Date:   Wed, 11 Jul 2018 15:26:21 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>, ashok.raj@...el.com,
        sanjay.k.kumar@...el.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, yi.y.sun@...el.com,
        jacob.jun.pan@...el.com
Subject: Re: [PATCH v4 6/9] iommu/vt-d: Per PCI device pasid table interfaces

Hi,

On 07/11/2018 10:18 AM, Peter Xu wrote:
> On Mon, Jul 09, 2018 at 01:22:55PM +0800, Lu Baolu wrote:
>> This patch adds the interfaces for per PCI device pasid
>> table management. Currently we allocate one pasid table
>> for all PCI devices under the scope of an IOMMU. It's
>> insecure in some cases where multiple devices under one
>> single IOMMU unit support PASID features. With per PCI
>> device pasid table, we can achieve finer protection and
>> isolation granularity.
>>
>> Cc: Ashok Raj <ashok.raj@...el.com>
>> Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
>> Cc: Kevin Tian <kevin.tian@...el.com>
>> Cc: Liu Yi L <yi.l.liu@...el.com>
>> Suggested-by: Ashok Raj <ashok.raj@...el.com>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> Reviewed-by: Liu Yi L <yi.l.liu@...el.com>
>> ---
>>  drivers/iommu/intel-iommu.c |   1 +
>>  drivers/iommu/intel-pasid.c | 178 ++++++++++++++++++++++++++++++++++++++++++++
>>  drivers/iommu/intel-pasid.h |  18 +++++
>>  drivers/iommu/intel-svm.c   |   4 -
>>  include/linux/intel-iommu.h |   2 +
>>  5 files changed, 199 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>> index 3d802c5..a930918 100644
>> --- a/drivers/iommu/intel-iommu.c
>> +++ b/drivers/iommu/intel-iommu.c
>> @@ -2450,6 +2450,7 @@ static struct dmar_domain *dmar_insert_one_dev_info(struct intel_iommu *iommu,
>>  	info->dev = dev;
>>  	info->domain = domain;
>>  	info->iommu = iommu;
>> +	info->pasid_table = NULL;
>>  
>>  	if (dev && dev_is_pci(dev)) {
>>  		struct pci_dev *pdev = to_pci_dev(info->dev);
>> diff --git a/drivers/iommu/intel-pasid.c b/drivers/iommu/intel-pasid.c
>> index e918fe0..1b61942 100644
>> --- a/drivers/iommu/intel-pasid.c
>> +++ b/drivers/iommu/intel-pasid.c
>> @@ -13,6 +13,8 @@
>>  #include <linux/intel-iommu.h>
>>  #include <linux/iommu.h>
>>  #include <linux/memory.h>
>> +#include <linux/pci.h>
>> +#include <linux/pci-ats.h>
>>  #include <linux/spinlock.h>
>>  
>>  #include "intel-pasid.h"
>> @@ -58,3 +60,179 @@ void *intel_pasid_lookup_id(int pasid)
>>  
>>  	return p;
>>  }
>> +
>> +/*
>> + * Per device pasid table management:
>> + */
>> +static inline void
>> +device_attach_pasid_table(struct device_domain_info *info,
>> +			  struct pasid_table *pasid_table)
>> +{
>> +	info->pasid_table = pasid_table;
>> +	list_add(&info->table, &pasid_table->dev);
>> +}
>> +
>> +static inline void
>> +device_detach_pasid_table(struct device_domain_info *info,
>> +			  struct pasid_table *pasid_table)
>> +{
>> +	info->pasid_table = NULL;
>> +	list_del(&info->table);
>> +}
>> +
>> +struct pasid_table_opaque {
>> +	struct pasid_table	**pasid_table;
>> +	int			segment;
>> +	int			bus;
>> +	int			devfn;
>> +};
>> +
>> +static int search_pasid_table(struct device_domain_info *info, void *opaque)
>> +{
>> +	struct pasid_table_opaque *data = opaque;
>> +
>> +	if (info->iommu->segment == data->segment &&
>> +	    info->bus == data->bus &&
>> +	    info->devfn == data->devfn &&
>> +	    info->pasid_table) {
>> +		*data->pasid_table = info->pasid_table;
>> +		return 1;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int get_alias_pasid_table(struct pci_dev *pdev, u16 alias, void *opaque)
>> +{
>> +	struct pasid_table_opaque *data = opaque;
>> +
>> +	data->segment = pci_domain_nr(pdev->bus);
>> +	data->bus = PCI_BUS_NUM(alias);
>> +	data->devfn = alias & 0xff;
>> +
>> +	return for_each_device_domain(&search_pasid_table, data);
>> +}
>> +
>> +int intel_pasid_alloc_table(struct device *dev)
>> +{
>> +	struct device_domain_info *info;
>> +	struct pasid_table *pasid_table;
>> +	struct pasid_table_opaque data;
>> +	struct page *pages;
>> +	size_t size, count;
>> +	int ret, order;
>> +
>> +	info = dev->archdata.iommu;
>> +	if (WARN_ON(!info || !dev_is_pci(dev) ||
>> +		    !info->pasid_supported || info->pasid_table))
>> +		return -EINVAL;
>> +
>> +	/* DMA alias device already has a pasid table, use it: */
>> +	data.pasid_table = &pasid_table;
>> +	ret = pci_for_each_dma_alias(to_pci_dev(dev),
>> +				     &get_alias_pasid_table, &data);
>> +	if (ret)
>> +		goto attach_out;
>> +
>> +	pasid_table = kzalloc(sizeof(*pasid_table), GFP_ATOMIC);
> Do we need to take some lock here (e.g., the pasid lock)?  Otherwise
> what if two devices (that are sharing the same DMA alias) call the
> function intel_pasid_alloc_table() concurrently, then could it
> possible that we create one table for each of the device while AFAIU
> we should let them share a single pasid table?

The only place where this function is called is in a single-thread context
(protected by a spinlock of device_domain_lock with local interrupt disabled).

So we don't need an extra lock here. But anyway, I should put a comment
here.

>
>> +	if (!pasid_table)
>> +		return -ENOMEM;
>> +	INIT_LIST_HEAD(&pasid_table->dev);
>> +
>> +	size = sizeof(struct pasid_entry);
>> +	count = min_t(int, pci_max_pasids(to_pci_dev(dev)), intel_pasid_max_id);
>> +	order = get_order(size * count);
>> +	pages = alloc_pages_node(info->iommu->node,
>> +				 GFP_ATOMIC | __GFP_ZERO,
>> +				 order);
>> +	if (!pages)
>> +		return -ENOMEM;
>> +
>> +	pasid_table->table = page_address(pages);
>> +	pasid_table->order = order;
>> +	pasid_table->max_pasid = count;
>> +
>> +attach_out:
>> +	device_attach_pasid_table(info, pasid_table);
>> +
>> +	return 0;
>> +}
>> +
>> +void intel_pasid_free_table(struct device *dev)
>> +{
>> +	struct device_domain_info *info;
>> +	struct pasid_table *pasid_table;
>> +
>> +	info = dev->archdata.iommu;
>> +	if (!info || !dev_is_pci(dev) ||
>> +	    !info->pasid_supported || !info->pasid_table)
>> +		return;
>> +
>> +	pasid_table = info->pasid_table;
>> +	device_detach_pasid_table(info, pasid_table);
>> +
>> +	if (!list_empty(&pasid_table->dev))
>> +		return;
> Same question to here: do we need a lock?

Same reason as above.

>
>> +
>> +	free_pages((unsigned long)pasid_table->table, pasid_table->order);
>> +	kfree(pasid_table);
>> +}
>> +
>> +struct pasid_table *intel_pasid_get_table(struct device *dev)
>> +{
>> +	struct device_domain_info *info;
>> +
>> +	info = dev->archdata.iommu;
>> +	if (!info)
>> +		return NULL;
>> +
>> +	return info->pasid_table;
>> +}
>> +
>> +int intel_pasid_get_dev_max_id(struct device *dev)
>> +{
>> +	struct device_domain_info *info;
>> +
>> +	info = dev->archdata.iommu;
>> +	if (!info || !info->pasid_table)
>> +		return 0;
>> +
>> +	return info->pasid_table->max_pasid;
>> +}
>> +
>> +struct pasid_entry *intel_pasid_get_entry(struct device *dev, int pasid)
>> +{
>> +	struct pasid_table *pasid_table;
>> +	struct pasid_entry *entries;
>> +
>> +	pasid_table = intel_pasid_get_table(dev);
>> +	if (WARN_ON(!pasid_table || pasid < 0 ||
>> +		    pasid >= intel_pasid_get_dev_max_id(dev)))
>> +		return NULL;
>> +
>> +	entries = pasid_table->table;
>> +
>> +	return &entries[pasid];
>> +}
>> +
>> +/*
>> + * Interfaces for PASID table entry manipulation:
>> + */
>> +static void sm_pasid_clear_entry(struct pasid_entry *pe)
>> +{
>> +	memset(pe, 0, sizeof(struct pasid_entry));
> [1]
>
>> +}
>> +
>> +void intel_pasid_clear_entry(struct device *dev, int pasid)
>> +{
>> +	struct pasid_entry *pe;
>> +
>> +	pe = intel_pasid_get_entry(dev, pasid);
>> +	if (WARN_ON(!pe))
>> +		return;
>> +
>> +	sm_pasid_clear_entry(pe);
>> +
>> +	/* Make sure the entry update is visible before translation. */
>> +	wmb();
> Pure question: AFAIU wmb only orders write operation, then do we
> really need it here?  Instead from the comment I feel like what we
> really need is a WRITE_ONCE() at [1].  Am I wrong somewhere?

I reconsidered this. Yes, you are right. I *need* a WRITE_ONCE() at [1].

Good catch! Thank you!

Best regards,
Lu Baolu

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