From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D5889C19F28 for ; Wed, 3 Aug 2022 11:40:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237607AbiHCLkK (ORCPT ); Wed, 3 Aug 2022 07:40:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58406 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236088AbiHCLkG (ORCPT ); Wed, 3 Aug 2022 07:40:06 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 541A31054C for ; Wed, 3 Aug 2022 04:40:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659526804; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=JwfvYO99TCB9FiKX3BYcocI/S5+Oq3USCEZauc8Ysww=; b=Y9K08+BU22N8Am63BEFKxuUhvTwgsssPilFl65hI9xdNNnCTkUWWZsOCYleTN3+OZfb7Ng PAB5ZitGAPBnwWZ0TkRYjYjonqTUAuQdixTweULcokrZTJCcuN8M2fpXEP0ifPeRjBXNi2 IAeeqGTVjUk8vMHP7z4ExdAAwu7wvNc= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-125-_abjqHj5NZWB3OuLR3Qyag-1; Wed, 03 Aug 2022 07:40:03 -0400 X-MC-Unique: _abjqHj5NZWB3OuLR3Qyag-1 Received: by mail-wr1-f71.google.com with SMTP id w22-20020adf8bd6000000b002206311fb96so2261245wra.12 for ; Wed, 03 Aug 2022 04:40:03 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc; bh=JwfvYO99TCB9FiKX3BYcocI/S5+Oq3USCEZauc8Ysww=; b=mLr/xSRobVn5rhVXvvPuocVlu/YRU4XIPJ2xSX5kJ9WkxS6TtbdPhWgOLO29AJr8q8 P6ur/YCTsgMG7Dmh5ttc4JuFp968W1/BgJWl5S2o+KPkCpijBAP2phwXU9fMyv+76k1u AUKEbo0ac38063Rxmp5Ne7ClpQ6Oz/c1VSE0BqaF1Ou5lA9/jX/U0UWWZNuMyITHaBNr EL00KdV62jCqNzaXJwcnOox4FcGD7f2Eg4+hbjZyfBpCaY8rZ5ITlDqkPlifD2GjDDSQ py1ogKBrmXdaxDSUMzSjUHkqYRngrN/4Apbjbcifc/3fAWcdwGzV37HYjRHnPeGRO8tW 3eMQ== X-Gm-Message-State: ACgBeo3xOofONrcCT4N98ps5Ps4s1pOVWcZPJVPSHGf+VgOpTPBbZk++ eW4CCxvAu91AdXYIgan+2D+a5d/Ij3m0nGfJaBPCBHnt8BojvoIaa4gb6HOAiJDwP4DLYSJcKo2 PWpnkGZPJnTFye1MFxy/mzzXY X-Received: by 2002:a05:600c:5029:b0:3a3:7308:6a43 with SMTP id n41-20020a05600c502900b003a373086a43mr2482222wmr.99.1659526801885; Wed, 03 Aug 2022 04:40:01 -0700 (PDT) X-Google-Smtp-Source: AA6agR7Rj/RNdfFfFtzgtWn3I7gaknofBvNO8dT4fRFSg4D4OhE4MQPKh3aT/w+L1QYSSL2Mvr0VaA== X-Received: by 2002:a05:600c:5029:b0:3a3:7308:6a43 with SMTP id n41-20020a05600c502900b003a373086a43mr2482207wmr.99.1659526801602; Wed, 03 Aug 2022 04:40:01 -0700 (PDT) Received: from redhat.com ([2.54.191.86]) by smtp.gmail.com with ESMTPSA id a1-20020adfe5c1000000b0021e491fd250sm11957635wrn.89.2022.08.03.04.39.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Aug 2022 04:40:01 -0700 (PDT) Date: Wed, 3 Aug 2022 07:39:57 -0400 From: "Michael S. Tsirkin" To: Vladimir Murzin Cc: Laurent Vivier , linux-kernel@vger.kernel.org, amit@kernel.org, Herbert Xu , Matt Mackall , virtualization@lists.linux-foundation.org, Dmitriy Vyukov , rusty@rustcorp.com.au, akong@redhat.com, Alexander Potapenko , linux-crypto@vger.kernel.org, Mauricio De Carvalho , Kevin Brodsky Subject: Re: [PATCH v2 4/4] hwrng: virtio - always add a pending request Message-ID: <20220803073243-mutt-send-email-mst@kernel.org> References: <20211028101111.128049-1-lvivier@redhat.com> <20211028101111.128049-5-lvivier@redhat.com> <7e64ce61-89b1-40aa-8295-00ca42b9a959@arm.com> <2c1198c4-77aa-5cb8-6bb4-b974850651be@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2c1198c4-77aa-5cb8-6bb4-b974850651be@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 03, 2022 at 09:57:35AM +0100, Vladimir Murzin wrote: > On 8/2/22 13:49, Vladimir Murzin wrote: > > Hi Laurent, > > > > On 10/28/21 11:11, Laurent Vivier wrote: > >> If we ensure we have already some data available by enqueuing > >> again the buffer once data are exhausted, we can return what we > >> have without waiting for the device answer. > >> > >> Signed-off-by: Laurent Vivier > >> --- > >> drivers/char/hw_random/virtio-rng.c | 26 ++++++++++++-------------- > >> 1 file changed, 12 insertions(+), 14 deletions(-) > >> > >> diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c > >> index 8ba97cf4ca8f..0a7dde135db1 100644 > >> --- a/drivers/char/hw_random/virtio-rng.c > >> +++ b/drivers/char/hw_random/virtio-rng.c > >> @@ -20,7 +20,6 @@ struct virtrng_info { > >> struct virtqueue *vq; > >> char name[25]; > >> int index; > >> - bool busy; > >> bool hwrng_register_done; > >> bool hwrng_removed; > >> /* data transfer */ > >> @@ -44,16 +43,18 @@ static void random_recv_done(struct virtqueue *vq) > >> return; > >> > >> vi->data_idx = 0; > >> - vi->busy = false; > >> > >> complete(&vi->have_data); > >> } > >> > >> -/* The host will fill any buffer we give it with sweet, sweet randomness. */ > >> -static void register_buffer(struct virtrng_info *vi) > >> +static void request_entropy(struct virtrng_info *vi) > >> { > >> struct scatterlist sg; > >> > >> + reinit_completion(&vi->have_data); > >> + vi->data_avail = 0; > >> + vi->data_idx = 0; > >> + > >> sg_init_one(&sg, vi->data, sizeof(vi->data)); > >> > >> /* There should always be room for one buffer. */ > >> @@ -69,6 +70,8 @@ static unsigned int copy_data(struct virtrng_info *vi, void *buf, > >> memcpy(buf, vi->data + vi->data_idx, size); > >> vi->data_idx += size; > >> vi->data_avail -= size; > >> + if (vi->data_avail == 0) > >> + request_entropy(vi); > >> return size; > >> } > >> > >> @@ -98,13 +101,7 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait) > >> * so either size is 0 or data_avail is 0 > >> */ > >> while (size != 0) { > >> - /* data_avail is 0 */ > >> - if (!vi->busy) { > >> - /* no pending request, ask for more */ > >> - vi->busy = true; > >> - reinit_completion(&vi->have_data); > >> - register_buffer(vi); > >> - } > >> + /* data_avail is 0 but a request is pending */ > >> ret = wait_for_completion_killable(&vi->have_data); > >> if (ret < 0) > >> return ret; > >> @@ -126,8 +123,7 @@ static void virtio_cleanup(struct hwrng *rng) > >> { > >> struct virtrng_info *vi = (struct virtrng_info *)rng->priv; > >> > >> - if (vi->busy) > >> - complete(&vi->have_data); > >> + complete(&vi->have_data); > >> } > >> > >> static int probe_common(struct virtio_device *vdev) > >> @@ -163,6 +159,9 @@ static int probe_common(struct virtio_device *vdev) > >> goto err_find; > >> } > >> > >> + /* we always have a pending entropy request */ > >> + request_entropy(vi); > >> + > >> return 0; > >> > >> err_find: > >> @@ -181,7 +180,6 @@ static void remove_common(struct virtio_device *vdev) > >> vi->data_idx = 0; > >> complete(&vi->have_data); > >> vdev->config->reset(vdev); > >> - vi->busy = false; > >> if (vi->hwrng_register_done) > >> hwrng_unregister(&vi->hwrng); > >> vdev->config->del_vqs(vdev); > > > > We observed that after this commit virtio-rng implementation in FVP doesn't > > work > > > > INFO: bp.virtio_rng: Selected Random Generator Device: XORSHIFT DEVICE > > INFO: bp.virtio_rng: Using seed value: 0x5674bba8 > > Error: FVP_Base_AEMvA: bp.virtio_rng: Found invalid descriptor index > > In file: (unknown):0 > > In process: FVP_Base_AEMvA.thread_p_12 @ 935500020 ns > > Info: FVP_Base_AEMvA: bp.virtio_rng: Could not extract buffer > > > > while basic baremetal test works as expected > > > > INFO: bp.virtio_rng: Selected Random Generator Device: XORSHIFT DEVICE > > INFO: bp.virtio_rng: Using seed value: 0x541c142e > > Info: FVP_Base_AEMv8A: bp.virtio_rng: Generated Number: 0x4b098991ceb377e6 > > Info: FVP_Base_AEMv8A: bp.virtio_rng: Generated Number: 0xbdcbe3f765ba62f7 > > > > We are trying to get an idea what is missing and where, yet none of us familiar > > with the driver :( > > > > I'm looping Kevin who originally reported that and Mauricio who is looking form > > the FVP side. > > With the following diff FVP works agin > > diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c > index a6f3a8a2ac..042503ad6c 100644 > --- a/drivers/char/hw_random/virtio-rng.c > +++ b/drivers/char/hw_random/virtio-rng.c > @@ -54,6 +54,7 @@ static void request_entropy(struct virtrng_info *vi) > reinit_completion(&vi->have_data); > vi->data_avail = 0; > vi->data_idx = 0; > + smp_mb(); > > sg_init_one(&sg, vi->data, sizeof(vi->data)); > > > What do you reckon? > > Cheers > Vladimir Thanks for debugging this! OK, interesting. data_idx and data_avail are accessed from virtio_read. Which as far as I can tell is invoked just with reading_mutex. But, request_entropy is called from probe when device is registered this time without locks so it can trigger while another thread is calling virtio_read. Second request_entropy is called from a callback random_recv_done also without locks. So it's great that smp_mb helped here but I suspect in fact we need locking. Laurent? -- MST