Re: [PATCH v12 16/19] multi-process: Synchronize remote memory

[Jag Raman]

> On Dec 8, 2020, at 8:57 AM, Marc-André Lureau <marcandre.lureau@gmail.com> 
> wrote:
> 
> Hi
> 
> On Wed, Dec 2, 2020 at 12:23 AM Jagannathan Raman <jag.raman@oracle.com> 
> wrote:
> Add memory-listener object which is used to keep the view of the RAM
> in sync between QEMU and remote process.
> A MemoryListener is registered for system-memory AddressSpace. The
> listener sends SYNC_SYSMEM message to the remote process when memory
> listener commits the changes to memory, the remote process receives
> the message and processes it in the handler for SYNC_SYSMEM message.
> 
> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  include/hw/remote/memory-sync.h |  27 ++++++
>  include/hw/remote/proxy.h       |   2 +
>  hw/remote/memory-sync.c         | 210 
> ++++++++++++++++++++++++++++++++++++++++
>  hw/remote/message.c             |   5 +
>  hw/remote/proxy.c               |   6 ++
>  MAINTAINERS                     |   2 +
>  hw/remote/meson.build           |   1 +
>  7 files changed, 253 insertions(+)
>  create mode 100644 include/hw/remote/memory-sync.h
>  create mode 100644 hw/remote/memory-sync.c
> 
> diff --git a/include/hw/remote/memory-sync.h b/include/hw/remote/memory-sync.h
> new file mode 100644
> index 0000000..785f76a
> --- /dev/null
> +++ b/include/hw/remote/memory-sync.h
> @@ -0,0 +1,27 @@
> +/*
> + * Copyright © 2018, 2020 Oracle and/or its affiliates.
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + *
> + */
> +
> +#ifndef MEMORY_SYNC_H
> +#define MEMORY_SYNC_H
> +
> +#include "exec/memory.h"
> +#include "io/channel.h"
> +
> +typedef struct RemoteMemSync {
> +    MemoryListener listener;
> +
> +    int n_mr_sections;
> +    MemoryRegionSection *mr_sections;
> +
> +    QIOChannel *ioc;
> +} RemoteMemSync;
> +
> +void configure_memory_sync(RemoteMemSync *sync, QIOChannel *ioc);
> +void deconfigure_memory_sync(RemoteMemSync *sync);
> 
> RemoteMemSync vs MemorySync, and function with _memory_sync suffixes...
> Naming things is hard, but trying to be consistent generally helps.
> 
> My understanding is that this is a proxy-dev helper to handle memory 
> listening and sending SYNC_SYSMEM.
> 
> I would thus suggest naming it ProxyMemoryListener. It could eventually be 
> folded in proxy.c
> 
> Please try to be consistent with header naming, structure naming, type, 
> functions and enum prefixes etc.
> 
> proxy_memory_listener isn't that long imho.
> 
> +
> +#endif
> diff --git a/include/hw/remote/proxy.h b/include/hw/remote/proxy.h
> index e29c61b..a687b7d 100644
> --- a/include/hw/remote/proxy.h
> +++ b/include/hw/remote/proxy.h
> @@ -11,6 +11,7 @@
> 
>  #include "hw/pci/pci.h"
>  #include "io/channel.h"
> +#include "hw/remote/memory-sync.h"
> 
>  #define TYPE_PCI_PROXY_DEV "x-pci-proxy-dev"
> 
> @@ -40,6 +41,7 @@ struct PCIProxyDev {
>      QemuMutex io_mutex;
>      QIOChannel *ioc;
>      Error *migration_blocker;
> +    RemoteMemSync sync;
>      ProxyMemoryRegion region[PCI_NUM_REGIONS];
>  };
> 
> diff --git a/hw/remote/memory-sync.c b/hw/remote/memory-sync.c
> new file mode 100644
> index 0000000..2365e69
> --- /dev/null
> +++ b/hw/remote/memory-sync.c
> @@ -0,0 +1,210 @@
> +/*
> + * Copyright © 2018, 2020 Oracle and/or its affiliates.
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + *
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qemu-common.h"
> +
> +#include "qemu/compiler.h"
> +#include "qemu/int128.h"
> +#include "qemu/range.h"
> +#include "exec/memory.h"
> +#include "exec/cpu-common.h"
> +#include "cpu.h"
> +#include "exec/ram_addr.h"
> +#include "exec/address-spaces.h"
> +#include "hw/remote/mpqemu-link.h"
> +#include "hw/remote/memory-sync.h"
> +
> +static void proxy_ml_begin(MemoryListener *listener)
> 
> I suggest to rename begin -> reset 
> 
> +{
> +    RemoteMemSync *sync = container_of(listener, RemoteMemSync, listener);
> +    int mrs;
> +
> +    for (mrs = 0; mrs < sync->n_mr_sections; mrs++) {
> +        memory_region_unref(sync->mr_sections[mrs].mr);
> +    }
> +
> +    g_free(sync->mr_sections);
> +    sync->mr_sections = NULL;
> +    sync->n_mr_sections = 0;
> +}
> +
> +static int get_fd_from_hostaddr(uint64_t host, ram_addr_t *offset)
> 
> This function is very similar to vhost_user_get_mr_data(). That suggests we 
> could factor the code.
> 
> Perhaps a new memory_region_from_host_full(), or extend 
> memory_region_from_host() with an extra optional "int *fd" argument.
>  
> +{
> +    MemoryRegion *mr;
> +    ram_addr_t off;
> +
> +    /**
> +     * Assumes that the host address is a valid address as it's
> +     * coming from the MemoryListener system. In the case host
> +     * address is not valid, the following call would return
> +     * the default subregion of "system_memory" region, and
> +     * not NULL. So it's not possible to check for NULL here.
> +     */
> +    mr = memory_region_from_host((void *)(uintptr_t)host, &off);
> +
> +    if (offset) {
> +        *offset = off;
> +    }
> +
> +    return memory_region_get_fd(mr);
> +}
> +
> +static bool proxy_mrs_can_merge(uint64_t host, uint64_t prev_host, size_t 
> size)
> +{
> 
> This seems similar to vhost_user_can_merge(). 
> 
> +    bool merge;
> +    int fd1, fd2;
> +
> +    fd1 = get_fd_from_hostaddr(host, NULL);
> +
> +    fd2 = get_fd_from_hostaddr(prev_host, NULL);
> +
> +    merge = (fd1 == fd2);
> 
> This could be written in a simpler manner, ex:
> 
> if (get_fd_from_hostaddr(host, NULL) != get_fd_from_hostaddr(prev_host, NULL))
>   return false
> 
> +
> +    merge &= ((prev_host + size) == host);
> 
> That check could be done early on before doing the more expensive 
> memory_region_from_host() calls
> 
> +
> +    return merge;
> +}
> +
> +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);
> +
> +    prev_sec = sync->mr_sections + (sync->n_mr_sections - 1);
> +    uint64_t prev_gpa_start = prev_sec->offset_within_address_space;
> +    uint64_t prev_size = int128_get64(prev_sec->size);
> +    uint64_t prev_gpa_end   = range_get_last(prev_gpa_start, prev_size);
> +    uint64_t prev_host_start =
> +        (uintptr_t)memory_region_get_ram_ptr(prev_sec->mr) +
> +        prev_sec->offset_within_region;
> +    uint64_t prev_host_end = range_get_last(prev_host_start, prev_size);
> +
> +    if (mrs_gpa <= (prev_gpa_end + 1)) {
> +        g_assert(mrs_gpa > prev_gpa_start);
> +
> +        if ((section->mr == prev_sec->mr) &&
> +            proxy_mrs_can_merge(mrs_host, prev_host_start,
> +                                (mrs_gpa - prev_gpa_start))) {
> +            uint64_t max_end = MAX(prev_host_end, mrs_host + mrs_size);
> +            merged = true;
> +            prev_sec->offset_within_address_space =
> +                MIN(prev_gpa_start, mrs_gpa);
> +            prev_sec->offset_within_region =
> +                MIN(prev_host_start, mrs_host) -
> +                (uintptr_t)memory_region_get_ram_ptr(prev_sec->mr);
> +            prev_sec->size = int128_make64(max_end - MIN(prev_host_start,
> +                                                         mrs_host));
> +        }
> +    }
> +
> +    return merged;
> +}
> +
> +static void proxy_ml_region_addnop(MemoryListener *listener,
> +                                   MemoryRegionSection *section)
> +{
> +    RemoteMemSync *sync = container_of(listener, RemoteMemSync, listener);
> +
> +    if (!(memory_region_is_ram(section->mr) &&
> +          !memory_region_is_rom(section->mr))) {
> +        return;
> 
> A bit clearer in vhost.c:
> if (memory_region_is_ram(mr) && !memory_region_is_rom(mr)) {
>  
> +    }
> +
> +    if (try_merge(sync, section)) {
> +        return;
> +    }
> +
> +    ++sync->n_mr_sections;
> +    sync->mr_sections = g_renew(MemoryRegionSection, sync->mr_sections,
> +                                sync->n_mr_sections);
> +    sync->mr_sections[sync->n_mr_sections - 1] = *section;
> +    sync->mr_sections[sync->n_mr_sections - 1].fv = NULL;
> +    memory_region_ref(section->mr);
> +}
> +
> +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;
> +    Error *local_err = NULL;
> +
> +    memset(&msg, 0, sizeof(MPQemuMsg));
> +
> +    msg.cmd = SYNC_SYSMEM;
> +    msg.num_fds = sync->n_mr_sections;
> +    msg.size = sizeof(SyncSysmemMsg);
> +    if (msg.num_fds > REMOTE_MAX_FDS) {
> +        error_report("Number of fds is more than %d", REMOTE_MAX_FDS);
> +        return;
> +    }
> +
> +    for (region = 0; region < sync->n_mr_sections; region++) {
> +        section = &sync->mr_sections[region];
> +        msg.data.sync_sysmem.gpas[region] =
> +            section->offset_within_address_space;
> +        msg.data.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.data.sync_sysmem.offsets[region] = offset;
> +    }
> +    mpqemu_msg_send(&msg, sync->ioc, &local_err);
> +    if (local_err) {
> +        error_report("Error in sending command %d", msg.cmd);
> +    }
> +}
> 
> That whole complex code above duplicates much of the logic in vhost.c. Can we 
> try to factorize it instead?

Hi Marc-Andre,

Thank you for sharing your feedback!

Would it be alright if we addressed this item alone in a separate patch in the 
future? Since
this refactoring affects vhost code, we’re wondering it would be better to 
address it in a
future patch to help with any regression analysis in the future.

Thank you!
—
Jag

> 
> +
> +void deconfigure_memory_sync(RemoteMemSync *sync)
> +{
> +    memory_listener_unregister(&sync->listener);
> +
> +    proxy_ml_begin(&sync->listener);
> +}
> +
> +void configure_memory_sync(RemoteMemSync *sync, QIOChannel *ioc)
> +{
> +    sync->n_mr_sections = 0;
> +    sync->mr_sections = NULL;
> +
> +    sync->ioc = ioc;
> +
> +    sync->listener.begin = proxy_ml_begin;
> +    sync->listener.commit = proxy_ml_commit;
> +    sync->listener.region_add = proxy_ml_region_addnop;
> +    sync->listener.region_nop = proxy_ml_region_addnop;
> +    sync->listener.priority = 10;
> +
> +    memory_listener_register(&sync->listener, &address_space_memory);
> +}
> diff --git a/hw/remote/message.c b/hw/remote/message.c
> index 0f3e38a..454fd2d 100644
> --- a/hw/remote/message.c
> +++ b/hw/remote/message.c
> @@ -17,6 +17,7 @@
>  #include "sysemu/runstate.h"
>  #include "hw/pci/pci.h"
>  #include "exec/memattrs.h"
> +#include "hw/remote/memory.h"
> 
>  static void process_config_write(QIOChannel *ioc, PCIDevice *dev,
>                                   MPQemuMsg *msg);
> @@ -64,6 +65,10 @@ void coroutine_fn mpqemu_remote_msg_loop_co(void *data)
>          case BAR_READ:
>              process_bar_read(com->ioc, &msg, &local_err);
>              break;
> +        case SYNC_SYSMEM:
> +            remote_sysmem_reconfig(&msg, &local_err);
> +            break;
> +
>          default:
>              error_setg(&local_err,
>                         "Unknown command (%d) received for device %s 
> (pid=%d)",
> diff --git a/hw/remote/proxy.c b/hw/remote/proxy.c
> index 039347d..0f2d1aa 100644
> --- a/hw/remote/proxy.c
> +++ b/hw/remote/proxy.c
> @@ -18,6 +18,8 @@
>  #include "migration/blocker.h"
>  #include "hw/remote/mpqemu-link.h"
>  #include "qemu/error-report.h"
> +#include "hw/remote/memory-sync.h"
> +#include "qom/object.h"
> 
>  static void proxy_set_socket(PCIProxyDev *pdev, int fd, Error **errp)
>  {
> @@ -58,6 +60,8 @@ static void pci_proxy_dev_realize(PCIDevice *device, Error 
> **errp)
> 
>      qemu_mutex_init(&dev->io_mutex);
>      qio_channel_set_blocking(dev->ioc, true, NULL);
> +
> +    configure_memory_sync(&dev->sync, dev->ioc);
>  }
> 
>  static void pci_proxy_dev_exit(PCIDevice *pdev)
> @@ -69,6 +73,8 @@ static void pci_proxy_dev_exit(PCIDevice *pdev)
>      migrate_del_blocker(dev->migration_blocker);
> 
>      error_free(dev->migration_blocker);
> +
> +    deconfigure_memory_sync(&dev->sync);
>  }
> 
>  static int config_op_send(PCIProxyDev *pdev, uint32_t addr, uint32_t *val,
> diff --git a/MAINTAINERS b/MAINTAINERS
> index ebd1d1d..5d78b78 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3150,6 +3150,8 @@ F: include/hw/remote/memory.h
>  F: hw/remote/memory.c
>  F: hw/remote/proxy.c
>  F: include/hw/remote/proxy.h
> +F: hw/remote/memory-sync.c
> +F: include/hw/remote/memory-sync.h
> 
>  Build and test automation
>  -------------------------
> diff --git a/hw/remote/meson.build b/hw/remote/meson.build
> index 569cd20..7d434a5 100644
> --- a/hw/remote/meson.build
> +++ b/hw/remote/meson.build
> @@ -7,5 +7,6 @@ remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: 
> files('remote-obj.c'))
>  remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('proxy.c'))
> 
>  specific_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('memory.c'))
> +specific_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('memory-sync.c'))
> 
>  softmmu_ss.add_all(when: 'CONFIG_MULTIPROCESS', if_true: remote_ss)
> -- 
> 1.8.3.1
> 
> 
> 
> -- 
> Marc-André Lureau