Re: [PATCH for-next v2 1/2] RDMA/rxe: Implement synchronous prefetch for ODP MRs

[Daisuke Matsuda <dskmtsd@gmail.com>]

On 2025/05/05 16:57, Zhu Yanjun wrote:
> On 03.05.25 15:42, Daisuke Matsuda wrote:
>> Minimal implementation of ibv_advise_mr(3) requires synchronous calls being
>> successful with the IBV_ADVISE_MR_FLAG_FLUSH flag. Asynchronous requests,
>> which are best-effort, will be added subsequently.
>>
>> Signed-off-by: Daisuke Matsuda <dskmtsd@gmail.com>
>> ---
>>   drivers/infiniband/sw/rxe/rxe.c     |  7 +++
>>   drivers/infiniband/sw/rxe/rxe_loc.h | 10 ++++
>>   drivers/infiniband/sw/rxe/rxe_odp.c | 86 +++++++++++++++++++++++++++++
>>   3 files changed, 103 insertions(+)
>>
>> diff --git a/drivers/infiniband/sw/rxe/rxe.c b/drivers/infiniband/sw/rxe/rxe.c
>> index 3a77d6db1720..e891199cbdef 100644
>> --- a/drivers/infiniband/sw/rxe/rxe.c
>> +++ b/drivers/infiniband/sw/rxe/rxe.c
>> @@ -34,6 +34,10 @@ void rxe_dealloc(struct ib_device *ib_dev)
>>       mutex_destroy(&rxe->usdev_lock);
>>   }
>> +static const struct ib_device_ops rxe_ib_dev_odp_ops = {
>> +    .advise_mr = rxe_ib_advise_mr,
>> +};
>> +
>>   /* initialize rxe device parameters */
>>   static void rxe_init_device_param(struct rxe_dev *rxe, struct net_device *ndev)
>>   {
>> @@ -103,6 +107,9 @@ static void rxe_init_device_param(struct rxe_dev *rxe, struct net_device *ndev)
>>           rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_SRQ_RECV;
>>           rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_FLUSH;
>>           rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_ATOMIC_WRITE;
>> +
>> +        /* set handler for ODP prefetching API - ibv_advise_mr(3) */
>> +        ib_set_device_ops(&rxe->ib_dev, &rxe_ib_dev_odp_ops);
>>       }
>>   }
>> diff --git a/drivers/infiniband/sw/rxe/rxe_loc.h b/drivers/infiniband/sw/rxe/rxe_loc.h
>> index f7dbb9cddd12..21b070f3dbb8 100644
>> --- a/drivers/infiniband/sw/rxe/rxe_loc.h
>> +++ b/drivers/infiniband/sw/rxe/rxe_loc.h
>> @@ -197,6 +197,9 @@ enum resp_states rxe_odp_atomic_op(struct rxe_mr *mr, u64 iova, int opcode,
>>   int rxe_odp_flush_pmem_iova(struct rxe_mr *mr, u64 iova,
>>                   unsigned int length);
>>   enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr, u64 iova, u64 value);
>> +int rxe_ib_advise_mr(struct ib_pd *pd, enum ib_uverbs_advise_mr_advice advice,
>> +             u32 flags, struct ib_sge *sg_list, u32 num_sge,
>> +             struct uverbs_attr_bundle *attrs);
>>   #else /* CONFIG_INFINIBAND_ON_DEMAND_PAGING */
>>   static inline int
>>   rxe_odp_mr_init_user(struct rxe_dev *rxe, u64 start, u64 length, u64 iova,
>> @@ -225,6 +228,13 @@ static inline enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr,
>>   {
>>       return RESPST_ERR_UNSUPPORTED_OPCODE;
>>   }
>> +static inline int rxe_ib_advise_mr(struct ib_pd *pd, enum ib_uverbs_advise_mr_advice advice,
>> +                   u32 flags, struct ib_sge *sg_list, u32 num_sge,
>> +                   struct uverbs_attr_bundle *attrs)
>> +{
>> +    return -EOPNOTSUPP;
>> +}
>> +
>>   #endif /* CONFIG_INFINIBAND_ON_DEMAND_PAGING */
>>   #endif /* RXE_LOC_H */
>> diff --git a/drivers/infiniband/sw/rxe/rxe_odp.c b/drivers/infiniband/sw/rxe/rxe_odp.c
>> index 6149d9ffe7f7..e5c60b061d7e 100644
>> --- a/drivers/infiniband/sw/rxe/rxe_odp.c
>> +++ b/drivers/infiniband/sw/rxe/rxe_odp.c
>> @@ -424,3 +424,89 @@ enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr, u64 iova, u64 value)
>>       return RESPST_NONE;
>>   }
>> +
>> +static int rxe_ib_prefetch_sg_list(struct ib_pd *ibpd,
>> +                   enum ib_uverbs_advise_mr_advice advice,
>> +                   u32 pf_flags, struct ib_sge *sg_list,
>> +                   u32 num_sge)
>> +{
>> +    struct rxe_pd *pd = container_of(ibpd, struct rxe_pd, ibpd);
>> +    unsigned int i;
>> +    int ret = 0;
>> +
>> +    for (i = 0; i < num_sge; ++i) {
> 
> i is unsigned int, num_sge is u32. Perhaps they all use u32 type?
> It is a minor problem.

Since we have dropped support for 32-bit archtectures,
these types should practically be identical.

> Other than that, I am fine with this commit.
> 
> I have made tests with rdma-core. Both the synchronous and asynchrounos modes can work well.

Thank you for the review and testing.

Daisuke

> 
> Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
> 
> Zhu Yanjun
> 
>> +        struct rxe_mr *mr;
>> +        struct ib_umem_odp *umem_odp;
>> +
>> +        mr = lookup_mr(pd, IB_ACCESS_LOCAL_WRITE,
>> +                   sg_list[i].lkey, RXE_LOOKUP_LOCAL);
>> +
>> +        if (IS_ERR(mr)) {
>> +            rxe_dbg_pd(pd, "mr with lkey %x not found\n", sg_list[i].lkey);
>> +            return PTR_ERR(mr);
>> +        }
>> +
>> +        if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_WRITE &&
>> +            !mr->umem->writable) {
>> +            rxe_dbg_mr(mr, "missing write permission\n");
>> +            rxe_put(mr);
>> +            return -EPERM;
>> +        }
>> +
>> +        ret = rxe_odp_do_pagefault_and_lock(mr, sg_list[i].addr,
>> +                            sg_list[i].length, pf_flags);
>> +        if (ret < 0) {
>> +            if (sg_list[i].length == 0)
>> +                continue;
>> +
>> +            rxe_dbg_mr(mr, "failed to prefetch the mr\n");
>> +            rxe_put(mr);
>> +            return ret;
>> +        }
>> +
>> +        umem_odp = to_ib_umem_odp(mr->umem);
>> +        mutex_unlock(&umem_odp->umem_mutex);
>> +
>> +        rxe_put(mr);
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>> +static int rxe_ib_advise_mr_prefetch(struct ib_pd *ibpd,
>> +                     enum ib_uverbs_advise_mr_advice advice,
>> +                     u32 flags, struct ib_sge *sg_list, u32 num_sge)
>> +{
>> +    u32 pf_flags = RXE_PAGEFAULT_DEFAULT;
>> +
>> +    if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH)
>> +        pf_flags |= RXE_PAGEFAULT_RDONLY;
>> +
>> +    if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_NO_FAULT)
>> +        pf_flags |= RXE_PAGEFAULT_SNAPSHOT;
>> +
>> +    /* Synchronous call */
>> +    if (flags & IB_UVERBS_ADVISE_MR_FLAG_FLUSH)
>> +        return rxe_ib_prefetch_sg_list(ibpd, advice, pf_flags, sg_list,
>> +                           num_sge);
>> +
>> +    /* Asynchronous call is "best-effort" */
>> +
>> +    return 0;
>> +}
>> +
>> +int rxe_ib_advise_mr(struct ib_pd *ibpd,
>> +             enum ib_uverbs_advise_mr_advice advice,
>> +             u32 flags,
>> +             struct ib_sge *sg_list,
>> +             u32 num_sge,
>> +             struct uverbs_attr_bundle *attrs)
>> +{
>> +    if (advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH &&
>> +        advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_WRITE &&
>> +        advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_NO_FAULT)
>> +        return -EOPNOTSUPP;
>> +
>> +    return rxe_ib_advise_mr_prefetch(ibpd, advice, flags,
>> +                     sg_list, num_sge);
>> +}
>