Re: [PATCH v5 16/50] multi-process: Synchronize remote memory

[Jag Raman <jag.raman@oracle.com>]

On 3/4/2020 6:53 AM, Dr. David Alan Gilbert wrote:
> * 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.
>>
>> TODO: No need to create object for remote memory listener.
>>
>> 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>
>> ---
>>   Makefile.target                |   3 +
>>   hw/proxy/memory-sync.c         | 212 +++++++++++++++++++++++++++++++++++++++++
>>   hw/proxy/qemu-proxy.c          |   5 +
>>   include/hw/proxy/memory-sync.h |  37 +++++++
>>   include/hw/proxy/qemu-proxy.h  |   5 +
>>   remote/remote-main.c           |  11 +++
>>   6 files changed, 273 insertions(+)
>>   create mode 100644 hw/proxy/memory-sync.c
>>   create mode 100644 include/hw/proxy/memory-sync.h
>>
>> diff --git a/Makefile.target b/Makefile.target
>> index cfd36c1..271d883 100644
>> --- a/Makefile.target
>> +++ b/Makefile.target
>> @@ -127,6 +127,9 @@ obj-$(CONFIG_TCG) += fpu/softfloat.o
>>   obj-y += target/$(TARGET_BASE_ARCH)/
>>   obj-y += disas.o
>>   obj-$(call notempty,$(TARGET_XML_FILES)) += gdbstub-xml.o
>> +ifeq ($(TARGET_NAME)-$(CONFIG_MPQEMU)-$(CONFIG_USER_ONLY), x86_64-y-)
>> +obj-$(CONFIG_MPQEMU) += hw/proxy/memory-sync.o
>> +endif
>>   LIBS := $(libs_cpu) $(LIBS)
>>   
>>   obj-$(CONFIG_PLUGIN) += plugins/
>> diff --git a/hw/proxy/memory-sync.c b/hw/proxy/memory-sync.c
>> new file mode 100644
>> index 0000000..3edbb19
>> --- /dev/null
>> +++ b/hw/proxy/memory-sync.c
>> @@ -0,0 +1,212 @@
>> +/*
>> + * 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 <sys/types.h>
>> +#include <stdio.h>
>> +#include <string.h>
>> +
>> +#include "qemu/osdep.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 "io/mpqemu-link.h"
>> +#include "hw/proxy/memory-sync.h"
>> +
>> +static const TypeInfo remote_mem_sync_type_info = {
>> +    .name          = TYPE_MEMORY_LISTENER,
>> +    .parent        = TYPE_OBJECT,
>> +    .instance_size = sizeof(RemoteMemSync),
>> +};
>> +
>> +static void remote_mem_sync_register_types(void)
>> +{
>> +    type_register_static(&remote_mem_sync_type_info);
>> +}
>> +
>> +type_init(remote_mem_sync_register_types)
>> +
>> +static void proxy_ml_begin(MemoryListener *listener)
>> +{
>> +    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)
>> +{
>> +    MemoryRegion *mr;
>> +    ram_addr_t off;
>> +
>> +    mr = memory_region_from_host((void *)(uintptr_t)host, &off);
> 
> Do you need to just check we found an 'mr' ?

OK, we'll add this check.

> 
>> +    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)
>> +{
>> +    bool merge;
>> +    int fd1, fd2;
>> +
>> +    fd1 = get_fd_from_hostaddr(host, NULL);
>> +
>> +    fd2 = get_fd_from_hostaddr(prev_host, NULL);
>> +
>> +    merge = (fd1 == fd2);
>> +
>> +    merge &= ((prev_host + size) == host);
> 
> It's interesting; I think the vhost code checks that the two mr's are
> the same where you are checking for the same underlying fd - but I think
> that's OK.
> (I wonder if we need to check offset's within the fd's match up when
> they're merged - since you added that offset feature in an earlier
> patch?
> That would also need checking in vhost_region_add_section)

If the fds are the same, and the subsequent check ((prev_host + size) ==
host) passes, then I believe the offsets would match as well.

> 
>> +    return merge;
>> +}
>> +
>> +static void proxy_ml_region_addnop(MemoryListener *listener,
>> +                                   MemoryRegionSection *section)
>> +{
>> +    RemoteMemSync *sync = container_of(listener, RemoteMemSync, listener);
>> +    bool need_add = true;
>> +    uint64_t mrs_size, mrs_gpa, mrs_page;
>> +    uintptr_t mrs_host;
>> +    RAMBlock *mrs_rb;
>> +    MemoryRegionSection *prev_sec;
>> +
>> +    if (!(memory_region_is_ram(section->mr) &&
>> +          !memory_region_is_rom(section->mr))) {
>> +        return;
>> +    }
>> +
>> +    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;
>> +    }
>> +
>> +    mrs_host = mrs_host & ~(mrs_page - 1);
>> +    mrs_gpa = mrs_gpa & ~(mrs_page - 1);
>> +    mrs_size = ROUND_UP(mrs_size, mrs_page);
> 
> OK, just note the more complex code in vhost_region_add_section for page
> aligning regions that are needed for postcopy; I think that would be the
> same if you wanted to do postcopy with remote processes.

Since mmap requires the addresses to be aligned with a page boundry, we
added these checks. We are essentially doing the same with alignage as
compared with vhost user. So we should be compliant with postcopy I
believe.

> 
>> +    if (sync->n_mr_sections) {
>> +        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)) {
>> +            if (mrs_gpa < prev_gpa_start) {
>> +                assert(0);
>> +            }
> 
> g_assert(mrs_gpa < prev_gpa_start);

Thank you, we'll update the above check with the version you proposed.

> 
> 
>> +            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);
>> +                need_add = false;
>> +                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));
>> +            }
>> +        }
>> +    }
>> +
>> +    if (need_add) {
>> +        ++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);
>> +    }
> 
> I'd add some tracing in this function; it's a nightmare to debug when it
> does something unexpected.

Thank you, we'll add the tracing.

> 
>> +}
>> +
>> +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];
>> +        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);
> 
> Since you already have section.mr you cna use memory_region_get_fd.

OK.

Thank you!
--
Jag

> 
>> +        msg.data1.sync_sysmem.offsets[region] = offset;
>> +    }
>> +    mpqemu_msg_send(&msg, sync->mpqemu_link->com);
>> +}
>> +
>> +void deconfigure_memory_sync(RemoteMemSync *sync)
>> +{
>> +    memory_listener_unregister(&sync->listener);
>> +}
>> +
>> +/*
>> + * TODO: Memory Sync need not be instantianted once per every proxy device.
>> + *       All remote devices are going to get the exact same updates at the
>> + *       same time. It therefore makes sense to have a broadcast model.
>> + *
>> + *       Broadcast model would involve running the MemorySync object in a
>> + *       thread. MemorySync would contain a list of mpqemu-link objects
>> + *       that need notification. proxy_ml_commit() could send the same
>> + *       message to all the links at the same time.
>> + */
>> +void configure_memory_sync(RemoteMemSync *sync, MPQemuLinkState *mpqemu_link)
>> +{
>> +    sync->n_mr_sections = 0;
>> +    sync->mr_sections = NULL;
>> +
>> +    sync->mpqemu_link = mpqemu_link;
>> +
>> +    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/proxy/qemu-proxy.c b/hw/proxy/qemu-proxy.c
>> index b17d9bb..d3a9d38 100644
>> --- a/hw/proxy/qemu-proxy.c
>> +++ b/hw/proxy/qemu-proxy.c
>> @@ -16,6 +16,8 @@
>>   #include "qapi/qmp/qjson.h"
>>   #include "qapi/qmp/qstring.h"
>>   #include "hw/proxy/qemu-proxy.h"
>> +#include "hw/proxy/memory-sync.h"
>> +#include "qom/object.h"
>>   
>>   static void pci_proxy_dev_realize(PCIDevice *dev, Error **errp);
>>   
>> @@ -243,6 +245,8 @@ static void init_proxy(PCIDevice *dev, char *command, char *exec_name,
>>   
>>       mpqemu_init_channel(pdev->mpqemu_link, &pdev->mpqemu_link->com,
>>                           pdev->socket);
>> +
>> +    configure_memory_sync(pdev->sync, pdev->mpqemu_link);
>>   }
>>   
>>   static void pci_proxy_dev_realize(PCIDevice *device, Error **errp)
>> @@ -261,6 +265,7 @@ static void pci_proxy_dev_realize(PCIDevice *device, Error **errp)
>>       dev->set_proxy_sock = set_proxy_sock;
>>       dev->get_proxy_sock = get_proxy_sock;
>>       dev->init_proxy = init_proxy;
>> +    dev->sync = REMOTE_MEM_SYNC(object_new(TYPE_MEMORY_LISTENER));
>>   }
>>   
>>   static void send_bar_access_msg(PCIProxyDev *dev, MemoryRegion *mr,
>> diff --git a/include/hw/proxy/memory-sync.h b/include/hw/proxy/memory-sync.h
>> new file mode 100644
>> index 0000000..d8329c9
>> --- /dev/null
>> +++ b/include/hw/proxy/memory-sync.h
>> @@ -0,0 +1,37 @@
>> +/*
>> + * 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 <sys/types.h>
>> +
>> +#include "qemu/osdep.h"
>> +#include "qom/object.h"
>> +#include "exec/memory.h"
>> +#include "io/mpqemu-link.h"
>> +
>> +#define TYPE_MEMORY_LISTENER "memory-listener"
>> +#define REMOTE_MEM_SYNC(obj) \
>> +            OBJECT_CHECK(RemoteMemSync, (obj), TYPE_MEMORY_LISTENER)
>> +
>> +typedef struct RemoteMemSync {
>> +    Object obj;
>> +
>> +    MemoryListener listener;
>> +
>> +    int n_mr_sections;
>> +    MemoryRegionSection *mr_sections;
>> +
>> +    MPQemuLinkState *mpqemu_link;
>> +} RemoteMemSync;
>> +
>> +void configure_memory_sync(RemoteMemSync *sync, MPQemuLinkState *mpqemu_link);
>> +void deconfigure_memory_sync(RemoteMemSync *sync);
>> +
>> +#endif
>> diff --git a/include/hw/proxy/qemu-proxy.h b/include/hw/proxy/qemu-proxy.h
>> index 44e370e..c93ffe3 100644
>> --- a/include/hw/proxy/qemu-proxy.h
>> +++ b/include/hw/proxy/qemu-proxy.h
>> @@ -10,6 +10,7 @@
>>   #define QEMU_PROXY_H
>>   
>>   #include "io/mpqemu-link.h"
>> +#include "hw/proxy/memory-sync.h"
>>   
>>   #define TYPE_PCI_PROXY_DEV "pci-proxy-dev"
>>   
>> @@ -37,8 +38,12 @@ extern const MemoryRegionOps proxy_default_ops;
>>   struct PCIProxyDev {
>>       PCIDevice parent_dev;
>>   
>> +    int n_mr_sections;
>> +    MemoryRegionSection *mr_sections;
>> +
>>       MPQemuLinkState *mpqemu_link;
>>   
>> +    RemoteMemSync *sync;
>>       pid_t remote_pid;
>>       int socket;
>>   
>> diff --git a/remote/remote-main.c b/remote/remote-main.c
>> index acd8daf..9512a3b 100644
>> --- a/remote/remote-main.c
>> +++ b/remote/remote-main.c
>> @@ -34,6 +34,7 @@
>>   #include "block/block.h"
>>   #include "exec/ramlist.h"
>>   #include "exec/memattrs.h"
>> +#include "exec/address-spaces.h"
>>   
>>   static MPQemuLinkState *mpqemu_link;
>>   PCIDevice *remote_pci_dev;
>> @@ -161,6 +162,16 @@ static void process_msg(GIOCondition cond, MPQemuChannel *chan)
>>               goto finalize_loop;
>>           }
>>           break;
>> +    case SYNC_SYSMEM:
>> +        /*
>> +         * TODO: ensure no active DMA is happening when
>> +         * sysmem is being updated
> 
> In practice this turns out to be hard!
> 
> Dave
> 
>> +         */
>> +        remote_sysmem_reconfig(msg, &err);
>> +        if (err) {
>> +            goto finalize_loop;
>> +        }
>> +        break;
>>       default:
>>           error_setg(&err, "Unknown command");
>>           goto finalize_loop;
>> -- 
>> 1.8.3.1
>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>