linux-kernel - Re: [PATCH v3 2/2] iommu/vt-d: avoid duplicated removing in __domain

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Date:   Fri, 8 Oct 2021 10:43:51 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Longpeng(Mike)" <longpeng2@...wei.com>, dwmw2@...radead.org,
        will@...nel.org, joro@...tes.org
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, arei.gonglei@...wei.com
Subject: Re: [PATCH v3 2/2] iommu/vt-d: avoid duplicated removing in
 __domain_mapping

On 10/8/21 10:07 AM, Lu Baolu wrote:
> On 10/8/21 8:04 AM, Longpeng(Mike) wrote:
>> __domain_mapping() always removes the pages in the range from
>> 'iov_pfn' to 'end_pfn', but the 'end_pfn' is always the last pfn
>> of the range that the caller wants to map.
>>
>> This would introduce too many duplicated removing and leads the
>> map operation take too long, for example:
>>
>>    Map iova=0x100000,nr_pages=0x7d61800
>>      iov_pfn: 0x100000, end_pfn: 0x7e617ff
>>      iov_pfn: 0x140000, end_pfn: 0x7e617ff
>>      iov_pfn: 0x180000, end_pfn: 0x7e617ff
>>      iov_pfn: 0x1c0000, end_pfn: 0x7e617ff
>>      iov_pfn: 0x200000, end_pfn: 0x7e617ff
>>      ...
>>    it takes about 50ms in total.
>>
>> We can reduce the cost by recalculate the 'end_pfn' and limit it
>> to the boundary of the end of this pte page.
>>
>>    Map iova=0x100000,nr_pages=0x7d61800
>>      iov_pfn: 0x100000, end_pfn: 0x13ffff
>>      iov_pfn: 0x140000, end_pfn: 0x17ffff
>>      iov_pfn: 0x180000, end_pfn: 0x1bffff
>>      iov_pfn: 0x1c0000, end_pfn: 0x1fffff
>>      iov_pfn: 0x200000, end_pfn: 0x23ffff
>>      ...
>>    it only need 9ms now.
>>
>> Signed-off-by: Longpeng(Mike) <longpeng2@...wei.com>
>> ---
>>   drivers/iommu/intel/iommu.c | 11 ++++++-----
>>   include/linux/intel-iommu.h |  6 ++++++
>>   2 files changed, 12 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index d75f59a..46edae6 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -2354,12 +2354,17 @@ static void switch_to_super_page(struct 
>> dmar_domain *domain,
>>                   return -ENOMEM;
>>               first_pte = pte;
>> +            lvl_pages = lvl_to_nr_pages(largepage_lvl);
>> +
>>               /* It is large page*/
>>               if (largepage_lvl > 1) {
>>                   unsigned long end_pfn;
>> +                unsigned long pages_to_remove;
>>                   pteval |= DMA_PTE_LARGE_PAGE;
>> -                end_pfn = ((iov_pfn + nr_pages) & 
>> level_mask(largepage_lvl)) - 1;
>> +                pages_to_remove = min_t(unsigned long, nr_pages,
>> +                            nr_pte_to_next_page(pte) * lvl_pages);
>> +                end_pfn = iov_pfn + pages_to_remove - 1;
>>                   switch_to_super_page(domain, iov_pfn, end_pfn, 
>> largepage_lvl);
>>               } else {
>>                   pteval &= ~(uint64_t)DMA_PTE_LARGE_PAGE;
>> @@ -2381,10 +2386,6 @@ static void switch_to_super_page(struct 
>> dmar_domain *domain,
>>               WARN_ON(1);
>>           }
>> -        lvl_pages = lvl_to_nr_pages(largepage_lvl);
>> -
>> -        BUG_ON(nr_pages < lvl_pages);
>> -
>>           nr_pages -= lvl_pages;
>>           iov_pfn += lvl_pages;
>>           phys_pfn += lvl_pages;
>> diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
>> index 9bcabc7..b29b2a3 100644
>> --- a/include/linux/intel-iommu.h
>> +++ b/include/linux/intel-iommu.h
>> @@ -713,6 +713,12 @@ static inline bool first_pte_in_page(struct 
>> dma_pte *pte)
>>       return IS_ALIGNED((unsigned long)pte, VTD_PAGE_SIZE);
>>   }
>> +static inline int nr_pte_to_next_page(struct dma_pte *pte)
>> +{
>> +    return first_pte_in_page(pte) ? BIT_ULL(VTD_STRIDE_SHIFT) :
>> +        (struct dma_pte *)ALIGN((unsigned long)pte, VTD_PAGE_SIZE) - 
>> pte;
> 
> We should make it like this to avoid the 0day warning:
> 
>      (struct dma_pte *)(uintptr_t)VTD_PAGE_ALIGN((unsigned long)pte) - pte;
> 
> Can you please test this line of change? No need to send a new version.
> I will handle it if it passes your test.

Just realized that ALIGN() has already done the type cast. Please ignore
above comment. Sorry for the noise.

Best regards,
baolu