Re: [PATCH v7 12/17] vfio-user: IOMMU support for remote device

[Jag Raman]

> On Apr 13, 2022, at 2:24 PM, Jag Raman <jag.raman@oracle.com> wrote:
> 
> 
> 
>> On Apr 13, 2022, at 10:25 AM, Igor Mammedov <imammedo@redhat.com> wrote:
>> 
>> On Fri, 25 Mar 2022 15:19:41 -0400
>> Jagannathan Raman <jag.raman@oracle.com> wrote:
>> 
>>> Assign separate address space for each device in the remote processes.
>>> 
>>> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
>>> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
>>> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
>>> ---
>>> include/hw/remote/iommu.h | 18 ++++++++
>>> hw/remote/iommu.c         | 95 +++++++++++++++++++++++++++++++++++++++
>>> MAINTAINERS               |  2 +
>>> hw/remote/meson.build     |  1 +
>>> 4 files changed, 116 insertions(+)
>>> create mode 100644 include/hw/remote/iommu.h
>>> create mode 100644 hw/remote/iommu.c
>>> 
>>> diff --git a/include/hw/remote/iommu.h b/include/hw/remote/iommu.h
>>> new file mode 100644
>>> index 0000000000..8f850400f1
>>> --- /dev/null
>>> +++ b/include/hw/remote/iommu.h
>>> @@ -0,0 +1,18 @@
>>> +/**
>>> + * Copyright © 2022 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 REMOTE_IOMMU_H
>>> +#define REMOTE_IOMMU_H
>>> +
>>> +#include "hw/pci/pci_bus.h"
>>> +
>>> +void remote_configure_iommu(PCIBus *pci_bus);
>>> +
>>> +void remote_iommu_del_device(PCIDevice *pci_dev);
>>> +
>>> +#endif
>>> diff --git a/hw/remote/iommu.c b/hw/remote/iommu.c
>>> new file mode 100644
>>> index 0000000000..13f329b45d
>>> --- /dev/null
>>> +++ b/hw/remote/iommu.c
>>> @@ -0,0 +1,95 @@
>>> +/**
>>> + * IOMMU for remote device
>>> + *
>>> + * Copyright © 2022 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 "hw/remote/iommu.h"
>>> +#include "hw/pci/pci_bus.h"
>>> +#include "hw/pci/pci.h"
>>> +#include "exec/memory.h"
>>> +#include "exec/address-spaces.h"
>>> +#include "trace.h"
>>> +
>>> +struct RemoteIommuElem {
>>> +    AddressSpace  as;
>>> +    MemoryRegion  mr;
>>> +};
>>> +
>>> +struct RemoteIommuTable {
>>> +    QemuMutex lock;
>>> +    GHashTable *elem_by_bdf;
>>> +} remote_iommu_table;
>>> +
>>> +#define INT2VOIDP(i) (void *)(uintptr_t)(i)
>>> +
>>> +static AddressSpace *remote_iommu_find_add_as(PCIBus *pci_bus,
>>> +                                              void *opaque, int devfn)
>>> +{
>>> +    struct RemoteIommuTable *iommu_table = opaque;
>>> +    struct RemoteIommuElem *elem = NULL;
>>> +    int pci_bdf = PCI_BUILD_BDF(pci_bus_num(pci_bus), devfn);
>>> +
>>> +    elem = g_hash_table_lookup(iommu_table->elem_by_bdf, 
>>> INT2VOIDP(pci_bdf));
>>> +
>>> +    if (!elem) {
>>> +        g_autofree char *mr_name = g_strdup_printf("vfu-ram-%d", pci_bdf);
>>> +        g_autofree char *as_name = g_strdup_printf("vfu-as-%d", pci_bdf);
>>> +
>>> +        elem = g_malloc0(sizeof(struct RemoteIommuElem));
>>> +
>>> +        memory_region_init(&elem->mr, NULL, mr_name, UINT64_MAX);
>> goes here:
>>  memory_region_do_init()
>>       if (!owner) {                                                          
>>   
>>           owner = container_get(qdev_get_machine(), "/unattached");          
>>   
>>       }  
>> 
>> then
>> 
>>> +        address_space_init(&elem->as, &elem->mr, as_name);
>>> +
>>> +        qemu_mutex_lock(&iommu_table->lock);
>>> +        g_hash_table_insert(iommu_table->elem_by_bdf, INT2VOIDP(pci_bdf), 
>>> elem);
>>> +        qemu_mutex_unlock(&iommu_table->lock);
>>> +    }
>>> +
>>> +    return &elem->as;
>>> +}
>>> +
>>> +static void remote_iommu_del_elem(gpointer data)
>>> +{
>>> +    struct RemoteIommuElem *elem = data;
>>> +
>>> +    g_assert(elem);
>>> +
>>> +    memory_region_unref(&elem->mr);
>> 
>> here we call
>>     object_unref(mr->owner); 
>> leaving dangling pointer in owner '(qdev_get_machine(), "/unattached")'
>> it doesn't look correct
>> 
>> I thought that memory_region_unref() should be always paired with 
>> memory_region_ref()
>> 
>> and looking at memory_region_init(...owner...) history it looks like
>> owner-less (NULL) regions are not meant to be deleted ever.
> 
> Hi Igor,
> 
> Thanks for the pointers about ref counters for MemoryRegions.
> 
> It makes sense - MemoryRegions are not QEMU Objects. So their
> owner’s ref counters are used instead. So the expectation is that
> when the owner is destroyed, the MemoryRegions initialized by them
> also get destroyed simultaneously.

Well, MemoryRegions are indeed QEMU objects -
"memory_region_init() -> object_initialize()" initializes the object.
So we should be able to unref the MemoryRegion object directly.

We could make the PCIDevice as the owner of its IOMMU region -
when the device is finalized, its region would be finalized as well.

Given the above, I don’t think we would need a separate delete
function (such as remote_iommu_del_device()). When the device is
unplugged, its MemoryRegion would be finalized automatically.

Thank you!
--
Jag

> 
> In this case, RemoteIommuElem->mr does not have an owner. Therefore,
> we don’t have to manage its ref counter. When RemoteIommuElem is
> destroyed, the MemoryRegion should be cleaned up automatically.
> 
> --
> Jag
> 
>> 
>>> +    address_space_destroy(&elem->as);
>>> +
>>> +    g_free(elem);
>>> +}
>>> +
>>> +void remote_iommu_del_device(PCIDevice *pci_dev)
>>> +{
>>> +    int pci_bdf;
>>> +
>>> +    if (!remote_iommu_table.elem_by_bdf || !pci_dev) {
>>> +        return;
>>> +    }
>>> +
>>> +    pci_bdf = PCI_BUILD_BDF(pci_bus_num(pci_get_bus(pci_dev)), 
>>> pci_dev->devfn);
>>> +
>>> +    qemu_mutex_lock(&remote_iommu_table.lock);
>>> +    g_hash_table_remove(remote_iommu_table.elem_by_bdf, 
>>> INT2VOIDP(pci_bdf));
>>> +    qemu_mutex_unlock(&remote_iommu_table.lock);
>>> +}
>>> +
>>> +void remote_configure_iommu(PCIBus *pci_bus)
>>> +{
>>> +    if (!remote_iommu_table.elem_by_bdf) {
>>> +        remote_iommu_table.elem_by_bdf =
>>> +            g_hash_table_new_full(NULL, NULL, NULL, remote_iommu_del_elem);
>>> +        qemu_mutex_init(&remote_iommu_table.lock);
>>> +    }
>>> +
>>> +    pci_setup_iommu(pci_bus, remote_iommu_find_add_as, 
>>> &remote_iommu_table);
>>> +}
>>> diff --git a/MAINTAINERS b/MAINTAINERS
>>> index e7b0297a63..21694a9698 100644
>>> --- a/MAINTAINERS
>>> +++ b/MAINTAINERS
>>> @@ -3599,6 +3599,8 @@ F: hw/remote/iohub.c
>>> F: include/hw/remote/iohub.h
>>> F: subprojects/libvfio-user
>>> F: hw/remote/vfio-user-obj.c
>>> +F: hw/remote/iommu.c
>>> +F: include/hw/remote/iommu.h
>>> 
>>> EBPF:
>>> M: Jason Wang <jasowang@redhat.com>
>>> diff --git a/hw/remote/meson.build b/hw/remote/meson.build
>>> index 534ac5df79..bcef83c8cc 100644
>>> --- a/hw/remote/meson.build
>>> +++ b/hw/remote/meson.build
>>> @@ -6,6 +6,7 @@ remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: 
>>> files('message.c'))
>>> remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('remote-obj.c'))
>>> remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('proxy.c'))
>>> remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('iohub.c'))
>>> +remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('iommu.c'))
>>> remote_ss.add(when: 'CONFIG_VFIO_USER_SERVER', if_true: 
>>> files('vfio-user-obj.c'))
>>> 
>>> remote_ss.add(when: 'CONFIG_VFIO_USER_SERVER', if_true: vfiouser)