Re: [PATCH v4 11/14] vfio-user: IOMMU support for remote device

[Jag Raman]

> On Dec 16, 2021, at 9:40 AM, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> 
> On Wed, Dec 15, 2021 at 10:35:35AM -0500, Jagannathan Raman wrote:
>> Assign separate address space for each device in the remote processes.
> 
> If I understand correctly this isn't really an IOMMU. It's abusing the
> IOMMU APIs to create isolated address spaces for each device. This way
> memory regions added by the vfio-user client do not conflict when there
> are multiple vfio-user servers.

Like you already figured out, having isolated DMA address space alone is not
sufficient for this application, we also needed to isolate the sysmem/RAM 
address
space. As such, the available IOMMU APIs alone were not sufficient, so we had
to improvise.

> 
> Calling pci_root_bus_new() and keeping one PCI bus per VfuObject might
> be a cleaner approach:
> - Lets you isolate both PCI Memory Space and IO Space.
> - Isolates the PCIDevices and their addresses on the bus.
> - Isolates irqs.
> - No more need to abuse the IOMMU API.

I believe we would still need to have an IOMMU. It’s because, devices use the
pci_dma_read()/_write() functions. These functions look up the address in DMA
address space (via pci_get_address_space() -> PCIDevice->bus_master_as ->
PCIDevice->bus_master_enable_region -> PCIDevice->bus_master_container_region).
 bus_master_enable_region and bus_master_container_region are effectively 
aliases
to the DMA address space - without an IOMMU, the dma_as would be the shared
global sysmem/RAM space (address_space_mem, please see pci_init_bus_master())

> 
> I might be missing something because I haven't investigated how to do
> this myself.
> 
>> 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/pci/pci.h      |   2 +
>> include/hw/remote/iommu.h |  24 ++++++++
>> hw/pci/pci.c              |   2 +-
>> hw/remote/iommu.c         | 117 ++++++++++++++++++++++++++++++++++++++
>> hw/remote/machine.c       |   5 ++
>> hw/remote/vfio-user-obj.c |  20 ++++++-
>> MAINTAINERS               |   2 +
>> hw/remote/meson.build     |   1 +
>> 8 files changed, 169 insertions(+), 4 deletions(-)
>> create mode 100644 include/hw/remote/iommu.h
>> create mode 100644 hw/remote/iommu.c
>> 
>> diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
>> index 5c4016b995..f2fc2d5375 100644
>> --- a/include/hw/pci/pci.h
>> +++ b/include/hw/pci/pci.h
>> @@ -734,6 +734,8 @@ void lsi53c8xx_handle_legacy_cmdline(DeviceState 
>> *lsi_dev);
>> qemu_irq pci_allocate_irq(PCIDevice *pci_dev);
>> void pci_set_irq(PCIDevice *pci_dev, int level);
>> 
>> +void pci_init_bus_master(PCIDevice *pci_dev);
> 
> This function isn't used in this patch. Why make it public?

We were investigating updating the bus’s address space before the PCI device
initialized, but we dropped it as that would be an invasive change. This is 
cruft
from that effort, sorry - will remove.

> 
>> +
>> static inline void pci_irq_assert(PCIDevice *pci_dev)
>> {
>>     pci_set_irq(pci_dev, 1);
>> diff --git a/include/hw/remote/iommu.h b/include/hw/remote/iommu.h
>> new file mode 100644
>> index 0000000000..42ce0ca383
>> --- /dev/null
>> +++ b/include/hw/remote/iommu.h
>> @@ -0,0 +1,24 @@
>> +/*
>> + * IOMMU for remote device
>> + *
>> + * Copyright © 2021 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_iommu_free(PCIDevice *pci_dev);
>> +
>> +void remote_iommu_init(void);
>> +
>> +void remote_iommu_set(PCIBus *bus);
>> +
>> +MemoryRegion *remote_iommu_get_ram(PCIDevice *pci_dev);
>> +
>> +#endif
>> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
>> index 4a84e478ce..57d561cc03 100644
>> --- a/hw/pci/pci.c
>> +++ b/hw/pci/pci.c
>> @@ -95,7 +95,7 @@ static const VMStateDescription vmstate_pcibus = {
>>     }
>> };
>> 
>> -static void pci_init_bus_master(PCIDevice *pci_dev)
>> +void pci_init_bus_master(PCIDevice *pci_dev)
>> {
>>     AddressSpace *dma_as = pci_device_iommu_address_space(pci_dev);
>> 
>> diff --git a/hw/remote/iommu.c b/hw/remote/iommu.c
>> new file mode 100644
>> index 0000000000..30c866badb
>> --- /dev/null
>> +++ b/hw/remote/iommu.c
>> @@ -0,0 +1,117 @@
>> +/*
>> + * Remote IOMMU
>> + *
>> + * Copyright © 2021 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 "exec/memory.h"
>> +#include "exec/address-spaces.h"
>> +#include "trace.h"
>> +
>> +struct VFUIOMMU {
>> +    AddressSpace  as;
>> +    MemoryRegion  mr;
> 
> I guess this is the root MemoryRegion container? Calling it "root" or
> "root_mr" instead of "mr" would make that clearer.

OK

> 
>> +};
>> +
>> +typedef struct VFUPciBus {
> 
> There is no uppercase/lowercase consistency between VfuObject vs
> VFUIOMMU vs VFUPciBus. Although the coding standard doesn't dictate ABC
> vs Abc, please be consistent. I suggest following the VfuObject
> convention started in the previous patches. The names would be VfuIommu
> and VfuPciBus.

Sounds good, thank you!

> 
>> +    PCIBus           *bus;
>> +    struct VFUIOMMU  *iommu[];
>> +} VFUPciBus;
>> +
>> +GHashTable *remote_as_table;
>> +
>> +static AddressSpace *remote_iommu_get_as(PCIBus *bus, void *opaque, int 
>> devfn)
>> +{
>> +    VFUPciBus *vfu_pci_bus = NULL;
>> +    struct VFUIOMMU *iommu = NULL;
>> +
>> +    if (!remote_as_table) {
>> +        return &address_space_memory;
>> +    }
>> +
>> +    vfu_pci_bus = g_hash_table_lookup(remote_as_table, bus);
>> +
>> +    if (!vfu_pci_bus) {
>> +        vfu_pci_bus = g_malloc0(sizeof(VFUPciBus));
>> +        vfu_pci_bus->bus = bus;
>> +        g_hash_table_insert(remote_as_table, bus, vfu_pci_bus);
>> +    }
>> +
>> +    iommu = vfu_pci_bus->iommu[devfn];
>> +
>> +    if (!iommu) {
>> +        g_autofree char *mr_name = g_strdup_printf("vfu-ram-%d", devfn);
>> +        g_autofree char *as_name = g_strdup_printf("vfu-as-%d", devfn);
>> +
>> +        iommu = g_malloc0(sizeof(struct VFUIOMMU));
>> +
>> +        memory_region_init(&iommu->mr, NULL, mr_name, UINT64_MAX);
>> +        address_space_init(&iommu->as, &iommu->mr, as_name);
>> +
>> +        vfu_pci_bus->iommu[devfn] = iommu;
>> +    }
>> +
>> +    return &iommu->as;
>> +}
>> +
>> +void remote_iommu_free(PCIDevice *pci_dev)
>> +{
>> +    VFUPciBus *vfu_pci_bus = NULL;
>> +    struct VFUIOMMU *iommu = NULL;
>> +
>> +    if (!remote_as_table) {
>> +        return;
>> +    }
>> +
>> +    vfu_pci_bus = g_hash_table_lookup(remote_as_table, 
>> pci_get_bus(pci_dev));
>> +
>> +    if (!vfu_pci_bus) {
>> +        return;
>> +    }
>> +
>> +    iommu = vfu_pci_bus->iommu[pci_dev->devfn];
>> +
>> +    vfu_pci_bus->iommu[pci_dev->devfn] = NULL;
>> +
>> +    if (iommu) {
>> +        memory_region_unref(&iommu->mr);
>> +        address_space_destroy(&iommu->as);
>> +        g_free(iommu);
>> +    }
>> +}
>> +
>> +void remote_iommu_init(void)
>> +{
>> +    remote_as_table = g_hash_table_new_full(NULL, NULL, NULL, NULL);
>> +}
>> +
>> +void remote_iommu_set(PCIBus *bus)
>> +{
>> +    pci_setup_iommu(bus, remote_iommu_get_as, NULL);
>> +}
>> +
>> +MemoryRegion *remote_iommu_get_ram(PCIDevice *pci_dev)
>> +{
>> +    PCIBus *bus = pci_get_bus(pci_dev);
>> +    VFUPciBus *vfu_pci_bus;
>> +
>> +    if (!remote_as_table) {
>> +        return get_system_memory();
>> +    }
>> +
>> +    vfu_pci_bus = g_hash_table_lookup(remote_as_table, bus);
>> +    if (!vfu_pci_bus) {
>> +        return get_system_memory();
>> +    }
>> +
>> +    return &vfu_pci_bus->iommu[pci_dev->devfn]->mr;
>> +}
>> diff --git a/hw/remote/machine.c b/hw/remote/machine.c
>> index 952105eab5..023be0491e 100644
>> --- a/hw/remote/machine.c
>> +++ b/hw/remote/machine.c
>> @@ -21,6 +21,7 @@
>> #include "qapi/error.h"
>> #include "hw/pci/pci_host.h"
>> #include "hw/remote/iohub.h"
>> +#include "hw/remote/iommu.h"
>> 
>> static void remote_machine_init(MachineState *machine)
>> {
>> @@ -52,6 +53,10 @@ static void remote_machine_init(MachineState *machine)
>> 
>>     remote_iohub_init(&s->iohub);
>> 
>> +    remote_iommu_init();
>> +
>> +    remote_iommu_set(pci_host->bus);
>> +
>>     pci_bus_irqs(pci_host->bus, remote_iohub_set_irq, remote_iohub_map_irq,
>>                  &s->iohub, REMOTE_IOHUB_NB_PIRQS);
>> }
>> diff --git a/hw/remote/vfio-user-obj.c b/hw/remote/vfio-user-obj.c
>> index 9399e87cbe..ae375e69b9 100644
>> --- a/hw/remote/vfio-user-obj.c
>> +++ b/hw/remote/vfio-user-obj.c
>> @@ -49,6 +49,7 @@
>> #include "hw/qdev-core.h"
>> #include "hw/pci/pci.h"
>> #include "qemu/timer.h"
>> +#include "hw/remote/iommu.h"
>> 
>> #define TYPE_VFU_OBJECT "x-vfio-user-server"
>> OBJECT_DECLARE_TYPE(VfuObject, VfuObjectClass, VFU_OBJECT)
>> @@ -210,6 +211,7 @@ static ssize_t vfu_object_cfg_access(vfu_ctx_t *vfu_ctx, 
>> char * const buf,
>> 
>> static void dma_register(vfu_ctx_t *vfu_ctx, vfu_dma_info_t *info)
>> {
>> +    VfuObject *o = vfu_get_private(vfu_ctx);
>>     MemoryRegion *subregion = NULL;
>>     g_autofree char *name = NULL;
>>     static unsigned int suffix;
>> @@ -226,14 +228,15 @@ static void dma_register(vfu_ctx_t *vfu_ctx, 
>> vfu_dma_info_t *info)
>>     memory_region_init_ram_ptr(subregion, NULL, name,
>>                                iov->iov_len, info->vaddr);
>> 
>> -    memory_region_add_subregion(get_system_memory(), (hwaddr)iov->iov_base,
>> -                                subregion);
>> +    memory_region_add_subregion(remote_iommu_get_ram(o->pci_dev),
>> +                                (hwaddr)iov->iov_base, subregion);
>> 
>>     trace_vfu_dma_register((uint64_t)iov->iov_base, iov->iov_len);
>> }
>> 
>> static void dma_unregister(vfu_ctx_t *vfu_ctx, vfu_dma_info_t *info)
>> {
>> +    VfuObject *o = vfu_get_private(vfu_ctx);
>>     MemoryRegion *mr = NULL;
>>     ram_addr_t offset;
>> 
>> @@ -242,7 +245,7 @@ static void dma_unregister(vfu_ctx_t *vfu_ctx, 
>> vfu_dma_info_t *info)
>>         return;
>>     }
>> 
>> -    memory_region_del_subregion(get_system_memory(), mr);
>> +    memory_region_del_subregion(remote_iommu_get_ram(o->pci_dev), mr);
>> 
>>     object_unparent((OBJECT(mr)));
>> 
>> @@ -320,6 +323,7 @@ static vfu_region_access_cb_t 
>> *vfu_object_bar_handlers[PCI_NUM_REGIONS] = {
>>  */
>> static void vfu_object_register_bars(vfu_ctx_t *vfu_ctx, PCIDevice *pdev)
>> {
>> +    VfuObject *o = vfu_get_private(vfu_ctx);
>>     int i;
>> 
>>     for (i = 0; i < PCI_NUM_REGIONS; i++) {
>> @@ -332,6 +336,12 @@ static void vfu_object_register_bars(vfu_ctx_t 
>> *vfu_ctx, PCIDevice *pdev)
>>                          vfu_object_bar_handlers[i],
>>                          VFU_REGION_FLAG_RW, NULL, 0, -1, 0);
>> 
>> +        if ((o->pci_dev->io_regions[i].type & PCI_BASE_ADDRESS_SPACE) == 0) 
>> {
>> +            memory_region_unref(o->pci_dev->io_regions[i].address_space);
>> +            o->pci_dev->io_regions[i].address_space =
>> +                remote_iommu_get_ram(o->pci_dev);
>> +        }
> 
> This looks hacky. If you create a separate PCIHost for each device
> instead then the BARs will be created in the MemoryRegion (confusingly
> named "address_space" in the PCI code) of your choosing.

I was also not very comfortable with this - added it very grudgingly out of
necessity. Thank god this can go away with separate bus for each device.

> 
> Also, why is PCI Memory Space isolated via VFUIOMMU but PCI IO Space is
> not?

If I understand correctly, the IO address space translates sysmem address to
direct device access (such as I2C). Once we are inside a device, we already
have access to all parts of the device (unlike RAM which sits outside the 
device).
So didn’t think device would go via IOMMU to access IO. Also didn’t see any
other IOMMU translating IO address space accesses.

Thank you!
--
Jag