linux-kernel - Re: [PATCH v4 5/9] iommu/vt-d: Don't switch off swiotlb if use direct dma

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Date:   Wed, 12 Jun 2019 10:03:52 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     baolu.lu@...ux.intel.com, David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Christoph Hellwig <hch@....de>, ashok.raj@...el.com,
        jacob.jun.pan@...el.com, alan.cox@...el.com, kevin.tian@...el.com,
        mika.westerberg@...ux.intel.com, Ingo Molnar <mingo@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        pengfei.xu@...el.com, Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Jonathan Corbet <corbet@....net>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...el.com>
Subject: Re: [PATCH v4 5/9] iommu/vt-d: Don't switch off swiotlb if use direct
 dma

Hi,

On 6/10/19 11:54 PM, Konrad Rzeszutek Wilk wrote:
> On Mon, Jun 03, 2019 at 09:16:16AM +0800, Lu Baolu wrote:
>> The direct dma implementation depends on swiotlb. Hence, don't
>> switch of swiotlb since direct dma interfaces are used in this
> 
> s/of/off/

Yes.

> 
>> driver.
> 
> But I think you really want to leave the code as is but change
> the #ifdef to check for IOMMU_BOUNCE_PAGE and not CONFIG_SWIOTLB.
> 
> As one could disable IOMMU_BOUNCE_PAGE.

SWIOTLB is not only used when IOMMU_BOUCE_PAGE is enabled.

Please check this code:

static dma_addr_t intel_map_page(struct device *dev, struct page *page,
                                  unsigned long offset, size_t size,
                                  enum dma_data_direction dir,
                                  unsigned long attrs)
{
         if (iommu_need_mapping(dev))
                 return __intel_map_single(dev, page_to_phys(page) + offset,
                                 size, dir, *dev->dma_mask);
         return dma_direct_map_page(dev, page, offset, size, dir, attrs);
}

The dma_direct_map_page() will eventually call swiotlb_map() if the
buffer is beyond the address capability of the device.

Best regards,
Baolu

>>
>> Cc: Ashok Raj <ashok.raj@...el.com>
>> Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
>> Cc: Kevin Tian <kevin.tian@...el.com>
>> Cc: Mika Westerberg <mika.westerberg@...el.com>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/intel-iommu.c | 6 ------
>>   1 file changed, 6 deletions(-)
>>
>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>> index d5a6c8064c56..235837c50719 100644
>> --- a/drivers/iommu/intel-iommu.c
>> +++ b/drivers/iommu/intel-iommu.c
>> @@ -4625,9 +4625,6 @@ static int __init platform_optin_force_iommu(void)
>>   		iommu_identity_mapping |= IDENTMAP_ALL;
>>   
>>   	dmar_disabled = 0;
>> -#if defined(CONFIG_X86) && defined(CONFIG_SWIOTLB)
>> -	swiotlb = 0;
>> -#endif
>>   	no_iommu = 0;
>>   
>>   	return 1;
>> @@ -4765,9 +4762,6 @@ int __init intel_iommu_init(void)
>>   	}
>>   	up_write(&dmar_global_lock);
>>   
>> -#if defined(CONFIG_X86) && defined(CONFIG_SWIOTLB)
>> -	swiotlb = 0;
>> -#endif
>>   	dma_ops = &intel_dma_ops;
>>   
>>   	init_iommu_pm_ops();
>> -- 
>> 2.17.1
>>
>