From: Jean-Philippe Brucker <jean-philippe@linaro.org>
To: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: iommu@lists.linux-foundation.org, devicetree@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-pci@vger.kernel.org,
linux-mm@kvack.org, joro@8bytes.org, robh+dt@kernel.org,
mark.rutland@arm.com, catalin.marinas@arm.com, will@kernel.org,
robin.murphy@arm.com, kevin.tian@intel.com,
baolu.lu@linux.intel.com, jacob.jun.pan@linux.intel.com,
christian.koenig@amd.com, yi.l.liu@intel.com,
zhangfei.gao@linaro.org,
Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Subject: Re: [PATCH v4 03/26] iommu: Add a page fault handler
Date: Fri, 28 Feb 2020 15:44:04 +0100 [thread overview]
Message-ID: <20200228144404.GD2156@myrica> (raw)
In-Reply-To: <20200226135933.000061a0@Huawei.com>
On Wed, Feb 26, 2020 at 01:59:33PM +0000, Jonathan Cameron wrote:
> > +static int iopf_complete(struct device *dev, struct iopf_fault *iopf,
> > + enum iommu_page_response_code status)
>
> This is called once per group. Should name reflect that?
Ok
[...]
> > +/**
> > + * iommu_queue_iopf - IO Page Fault handler
> > + * @evt: fault event
> > + * @cookie: struct device, passed to iommu_register_device_fault_handler.
> > + *
> > + * Add a fault to the device workqueue, to be handled by mm.
> > + *
> > + * Return: 0 on success and <0 on error.
> > + */
> > +int iommu_queue_iopf(struct iommu_fault *fault, void *cookie)
> > +{
> > + int ret;
> > + struct iopf_group *group;
> > + struct iopf_fault *iopf, *next;
> > + struct iopf_device_param *iopf_param;
> > +
> > + struct device *dev = cookie;
> > + struct iommu_param *param = dev->iommu_param;
> > +
> > + if (WARN_ON(!mutex_is_locked(¶m->lock)))
> > + return -EINVAL;
>
> Just curious...
>
> Why do we always need a runtime check on this rather than say,
> using lockdep_assert_held or similar?
I probably didn't know about lockdep_assert at the time :)
> > + /*
> > + * It is incredibly easy to find ourselves in a deadlock situation if
> > + * we're not careful, because we're taking the opposite path as
> > + * iommu_queue_iopf:
> > + *
> > + * iopf_queue_flush_dev() | PRI queue handler
> > + * lock(¶m->lock) | iommu_queue_iopf()
> > + * queue->flush() | lock(¶m->lock)
> > + * wait PRI queue empty |
> > + *
> > + * So we can't hold the device param lock while flushing. Take a
> > + * reference to the device param instead, to prevent the queue from
> > + * going away.
> > + */
> > + mutex_lock(¶m->lock);
> > + iopf_param = param->iopf_param;
> > + if (iopf_param) {
> > + queue = param->iopf_param->queue;
> > + iopf_param->busy = true;
>
> Describing this as taking a reference is not great...
> I'd change the comment to set a flag or something like that.
>
> Is there any potential of multiple copies of this running against
> each other? I've not totally gotten my head around when this
> might be called yet.
Yes it's allowed, this should be a refcount
[...]
> > +int iopf_queue_remove_device(struct iopf_queue *queue, struct device *dev)
> > +{
> > + int ret = -EINVAL;
> > + struct iopf_fault *iopf, *next;
> > + struct iopf_device_param *iopf_param;
> > + struct iommu_param *param = dev->iommu_param;
> > +
> > + if (!param || !queue)
> > + return -EINVAL;
> > +
> > + do {
> > + mutex_lock(&queue->lock);
> > + mutex_lock(¶m->lock);
> > + iopf_param = param->iopf_param;
> > + if (iopf_param && iopf_param->queue == queue) {
> > + if (iopf_param->busy) {
> > + ret = -EBUSY;
> > + } else {
> > + list_del(&iopf_param->queue_list);
> > + param->iopf_param = NULL;
> > + ret = 0;
> > + }
> > + }
> > + mutex_unlock(¶m->lock);
> > + mutex_unlock(&queue->lock);
> > +
> > + /*
> > + * If there is an ongoing flush, wait for it to complete and
> > + * then retry. iopf_param isn't going away since we're the only
> > + * thread that can free it.
> > + */
> > + if (ret == -EBUSY)
> > + wait_event(iopf_param->wq_head, !iopf_param->busy);
> > + else if (ret)
> > + return ret;
> > + } while (ret == -EBUSY);
>
> I'm in two minds about the next comment (so up to you)...
>
> Currently this looks a bit odd. Would you be better off just having a separate
> parameter for busy and explicit separate handling for the error path?
>
> bool busy;
> int ret = 0;
>
> do {
> mutex_lock(&queue->lock);
> mutex_lock(¶m->lock);
> iopf_param = param->iopf_param;
> if (iopf_param && iopf_param->queue == queue) {
> busy = iopf_param->busy;
> if (!busy) {
> list_del(&iopf_param->queue_list);
> param->iopf_param = NULL;
> }
> } else {
> ret = -EINVAL;
> }
> mutex_unlock(¶m->lock);
> mutex_unlock(&queue->lock);
> if (ret)
> return ret;
> if (busy)
> wait_event(iopf_param->wq_head, !iopf_param->busy);
>
> } while (busy);
>
> ..
Sure, I think it looks better
Thanks,
Jean
next prev parent reply other threads:[~2020-02-28 14:44 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-24 18:23 [PATCH v4 00/26] iommu: Shared Virtual Addressing and SMMUv3 support Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 01/26] mm/mmu_notifiers: pass private data down to alloc_notifier() Jean-Philippe Brucker
2020-02-24 19:00 ` Jason Gunthorpe
2020-02-25 9:24 ` Jean-Philippe Brucker
2020-02-25 14:08 ` Jason Gunthorpe
2020-02-28 14:39 ` Jean-Philippe Brucker
2020-02-28 14:48 ` Jason Gunthorpe
2020-02-28 15:04 ` Jean-Philippe Brucker
2020-02-28 15:13 ` Jason Gunthorpe
2020-03-06 9:56 ` Jean-Philippe Brucker
2020-03-06 13:09 ` Jason Gunthorpe
2020-03-06 14:35 ` Jean-Philippe Brucker
2020-03-06 14:52 ` Jason Gunthorpe
2020-03-06 16:15 ` Jean-Philippe Brucker
2020-03-06 17:42 ` Jason Gunthorpe
2020-03-13 18:49 ` Jean-Philippe Brucker
2020-03-13 19:13 ` Jason Gunthorpe
2020-03-16 15:46 ` Christoph Hellwig
2020-03-17 18:40 ` Jason Gunthorpe
2020-03-05 16:36 ` Christoph Hellwig
2020-02-24 18:23 ` [PATCH v4 02/26] iommu/sva: Manage process address spaces Jean-Philippe Brucker
2020-02-26 12:35 ` Jonathan Cameron
2020-02-28 14:43 ` Jean-Philippe Brucker
2020-02-28 16:26 ` Jonathan Cameron
2020-02-26 19:13 ` Jacob Pan
2020-02-28 14:40 ` Jean-Philippe Brucker
2020-02-28 14:57 ` Jason Gunthorpe
2020-02-24 18:23 ` [PATCH v4 03/26] iommu: Add a page fault handler Jean-Philippe Brucker
2020-02-25 3:30 ` Xu Zaibo
2020-02-25 9:25 ` Jean-Philippe Brucker
2020-02-26 3:05 ` Xu Zaibo
2020-02-26 13:59 ` Jonathan Cameron
2020-02-28 14:44 ` Jean-Philippe Brucker [this message]
2020-02-24 18:23 ` [PATCH v4 04/26] iommu/sva: Search mm by PASID Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 05/26] iommu/iopf: Handle mm faults Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 06/26] iommu/sva: Register page fault handler Jean-Philippe Brucker
2020-02-26 19:39 ` Jacob Pan
2020-02-28 14:44 ` Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 07/26] arm64: mm: Pin down ASIDs for sharing mm with devices Jean-Philippe Brucker
2020-02-27 17:43 ` Jonathan Cameron
2020-03-04 14:10 ` Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 08/26] iommu/io-pgtable-arm: Move some definitions to a header Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 09/26] iommu/arm-smmu-v3: Manage ASIDs with xarray Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 10/26] arm64: cpufeature: Export symbol read_sanitised_ftr_reg() Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 11/26] iommu/arm-smmu-v3: Share process page tables Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 12/26] iommu/arm-smmu-v3: Seize private ASID Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 13/26] iommu/arm-smmu-v3: Add support for VHE Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 14/26] iommu/arm-smmu-v3: Enable broadcast TLB maintenance Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 15/26] iommu/arm-smmu-v3: Add SVA feature checking Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 16/26] iommu/arm-smmu-v3: Add dev_to_master() helper Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 17/26] iommu/arm-smmu-v3: Implement mm operations Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 18/26] iommu/arm-smmu-v3: Hook up ATC invalidation to mm ops Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 19/26] iommu/arm-smmu-v3: Add support for Hardware Translation Table Update Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 20/26] iommu/arm-smmu-v3: Maintain a SID->device structure Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 21/26] iommu/arm-smmu-v3: Ratelimit event dump Jean-Philippe Brucker
2021-05-28 8:09 ` Aaro Koskinen
2021-05-28 16:25 ` Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 22/26] dt-bindings: document stall property for IOMMU masters Jean-Philippe Brucker
2020-02-24 18:23 ` [PATCH v4 23/26] iommu/arm-smmu-v3: Add stall support for platform devices Jean-Philippe Brucker
2020-02-26 8:44 ` Xu Zaibo
2020-03-04 14:09 ` Jean-Philippe Brucker
2020-02-27 18:17 ` Jonathan Cameron
2020-03-04 14:08 ` Jean-Philippe Brucker
2020-03-09 10:48 ` Jonathan Cameron
2020-02-24 18:23 ` [PATCH v4 24/26] PCI/ATS: Add PRI stubs Jean-Philippe Brucker
2020-02-27 20:55 ` Bjorn Helgaas
2020-02-24 18:24 ` [PATCH v4 25/26] PCI/ATS: Export symbols of PRI functions Jean-Philippe Brucker
2020-02-27 20:55 ` Bjorn Helgaas
2020-02-24 18:24 ` [PATCH v4 26/26] iommu/arm-smmu-v3: Add support for PRI Jean-Philippe Brucker
2020-02-27 18:22 ` [PATCH v4 00/26] iommu: Shared Virtual Addressing and SMMUv3 support Jonathan Cameron
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