Re: [dpdk-dev] [PATCH v5 1/2] vhost: enable IOMMU for async vhost

["Ding, Xuan" <xuan.ding@intel.com>]

Hi,

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Tuesday, July 6, 2021 5:32 PM
> To: Burakov, Anatoly <anatoly.burakov@intel.com>; Ding, Xuan
> <xuan.ding@intel.com>; Xia, Chenbo <chenbo.xia@intel.com>; Thomas
> Monjalon <thomas@monjalon.net>; David Marchand
> <david.marchand@redhat.com>
> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; Pai G, Sunil
> <sunil.pai.g@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>; Van
> Haaren, Harry <harry.van.haaren@intel.com>; Liu, Yong <yong.liu@intel.com>;
> Ma, WenwuX <wenwux.ma@intel.com>
> Subject: Re: [dpdk-dev] [PATCH v5 1/2] vhost: enable IOMMU for async vhost
> 
> 
> 
> On 7/6/21 11:16 AM, Burakov, Anatoly wrote:
> > On 06-Jul-21 9:31 AM, Ding, Xuan wrote:
> >> Hi Maxime,
> >>
> >>> -----Original Message-----
> >>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> >>> Sent: Monday, July 5, 2021 8:46 PM
> >>> To: Burakov, Anatoly <anatoly.burakov@intel.com>; Ding, Xuan
> >>> <xuan.ding@intel.com>; Xia, Chenbo <chenbo.xia@intel.com>; Thomas
> >>> Monjalon <thomas@monjalon.net>; David Marchand
> >>> <david.marchand@redhat.com>
> >>> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; Pai G, Sunil
> >>> <sunil.pai.g@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>;
> >>> Van Haaren, Harry <harry.van.haaren@intel.com>; Liu, Yong
> >>> <yong.liu@intel.com>; Ma, WenwuX <wenwux.ma@intel.com>
> >>> Subject: Re: [dpdk-dev] [PATCH v5 1/2] vhost: enable IOMMU for async
> >>> vhost
> >>>
> >>>
> >>>
> >>> On 7/5/21 2:16 PM, Burakov, Anatoly wrote:
> >>>> On 05-Jul-21 9:40 AM, Xuan Ding wrote:
> >>>>> The use of IOMMU has many advantages, such as isolation and address
> >>>>> translation. This patch extends the capbility of DMA engine to use
> >>>>> IOMMU if the DMA device is bound to vfio.
> >>>>>
> >>>>> When set memory table, the guest memory will be mapped
> >>>>> into the default container of DPDK.
> >>>>>
> >>>>> Signed-off-by: Xuan Ding <xuan.ding@intel.com>
> >>>>> ---
> >>>>>    doc/guides/prog_guide/vhost_lib.rst |  9 ++++++
> >>>>>    lib/vhost/rte_vhost.h               |  1 +
> >>>>>    lib/vhost/socket.c                  |  9 ++++++
> >>>>>    lib/vhost/vhost.h                   |  1 +
> >>>>>    lib/vhost/vhost_user.c              | 46
> >>>>> ++++++++++++++++++++++++++++-
> >>>>>    5 files changed, 65 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/doc/guides/prog_guide/vhost_lib.rst
> >>>>> b/doc/guides/prog_guide/vhost_lib.rst
> >>>>> index 05c42c9b11..c3beda23d9 100644
> >>>>> --- a/doc/guides/prog_guide/vhost_lib.rst
> >>>>> +++ b/doc/guides/prog_guide/vhost_lib.rst
> >>>>> @@ -118,6 +118,15 @@ The following is an overview of some key Vhost
> >>>>> API functions:
> >>>>>          It is disabled by default.
> >>>>>    +  - ``RTE_VHOST_USER_ASYNC_USE_VFIO``
> >>>>> +
> >>>>> +    In asynchronous data path, vhost liarary is not aware of which
> >>>>> driver
> >>>>> +    (igb_uio/vfio) the DMA device is bound to. Application should
> >>>>> pass
> >>>>> +    this flag to tell vhost library whether IOMMU should be
> >>>>> programmed
> >>>>> +    for guest memory.
> >>>>> +
> >>>>> +    It is disabled by default.
> >>>>> +
> >>>>>      - ``RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS``
> >>>>>          Since v16.04, the vhost library forwards checksum and gso
> >>>>> requests for
> >>>>> diff --git a/lib/vhost/rte_vhost.h b/lib/vhost/rte_vhost.h
> >>>>> index 8d875e9322..a766ea7b6b 100644
> >>>>> --- a/lib/vhost/rte_vhost.h
> >>>>> +++ b/lib/vhost/rte_vhost.h
> >>>>> @@ -37,6 +37,7 @@ extern "C" {
> >>>>>    #define RTE_VHOST_USER_LINEARBUF_SUPPORT    (1ULL << 6)
> >>>>>    #define RTE_VHOST_USER_ASYNC_COPY    (1ULL << 7)
> >>>>>    #define RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS    (1ULL << 8)
> >>>>> +#define RTE_VHOST_USER_ASYNC_USE_VFIO    (1ULL << 9)
> >>>>>      /* Features. */
> >>>>>    #ifndef VIRTIO_NET_F_GUEST_ANNOUNCE
> >>>>> diff --git a/lib/vhost/socket.c b/lib/vhost/socket.c
> >>>>> index 5d0d728d52..77c722c86b 100644
> >>>>> --- a/lib/vhost/socket.c
> >>>>> +++ b/lib/vhost/socket.c
> >>>>> @@ -42,6 +42,7 @@ struct vhost_user_socket {
> >>>>>        bool extbuf;
> >>>>>        bool linearbuf;
> >>>>>        bool async_copy;
> >>>>> +    bool async_use_vfio;
> >>>>>        bool net_compliant_ol_flags;
> >>>>>          /*
> >>>>> @@ -243,6 +244,13 @@ vhost_user_add_connection(int fd, struct
> >>>>> vhost_user_socket *vsocket)
> >>>>>                dev->async_copy = 1;
> >>>>>        }
> >>>>>    +    if (vsocket->async_use_vfio) {
> >>>>> +        dev = get_device(vid);
> >>>>> +
> >>>>> +        if (dev)
> >>>>> +            dev->async_use_vfio = 1;
> >>>>> +    }
> >>>>> +
> >>>>>        VHOST_LOG_CONFIG(INFO, "new device, handle is %d\n", vid);
> >>>>>          if (vsocket->notify_ops->new_connection) {
> >>>>> @@ -879,6 +887,7 @@ rte_vhost_driver_register(const char *path,
> >>>>> uint64_t flags)
> >>>>>        vsocket->extbuf = flags & RTE_VHOST_USER_EXTBUF_SUPPORT;
> >>>>>        vsocket->linearbuf = flags &
> RTE_VHOST_USER_LINEARBUF_SUPPORT;
> >>>>>        vsocket->async_copy = flags & RTE_VHOST_USER_ASYNC_COPY;
> >>>>> +    vsocket->async_use_vfio = flags &
> >>> RTE_VHOST_USER_ASYNC_USE_VFIO;
> >>>>>        vsocket->net_compliant_ol_flags = flags &
> >>>>> RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS;
> >>>>>          if (vsocket->async_copy &&
> >>>>> diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
> >>>>> index 8078ddff79..fb775ce4ed 100644
> >>>>> --- a/lib/vhost/vhost.h
> >>>>> +++ b/lib/vhost/vhost.h
> >>>>> @@ -370,6 +370,7 @@ struct virtio_net {
> >>>>>        int16_t            broadcast_rarp;
> >>>>>        uint32_t        nr_vring;
> >>>>>        int            async_copy;
> >>>>> +    int            async_use_vfio;
> >>>>>        int            extbuf;
> >>>>>        int            linearbuf;
> >>>>>        struct vhost_virtqueue    *virtqueue[VHOST_MAX_QUEUE_PAIRS *
> >>>>> 2];
> >>>>> diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> >>>>> index 8f0eba6412..f3703f2e72 100644
> >>>>> --- a/lib/vhost/vhost_user.c
> >>>>> +++ b/lib/vhost/vhost_user.c
> >>>>> @@ -45,6 +45,7 @@
> >>>>>    #include <rte_common.h>
> >>>>>    #include <rte_malloc.h>
> >>>>>    #include <rte_log.h>
> >>>>> +#include <rte_vfio.h>
> >>>>>      #include "iotlb.h"
> >>>>>    #include "vhost.h"
> >>>>> @@ -141,6 +142,36 @@ get_blk_size(int fd)
> >>>>>        return ret == -1 ? (uint64_t)-1 : (uint64_t)stat.st_blksize;
> >>>>>    }
> >>>>>    +static int
> >>>>> +async_dma_map(struct rte_vhost_mem_region *region, bool do_map)
> >>>>> +{
> >>>>> +    int ret = 0;
> >>>>> +    uint64_t host_iova;
> >>>>> +    host_iova = rte_mem_virt2iova((void
> >>>>> *)(uintptr_t)region->host_user_addr);
> >>>>> +    if (do_map) {
> >>>>> +        /* Add mapped region into the default container of DPDK. */
> >>>>> +        ret =
> >>> rte_vfio_container_dma_map(RTE_VFIO_DEFAULT_CONTAINER_FD,
> >>>>> +                         region->host_user_addr,
> >>>>> +                         host_iova,
> >>>>> +                         region->size);
> >>>>> +        if (ret) {
> >>>>> +            VHOST_LOG_CONFIG(ERR, "DMA engine map failed\n");
> >>>>> +            return ret;
> >>>>> +        }
> >>>>> +    } else {
> >>>>> +        /* Remove mapped region from the default container of
> >>>>> DPDK. */
> >>>>> +        ret =
> >>>>> rte_vfio_container_dma_unmap(RTE_VFIO_DEFAULT_CONTAINER_FD,
> >>>>> +                           region->host_user_addr,
> >>>>> +                           host_iova,
> >>>>> +                           region->size);
> >>>>> +        if (ret) {
> >>>>> +            VHOST_LOG_CONFIG(ERR, "DMA engine unmap failed\n");
> >>>>> +            return ret;
> >>>>> +        }
> >>>>> +    }
> >>>>> +    return ret;
> >>>>> +}
> >>>>
> >>>> We've been discussing this off list with Xuan, and unfortunately
> >>>> this is
> >>>> a blocker for now.
> >>>>
> >>>> Currently, the x86 IOMMU does not support partial unmap - the segments
> >>>> have to be unmapped exactly the same addr/len as they were mapped. We
> >>>> also concatenate adjacent mappings to prevent filling up the DMA
> >>>> mapping
> >>>> entry table with superfluous entries.
> >>>>
> >>>> This means that, when two unrelated mappings are contiguous in memory
> >>>> (e.g. if you map regions 1 and 2 independently, but they happen to be
> >>>> sitting right next to each other in virtual memory), we cannot later
> >>>> unmap one of them because, even though these are two separate
> >>> mappings
> >>>> as far as kernel VFIO infrastructure is concerned, the mapping gets
> >>>> compacted and looks like one single mapping to VFIO, so DPDK API will
> >>>> not let us unmap region 1 without also unmapping region 2.
> >>>>
> >>>> The proper fix for this problem would be to always map memory
> >>>> page-by-page regardless of where it comes from (we already do that for
> >>>> internal memory, but not for external). However, the reason this works
> >>>> for internal memory is because when mapping internal memory segments,
> >>>> *we know the page size*. For external memory segments, there is no such
> >>>> guarantee, so we cannot deduce page size for a given memory segment,
> >>> and
> >>>> thus can't map things page-by-page.
> >>>>
> >>>> So, the proper fix for it would be to add page size to the VFIO DMA
> >>>> API.
> >>>> Unfortunately, it probably has to wait until 21.11 because it is an API
> >>>> change.
> >>>>
> >>>> The slightly hacky fix for this would be to forego user mem map
> >>>> concatenation and trust that user is not going to do anything stupid,
> >>>> and will not spam the VFIO DMA API without reason. I would rather
> >>>> not go
> >>>> down this road, but this could be an option in this case.
> >>>>
> >>>> Thoughts?
> >>>>
> >>>
> >>> Thanks Anatoly for the detailed description of the issue.
> >>> It may be possible to either create a versioned symbol for this API
> >>> change, or maybe even to have a temporary internal API.
> >>>
> >>> But I think this series in its current form is not acceptable, so
> >>> waiting for v21.11 would be the best option (we may want to send the
> >>> deprecation notice in this release though).
> >>>
> >>> In this series, I don't like the user application has to pass a flag to
> >>> state whether the DMA engine uses VFIO or not. AFAICT, this new revision
> >>> does not implement what was discussed in the previous one, i.e.
> >>> supporting both IOVA_AS_VA and IOVA_AS_PA.
> >>
> >> Thanks for your comments. Here I hope to explain some questions:
> >> 1. Whether both IOVA_AS_VA and IOVA_AS_PA are supported now?
> >> A: Both IOVA_AS_PA and IOVA_AS_VA are supported now. In this version, the
> >> virtual address is replaced with iova address of mapped region, and
> >> the iova
> >> address is selected to program the IOMMU instead of virtual address only.
> 
> Good!
> 
> >>
> >> 2. Why a flag is chosen to be passed by application?
> >> A: Yes, as we discussed before, the rte_eal_iova_mode() API can be
> >> used to
> >> get the IOVA mode, so as to determine whether IOMMU should be
> programmed.
> >> However, in the implementation process, I found a problem. That is how to
> >> distinguish the VFIO PA and IGB_UIO PA. Because for VFIO cases, we should
> >> always program the IOMMU. While in IGB_UIO cases, it depends on IOMMU
> >> capability of platform.
> >
> > How does one program IOMMU with igb_uio? I was under impression that
> > igb_uio (and uio_pci_generic for that matter) does not provide such
> > facilities.
> 
> +1

Maybe some misunderstanding in this sentence here.
In our design, if rte_eal_vfio_is_enabled("vfio") is true, iommu will be programmed.
True means vfio module is modprobed.
	
But there is an exception here, that is, even if vfio module is modprobed, 
DPDK user still bind all the devices to igb_uio.

This situation can be distinguished in DPDK eal initialization, because the resource mapping
is according to the driver loaded by each device(rte_pci_map_device).

But in our scenario, this judgment is somewhat weak. Because we cannot get
the device driver info in vhost library. I also think it is unreasonable for vhost to
do this. Only trust that users will not use it like this. Thoughts for this scenario?

> 
> >>
> >> So a flag is selected, but this requires the application to do extra
> >> things.
> >> I find another solution, is to use
> >> #ifdef VFIO_PRESENT
> >>          If(rte_vfio_is_enabled("vfio"))
> >>                  program_iommu;
> >> #endif
> >>
> >> Because all the devices are managed by DPDK, we can follow DPDK to do the
> >> decision. Does this make sense for you, or any some suggestions?
> >
> > IMO the #ifdef is not needed. The API will always work, it's just that
> > if VFIO is not compiled, it'll just compile down to noops.
> 
> Agree the #ifdef is not necessary.

Thanks, I will remove the #ifdef in next version.
Only use rte_vfio_is_enabled("vfio").

> 
> To be clear, rte_vfio_is_enabled() check is going to be done in the
> Vhost library, making this transparent to the application?

Yes, you are right :)
The check will be done in vhost library, application does not need to do
additional things.

> 
> >>
> >> 3.  The partial unmap issue
> >> A: Thanks Anatoly for the detailed explanation. This problem was found in
> >> reconnection cases. After our off list discussion, the solution requires
> >> rte_vfio_container_dma_map/unmap API change. Here I want to consult
> >> if there are some hope for versioned symbol or a temporary internal API
> >> be used in this release.
> >
> > I don't think we can add a versioned symbol in this release unless
> > there's an exception to rc1 feature freeze. I also don't like the idea
> > of a temporary internal API because vhost is not in EAL, it's a library
> > - meaning, the "internal" API has to in fact be external API, added to
> > the .map file etc., otherwise it won't work with shared library builds.

Get it, thanks for your suggestion.

> >
> > That said, i'm not an expert on versioning, so maybe there are other
> > ways i'm not aware of, or i have some misconceptions about how it works :)
> 
> Ok, it maybe indeed be better to wait for v21.11, it is too late for
> this release.

Agree, so I will send a new version in v21.11.

Thanks,
Xuan

> 
> Thanks,
> Maxime
> 
> >>
> >> Thanks for your time!
> >>
> >> Regards,
> >> Xuan
> >>
> >>>
> >>> Regards,
> >>> Maxime
> >>
> >
> >