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Date: Wed, 08 Jan 2014 14:31:05 +0800
From: Jiang Liu <jiang.liu@...ux.intel.com>
To: Kai Huang <dev.kai.huang@...il.com>
CC: Joerg Roedel <joro@...tes.org>,
David Woodhouse <dwmw2@...radead.org>,
Yinghai Lu <yinghai@...nel.org>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Dan Williams <dan.j.williams@...el.com>,
Vinod Koul <vinod.koul@...el.com>,
Tony Luck <tony.luck@...el.com>, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
iommu@...ts.linux-foundation.org
Subject: Re: [Patch Part2 V1 03/14] iommu/vt-d: simplify function get_domain_for_dev()
On 2014/1/8 14:06, Kai Huang wrote:
> On Wed, Jan 8, 2014 at 1:48 PM, Jiang Liu <jiang.liu@...ux.intel.com> wrote:
>>
>>
>> On 2014/1/8 11:06, Kai Huang wrote:
>>>
>>>
>>>
>>> On Tue, Jan 7, 2014 at 5:00 PM, Jiang Liu <jiang.liu@...ux.intel.com
>>> <mailto:jiang.liu@...ux.intel.com>> wrote:
>>>
>>> Function get_domain_for_dev() is a little complex, simplify it
>>> by factoring out dmar_search_domain_by_dev_info() and
>>> dmar_insert_dev_info().
>>>
>>> Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com
>>> <mailto:jiang.liu@...ux.intel.com>>
>>> ---
>>> drivers/iommu/intel-iommu.c | 161
>>> ++++++++++++++++++++-----------------------
>>> 1 file changed, 75 insertions(+), 86 deletions(-)
>>>
>>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>>> index 1704e97..da65884 100644
>>> --- a/drivers/iommu/intel-iommu.c
>>> +++ b/drivers/iommu/intel-iommu.c
>>> @@ -1957,18 +1957,70 @@ find_domain(struct pci_dev *pdev)
>>> return NULL;
>>> }
>>>
>>> +static inline struct dmar_domain *
>>> +dmar_search_domain_by_dev_info(int segment, int bus, int devfn)
>>> +{
>>> + struct device_domain_info *info;
>>> +
>>> + list_for_each_entry(info, &device_domain_list, global)
>>> + if (info->segment == segment && info->bus == bus &&
>>> + info->devfn == devfn)
>>> + return info->domain;
>>> +
>>> + return NULL;
>>> +}
>>> +
>>> +static int dmar_insert_dev_info(int segment, int bus, int devfn,
>>> + struct pci_dev *dev, struct
>>> dmar_domain **domp)
>>> +{
>>> + struct dmar_domain *found, *domain = *domp;
>>> + struct device_domain_info *info;
>>> + unsigned long flags;
>>> +
>>> + info = alloc_devinfo_mem();
>>> + if (!info)
>>> + return -ENOMEM;
>>> +
>>> + info->segment = segment;
>>> + info->bus = bus;
>>> + info->devfn = devfn;
>>> + info->dev = dev;
>>> + info->domain = domain;
>>> + if (!dev)
>>> + domain->flags |= DOMAIN_FLAG_P2P_MULTIPLE_DEVICES;
>>> +
>>> + spin_lock_irqsave(&device_domain_lock, flags);
>>> + if (dev)
>>> + found = find_domain(dev);
>>> + else
>>> + found = dmar_search_domain_by_dev_info(segment, bus,
>>> devfn);
>>> + if (found) {
>>> + spin_unlock_irqrestore(&device_domain_lock, flags);
>>> + free_devinfo_mem(info);
>>> + if (found != domain) {
>>> + domain_exit(domain);
>>> + *domp = found;
>>> + }
>>> + } else {
>>> + list_add(&info->link, &domain->devices);
>>> + list_add(&info->global, &device_domain_list);
>>> + if (dev)
>>> + dev->dev.archdata.iommu = info;
>>> + spin_unlock_irqrestore(&device_domain_lock, flags);
>>> + }
>>> +
>>> + return 0;
>>> +}
>>>
>>>
>>> I am a little bit confused about the "alloc before check" sequence in
>>> above function. I believe the purpose of allocating the
>>> device_domain_info before searching the domain with spin_lock hold is to
>>> avoid the memory allocation in the spin_lock? In this case, why can't we
>>> use mutex instead of spin_lock? In my understanding, if we use mutex, we
>>> can first check if the domain exists or not before we really allocate
>>> device_domain_info, right?
>> Hi Kai,
>> Thanks for review!
>> The domain->devices list may be access in interrupt context,
>> so we need to protect it with spin_lock_irqsave(). Otherwise it may
>> case deadlock.
>>
>
> Thanks. That's what I am thinking. I observed lots of other iommu
> functions also use spin_lock.
>
>>>
>>> Another question is when is info->iommu field initialized? Looks it is
>>> not initialized here?
>> It's set in function iommu_support_dev_iotlb() for devices supporting
>> device IOTLB.
>
> Thanks. I see in iommu_support_dev_iotlb, info->iommu won't be set
> unless the device supports iotlb and ATS. Does this mean the
> info->iommu won't be used if the device doesn't support iotlb?
>
> If this is true, looks it's not convenient to find the IOMMU that
> handles the device via info, as it's possible that different IOMMUs
> share the same domain, and we don't know which IOMMU actually handles
> this device if we try to find it via the info->domain.
It's a little heavy to find info by walking the list too:)
Please refer to domain_get_iommu() for the way to find iommu associated
with a domain.
>
> -Kai
>
>>
>>>
>>> -Kai
>>>
>>> +
>>> /* domain is initialized */
>>> static struct dmar_domain *get_domain_for_dev(struct pci_dev *pdev,
>>> int gaw)
>>> {
>>> - struct dmar_domain *domain, *found = NULL;
>>> + struct dmar_domain *domain;
>>> struct intel_iommu *iommu;
>>> struct dmar_drhd_unit *drhd;
>>> - struct device_domain_info *info, *tmp;
>>> - struct pci_dev *dev_tmp;
>>> + struct pci_dev *bridge;
>>> unsigned long flags;
>>> - int bus = 0, devfn = 0;
>>> - int segment;
>>> - int ret;
>>> + int segment, bus, devfn;
>>>
>>> domain = find_domain(pdev);
>>> if (domain)
>>> @@ -1976,119 +2028,56 @@ static struct dmar_domain
>>> *get_domain_for_dev(struct pci_dev *pdev, int gaw)
>>>
>>> segment = pci_domain_nr(pdev->bus);
>>>
>>> - dev_tmp = pci_find_upstream_pcie_bridge(pdev);
>>> - if (dev_tmp) {
>>> - if (pci_is_pcie(dev_tmp)) {
>>> - bus = dev_tmp->subordinate->number;
>>> + bridge = pci_find_upstream_pcie_bridge(pdev);
>>> + if (bridge) {
>>> + if (pci_is_pcie(bridge)) {
>>> + bus = bridge->subordinate->number;
>>> devfn = 0;
>>> } else {
>>> - bus = dev_tmp->bus->number;
>>> - devfn = dev_tmp->devfn;
>>> + bus = bridge->bus->number;
>>> + devfn = bridge->devfn;
>>> }
>>> spin_lock_irqsave(&device_domain_lock, flags);
>>> - list_for_each_entry(info, &device_domain_list, global) {
>>> - if (info->segment == segment &&
>>> - info->bus == bus && info->devfn == devfn) {
>>> - found = info->domain;
>>> - break;
>>> - }
>>> - }
>>> + domain = dmar_search_domain_by_dev_info(segment,
>>> bus, devfn);
>>> spin_unlock_irqrestore(&device_domain_lock, flags);
>>> /* pcie-pci bridge already has a domain, uses it */
>>> - if (found) {
>>> - domain = found;
>>> + if (domain)
>>> goto found_domain;
>>> - }
>>> }
>>>
>>> - domain = alloc_domain();
>>> - if (!domain)
>>> - goto error;
>>> -
>>> - /* Allocate new domain for the device */
>>> drhd = dmar_find_matched_drhd_unit(pdev);
>>> if (!drhd) {
>>> printk(KERN_ERR "IOMMU: can't find DMAR for device
>>> %s\n",
>>> pci_name(pdev));
>>> - free_domain_mem(domain);
>>> return NULL;
>>> }
>>> iommu = drhd->iommu;
>>>
>>> - ret = iommu_attach_domain(domain, iommu);
>>> - if (ret) {
>>> + /* Allocate new domain for the device */
>>> + domain = alloc_domain();
>>> + if (!domain)
>>> + goto error;
>>> + if (iommu_attach_domain(domain, iommu)) {
>>> free_domain_mem(domain);
>>> goto error;
>>> }
>>> -
>>> if (domain_init(domain, gaw)) {
>>> domain_exit(domain);
>>> goto error;
>>> }
>>>
>>> /* register pcie-to-pci device */
>>> - if (dev_tmp) {
>>> - info = alloc_devinfo_mem();
>>> - if (!info) {
>>> + if (bridge) {
>>> + if (dmar_insert_dev_info(segment, bus, devfn, NULL,
>>> &domain)) {
>>> domain_exit(domain);
>>> goto error;
>>> }
>>> - info->segment = segment;
>>> - info->bus = bus;
>>> - info->devfn = devfn;
>>> - info->dev = NULL;
>>> - info->domain = domain;
>>> - /* This domain is shared by devices under p2p bridge */
>>> - domain->flags |= DOMAIN_FLAG_P2P_MULTIPLE_DEVICES;
>>> -
>>> - /* pcie-to-pci bridge already has a domain, uses it */
>>> - found = NULL;
>>> - spin_lock_irqsave(&device_domain_lock, flags);
>>> - list_for_each_entry(tmp, &device_domain_list, global) {
>>> - if (tmp->segment == segment &&
>>> - tmp->bus == bus && tmp->devfn == devfn) {
>>> - found = tmp->domain;
>>> - break;
>>> - }
>>> - }
>>> - if (found) {
>>> - spin_unlock_irqrestore(&device_domain_lock,
>>> flags);
>>> - free_devinfo_mem(info);
>>> - domain_exit(domain);
>>> - domain = found;
>>> - } else {
>>> - list_add(&info->link, &domain->devices);
>>> - list_add(&info->global, &device_domain_list);
>>> - spin_unlock_irqrestore(&device_domain_lock,
>>> flags);
>>> - }
>>> }
>>>
>>> found_domain:
>>> - info = alloc_devinfo_mem();
>>> - if (!info)
>>> - goto error;
>>> - info->segment = segment;
>>> - info->bus = pdev->bus->number;
>>> - info->devfn = pdev->devfn;
>>> - info->dev = pdev;
>>> - info->domain = domain;
>>> - spin_lock_irqsave(&device_domain_lock, flags);
>>> - /* somebody is fast */
>>> - found = find_domain(pdev);
>>> - if (found != NULL) {
>>> - spin_unlock_irqrestore(&device_domain_lock, flags);
>>> - if (found != domain) {
>>> - domain_exit(domain);
>>> - domain = found;
>>> - }
>>> - free_devinfo_mem(info);
>>> + if (dmar_insert_dev_info(segment, pdev->bus->number,
>>> pdev->devfn,
>>> + pdev, &domain) == 0)
>>> return domain;
>>> - }
>>> - list_add(&info->link, &domain->devices);
>>> - list_add(&info->global, &device_domain_list);
>>> - pdev->dev.archdata.iommu = info;
>>> - spin_unlock_irqrestore(&device_domain_lock, flags);
>>> - return domain;
>>> error:
>>> /* recheck it here, maybe others set it */
>>> return find_domain(pdev);
>>> --
>>> 1.7.10.4
>>>
>>> _______________________________________________
>>> iommu mailing list
>>> iommu@...ts.linux-foundation.org
>>> <mailto:iommu@...ts.linux-foundation.org>
>>> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>>>
>>>
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