On 11/21/2012 01:32 PM, Stefan Hajnoczi wrote:
> The data plane thread needs to map guest physical addresses to host
> pointers. Normally this is done with cpu_physical_memory_map() but the
> function assumes the global mutex is held. The data plane thread does
> not touch the global mutex and therefore needs a thread-safe memory
> mapping mechanism.
>
> Hostmem registers a MemoryListener similar to how vhost collects and
> pushes memory region information into the kernel. There is a
> fine-grained lock on the regions list which is held during lookup and
> when installing a new regions list.
>
> When the physical memory map changes the MemoryListener callbacks are
> invoked. They build up a new list of memory regions which is finally
> installed when the list has been completed.
>
> Note that this approach is not safe across memory hotplug because mapped
> pointers may still be in used across memory unplug. However, this is
> currently a problem for QEMU in general and needs to be addressed in the
> future.
>
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> ---
> hw/dataplane/Makefile.objs | 3 +
> hw/dataplane/hostmem.c | 165
> +++++++++++++++++++++++++++++++++++++++++++++
> hw/dataplane/hostmem.h | 52 ++++++++++++++
> 3 files changed, 220 insertions(+)
> create mode 100644 hw/dataplane/Makefile.objs
> create mode 100644 hw/dataplane/hostmem.c
> create mode 100644 hw/dataplane/hostmem.h
>
> diff --git a/hw/dataplane/Makefile.objs b/hw/dataplane/Makefile.objs
> new file mode 100644
> index 0000000..8c8dea1
> --- /dev/null
> +++ b/hw/dataplane/Makefile.objs
> @@ -0,0 +1,3 @@
> +ifeq ($(CONFIG_VIRTIO), y)
> +common-obj-$(CONFIG_VIRTIO_BLK_DATA_PLANE) += hostmem.o
> +endif
> diff --git a/hw/dataplane/hostmem.c b/hw/dataplane/hostmem.c
> new file mode 100644
> index 0000000..48aabf0
> --- /dev/null
> +++ b/hw/dataplane/hostmem.c
> @@ -0,0 +1,165 @@
> +/*
> + * Thread-safe guest to host memory mapping
> + *
> + * Copyright 2012 Red Hat, Inc. and/or its affiliates
> + *
> + * Authors:
> + * Stefan Hajnoczi <stefa...@redhat.com>
> + *
> + * 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 "exec-memory.h"
> +#include "hostmem.h"
> +
> +static int hostmem_lookup_cmp(const void *phys_, const void *region_)
> +{
> + hwaddr phys = *(const hwaddr *)phys_;
> + const HostmemRegion *region = region_;
> +
> + if (phys < region->guest_addr) {
> + return -1;
> + } else if (phys >= region->guest_addr + region->size) {
> + return 1;
> + } else {
> + return 0;
> + }
> +}
> +
> +/**
> + * Map guest physical address to host pointer
> + */
> +void *hostmem_lookup(Hostmem *hostmem, hwaddr phys, hwaddr len, bool
> is_write)
> +{
> + HostmemRegion *region;
> + void *host_addr = NULL;
> + hwaddr offset_within_region;
> +
> + qemu_mutex_lock(&hostmem->current_regions_lock);
> + region = bsearch(&phys, hostmem->current_regions,
> + hostmem->num_current_regions,
> + sizeof(hostmem->current_regions[0]),
> + hostmem_lookup_cmp);
> + if (!region) {
> + goto out;
> + }
> + if (is_write && region->readonly) {
> + goto out;
> + }
> + offset_within_region = phys - region->guest_addr;
> + if (offset_within_region + len <= region->size) {
> + host_addr = region->host_addr + offset_within_region;
> + }
> +out:
> + qemu_mutex_unlock(&hostmem->current_regions_lock);
> +
> + return host_addr;
> +}
> +
> +/**
> + * Install new regions list
> + */
> +static void hostmem_listener_commit(MemoryListener *listener)
> +{
> + Hostmem *hostmem = container_of(listener, Hostmem, listener);
> +
> + qemu_mutex_lock(&hostmem->current_regions_lock);
> + g_free(hostmem->current_regions);
> + hostmem->current_regions = hostmem->new_regions;
> + hostmem->num_current_regions = hostmem->num_new_regions;
> + qemu_mutex_unlock(&hostmem->current_regions_lock);
> +
> + /* Reset new regions list */
> + hostmem->new_regions = NULL;
> + hostmem->num_new_regions = 0;
> +}
> +
> +/**
> + * Add a MemoryRegionSection to the new regions list
> + */
> +static void hostmem_append_new_region(Hostmem *hostmem,
> + MemoryRegionSection *section)
> +{
> + void *ram_ptr = memory_region_get_ram_ptr(section->mr);
> + size_t num = hostmem->num_new_regions;
> + size_t new_size = (num + 1) * sizeof(hostmem->new_regions[0]);
> +
> + hostmem->new_regions = g_realloc(hostmem->new_regions, new_size);
> + hostmem->new_regions[num] = (HostmemRegion){
> + .host_addr = ram_ptr + section->offset_within_region,
> + .guest_addr = section->offset_within_address_space,
> + .size = section->size,
> + .readonly = section->readonly,
> + };
> + hostmem->num_new_regions++;
> +}
> +
> +static void hostmem_listener_append_region(MemoryListener *listener,
> + MemoryRegionSection *section)
> +{
> + Hostmem *hostmem = container_of(listener, Hostmem, listener);
> +
> + if (memory_region_is_ram(section->mr)) {
> + hostmem_append_new_region(hostmem, section);
> + }
> +}
> +
> +/* We don't implement most MemoryListener callbacks, use these nop stubs */
> +static void hostmem_listener_dummy(MemoryListener *listener)
> +{
> +}
> +
> +static void hostmem_listener_section_dummy(MemoryListener *listener,
> + MemoryRegionSection *section)
> +{
> +}
> +
> +static void hostmem_listener_eventfd_dummy(MemoryListener *listener,
> + MemoryRegionSection *section,
> + bool match_data, uint64_t data,
> + EventNotifier *e)
> +{
> +}
> +
> +static void hostmem_listener_coalesced_mmio_dummy(MemoryListener *listener,
> + MemoryRegionSection
> *section,
> + hwaddr addr, hwaddr len)
> +{
> +}
> +
> +void hostmem_init(Hostmem *hostmem)
> +{
> + memset(hostmem, 0, sizeof(*hostmem));
> +
> + hostmem->listener = (MemoryListener){
> + .begin = hostmem_listener_dummy,
> + .commit = hostmem_listener_commit,
> + .region_add = hostmem_listener_append_region,
> + .region_del = hostmem_listener_section_dummy,
> + .region_nop = hostmem_listener_append_region,
OK, more explicitly, I find it odd that append_region is a nop (unless
there's a new meaning of
"nop" I am unaware of). I would have expected the section_dummy function.
> + .log_start = hostmem_listener_section_dummy,
> + .log_stop = hostmem_listener_section_dummy,
> + .log_sync = hostmem_listener_section_dummy,
> + .log_global_start = hostmem_listener_dummy,
> + .log_global_stop = hostmem_listener_dummy,
> + .eventfd_add = hostmem_listener_eventfd_dummy,
> + .eventfd_del = hostmem_listener_eventfd_dummy,
> + .coalesced_mmio_add = hostmem_listener_coalesced_mmio_dummy,
> + .coalesced_mmio_del = hostmem_listener_coalesced_mmio_dummy,
> + .priority = 10,
> + };
>
-d
