netdev - Re: [PATCH net-next v5 08/13] net: wwan: t7xx: Add data path interface

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHNKnsRrvz+pnpeGoJdRDD=Qto3eQR79E29Jz2k2kKM0vXMaTQ@mail.gmail.com>
Date:   Tue, 5 Apr 2022 02:50:49 +0300
From:   Sergey Ryazanov <ryazanov.s.a@...il.com>
To:     "Martinez, Ricardo" <ricardo.martinez@...ux.intel.com>
Cc:     netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Johannes Berg <johannes@...solutions.net>,
        Loic Poulain <loic.poulain@...aro.org>,
        M Chetan Kumar <m.chetan.kumar@...el.com>,
        chandrashekar.devegowda@...el.com,
        Intel Corporation <linuxwwan@...el.com>,
        chiranjeevi.rapolu@...ux.intel.com,
        Haijun Liu (刘海军) 
        <haijun.liu@...iatek.com>, amir.hanania@...el.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        dinesh.sharma@...el.com, eliot.lee@...el.com,
        ilpo.johannes.jarvinen@...el.com, moises.veleta@...el.com,
        pierre-louis.bossart@...el.com, muralidharan.sethuraman@...el.com,
        Soumya.Prakash.Mishra@...el.com, sreehari.kancharla@...el.com,
        madhusmita.sahu@...el.com
Subject: Re: [PATCH net-next v5 08/13] net: wwan: t7xx: Add data path interface

Hello Ricardo,

On Tue, Apr 5, 2022 at 2:29 AM Martinez, Ricardo
<ricardo.martinez@...ux.intel.com> wrote:
> On 3/6/2022 6:58 PM, Sergey Ryazanov wrote:
>> On Thu, Feb 24, 2022 at 1:35 AM Ricardo Martinez
>> <ricardo.martinez@...ux.intel.com> wrote:
>>> From: Haijun Liu <haijun.liu@...iatek.com>
>>>
>>> Data Path Modem AP Interface (DPMAIF) HIF layer provides methods
>>> for initialization, ISR, control and event handling of TX/RX flows.
>>>
>>> DPMAIF TX
>>> Exposes the `dmpaif_tx_send_skb` function which can be used by the
>>> network device to transmit packets.
>>> The uplink data management uses a Descriptor Ring Buffer (DRB).
>>> First DRB entry is a message type that will be followed by 1 or more
>>> normal DRB entries. Message type DRB will hold the skb information
>>> and each normal DRB entry holds a pointer to the skb payload.
>>>
>>> DPMAIF RX
>>> The downlink buffer management uses Buffer Address Table (BAT) and
>>> Packet Information Table (PIT) rings.
>>> The BAT ring holds the address of skb data buffer for the HW to use,
>>> while the PIT contains metadata about a whole network packet including
>>> a reference to the BAT entry holding the data buffer address.
>>> The driver reads the PIT and BAT entries written by the modem, when
>>> reaching a threshold, the driver will reload the PIT and BAT rings.
> ...
>>> +static int t7xx_dpmaif_add_skb_to_ring(struct dpmaif_ctrl *dpmaif_ctrl, struct sk_buff *skb)
>>> +{
>>> +       unsigned short cur_idx, drb_wr_idx_backup;
>>> ...
>>> +       txq = &dpmaif_ctrl->txq[skb_cb->txq_number];
>>> ...
>>> +       cur_idx = txq->drb_wr_idx;
>>> +       drb_wr_idx_backup = cur_idx;
>>> ...
>>> +       for (wr_cnt = 0; wr_cnt < payload_cnt; wr_cnt++) {
>>> ...
>>> +               bus_addr = dma_map_single(dpmaif_ctrl->dev, data_addr, data_len, DMA_TO_DEVICE);
>>> +               if (dma_mapping_error(dpmaif_ctrl->dev, bus_addr)) {
>>> +                       dev_err(dpmaif_ctrl->dev, "DMA mapping fail\n");
>>> +                       atomic_set(&txq->tx_processing, 0);
>>> +
>>> +                       spin_lock_irqsave(&txq->tx_lock, flags);
>>> +                       txq->drb_wr_idx = drb_wr_idx_backup;
>>> +                       spin_unlock_irqrestore(&txq->tx_lock, flags);
>>
>> What is the purpose of locking here?
>
> The intention is to protect against concurrent access of drb_wr_idx by t7xx_txq_drb_wr_available()

t7xx_txq_drb_wr_available() only reads the drb_wr_idx field, why would
you serialize that concurrent read?

>>> +                       return -ENOMEM;
>>> +               }
>>> ...
>>> +       }
>>> ...
>>> +}

-- 
Sergey