RE: [PATCH v3 2/2] iommu/vt-d: avoid duplicated removing in __domain_mapping

["Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" <longpeng2@huawei.com>]

> -----Original Message-----
> From: Lu Baolu [mailto:baolu.lu@linux.intel.com]
> Sent: Friday, October 8, 2021 10:44 AM
> To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> <longpeng2@huawei.com>; dwmw2@infradead.org; will@kernel.org;
> joro@8bytes.org
> Cc: baolu.lu@linux.intel.com; iommu@lists.linux-foundation.org;
> linux-kernel@vger.kernel.org; Gonglei (Arei) <arei.gonglei@huawei.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@huawei.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.
> 

Hi Baolu,

Our testing is completed, no compile warning on both X86 64bit and 32bit arch,
and the system is working as expected.

Please add:

Tested-by: Liujunjie <liujunjie23@huawei.com>

> Best regards,
> baolu