linux-kernel - Re: [RFC v2 8/8] iommu/arm-smmu: implement add_reserved

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Date:   Thu, 10 Nov 2016 16:57:51 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     eric.auger.pro@...il.com, christoffer.dall@...aro.org,
        marc.zyngier@....com, robin.murphy@....com,
        alex.williamson@...hat.com, will.deacon@....com,
        tglx@...utronix.de, jason@...edaemon.net,
        linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
        drjones@...hat.com, linux-kernel@...r.kernel.org,
        pranav.sawargaonkar@...il.com, iommu@...ts.linux-foundation.org,
        punit.agrawal@....com, diana.craciun@....com
Subject: Re: [RFC v2 8/8] iommu/arm-smmu: implement add_reserved_regions
 callback

Hi Joerg,

On 10/11/2016 16:46, Joerg Roedel wrote:
> On Fri, Nov 04, 2016 at 11:24:06AM +0000, Eric Auger wrote:
>> The function populates the list of reserved regions with the
>> PCI host bridge windows and the MSI IOVA range.
>>
>> At the moment an arbitray MSI IOVA window is set at 0x8000000
>> of size 1MB.
>>
>> Signed-off-by: Eric Auger <eric.auger@...hat.com>
>>
>> ---
>>
>> RFC v1 -> v2: use defines for MSI IOVA base and length
>> ---
>>  drivers/iommu/arm-smmu.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 66 insertions(+)
>>
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index c841eb7..c07ea41 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -278,6 +278,9 @@ enum arm_smmu_s2cr_privcfg {
>>  
>>  #define FSYNR0_WNR			(1 << 4)
>>  
>> +#define MSI_IOVA_BASE			0x8000000
>> +#define MSI_IOVA_LENGTH			0x100000
>> +
>>  static int force_stage;
>>  module_param(force_stage, int, S_IRUGO);
>>  MODULE_PARM_DESC(force_stage,
>> @@ -1533,6 +1536,68 @@ static int arm_smmu_of_xlate(struct device *dev, struct of_phandle_args *args)
>>  	return iommu_fwspec_add_ids(dev, &fwid, 1);
>>  }
>>  
>> +static int add_pci_window_reserved_regions(struct iommu_domain *domain,
>> +					   struct pci_dev *dev)
>> +{
>> +	struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
>> +	struct iommu_reserved_region *region;
>> +	struct resource_entry *window;
>> +	phys_addr_t start;
>> +	size_t length;
>> +
>> +	resource_list_for_each_entry(window, &bridge->windows) {
>> +		if (resource_type(window->res) != IORESOURCE_MEM &&
>> +		    resource_type(window->res) != IORESOURCE_IO)
>> +			continue;
> 
> Why do you care about IO resources?
Effectively that's a draft implementation inspired from "iommu/dma:
Avoid PCI host bridge windows". Also not all PCI host bridge windows
induce issues; my understanding is only those not supporting ACS are a
problem.
> 
>> +
>> +		start = window->res->start - window->offset;
>> +		length = window->res->end - window->res->start + 1;
>> +
>> +		iommu_reserved_region_for_each(region, domain) {
>> +			if (region->start == start && region->length == length)
>> +				continue;
>> +		}
>> +		region = kzalloc(sizeof(*region), GFP_KERNEL);
>> +		if (!region)
>> +			return -ENOMEM;
>> +
>> +		region->start = start;
>> +		region->length = length;
>> +
>> +		list_add_tail(&region->list, &domain->reserved_regions);
>> +	}
>> +	return 0;
>> +}
>> +
>> +static int arm_smmu_add_reserved_regions(struct iommu_domain *domain,
>> +					 struct device *device)
>> +{
>> +	struct iommu_reserved_region *region;
>> +	int ret = 0;
>> +
>> +	/* An arbitrary 1MB region starting at 0x8000000 is reserved for MSIs */
>> +	if (!domain->iova_cookie) {
>> +
>> +		region = kzalloc(sizeof(*region), GFP_KERNEL);
>> +		if (!region)
>> +			return -ENOMEM;
>> +
>> +		region->start = MSI_IOVA_BASE;
>> +		region->length = MSI_IOVA_LENGTH;
>> +		list_add_tail(&region->list, &domain->reserved_regions);
>> +
>> +		ret = iommu_get_dma_msi_region_cookie(domain,
>> +						region->start, region->length);
>> +		if (ret)
>> +			return ret;
> 
> Gah, I hate this. Is there no other and simpler way to get the MSI
> region than allocating an iova-domain? In that regard, I also _hate_ the
> patch before introducing this weird iommu_get_dma_msi_region_cookie()
> function.
> 
> Allocation an iova-domain is pretty expensive, as it also includes
> per-cpu data-structures and all, so please don't do this just for the
> purpose of compiling a list of reserved regions.
It does not only serve the purpose to register the MSI IOVA region. We
also need to allocate an iova_domain where MSI IOVAs will be allocated
upon the request of the relevant MSI controllers. Do you mean you don't
like to use the iova allocator for this purpose?

Thanks

Eric
> 
> 
> 
> 	Joerg
>