram_block;
> +    mrs_page = (uint64_t)qemu_ram_pagesize(mrs_rb);
> +    mrs_size = int128_get64(section->size);
> +    mrs_gpa = section->offset_within_address_space;
> +    mrs_host = (uintptr_t)memory_region_get_ram_ptr(section->mr) +
> +               section->offset_within_region;
> +
> +    if (get_fd_from_hostaddr(mrs_host, NULL) < 0) {
> +        return true;
> +    }
> +
> +    mrs_host = mrs_host & ~(mrs_page - 1);
> +    mrs_gpa = mrs_gpa & ~(mrs_page - 1);
> +    mrs_size = ROUND_UP(mrs_size, mrs_page);
> +
> +    if (sync->n_mr_sections) {

The check is unnecessary because of the if statement above:

  if (!sync->n_mr_sections) {
     return false;
  }

> +static void proxy_ml_commit(MemoryListener *listener)
> +{
> +    RemoteMemSync *sync = container_of(listener, RemoteMemSync, listener);
> +    MPQemuMsg msg;
> +    MemoryRegionSection section;
> +    ram_addr_t offset;
> +    uintptr_t host_addr;
> +    int region;
> +
> +    memset(&msg, 0, sizeof(MPQemuMsg));
> +
> +    msg.cmd = SYNC_SYSMEM;
> +    msg.bytestream = 0;
> +    msg.num_fds = sync->n_mr_sections;
> +    msg.size = sizeof(msg.data1);
> +    assert(msg.num_fds <= REMOTE_MAX_FDS);
> +
> +    for (region = 0; region < sync->n_mr_sections; region++) {
> +        section = sync->mr_sections[region];

Why is section copied here? It's conventional to take a pointer to a
struct instead of copying its value.

> +        msg.data1.sync_sysmem.gpas[region] =
> +            section.offset_within_address_space;
> +        msg.data1.sync_sysmem.sizes[region] = int128_get64(section.size);
> +        host_addr = (uintptr_t)memory_region_get_ram_ptr(section.mr) +
> +                    section.offset_within_region;
> +        msg.fds[region] = get_fd_from_hostaddr(host_addr, &offset);
> +        msg.data1.sync_sysmem.offsets[region] = offset;
> +    }
> +    mpqemu_msg_send(&msg, sync->ioc);
> +}
> +
> +void deconfigure_memory_sync(RemoteMemSync *sync)
> +{

Missing proxy_ml_begin() call to free sync->mr_sections[] and unref
sections.

> +    memory_listener_unregister(&sync->listener);
> +}

This function isn't called. It's good practice to implement the object
lifecycle from the start.

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