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Date:   Fri, 9 Apr 2021 13:31:13 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     baolu.lu@...ux.intel.com, David Woodhouse <dwmw2@...radead.org>,
        Nadav Amit <nadav.amit@...il.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        "Gonglei (Arei)" <arei.gonglei@...wei.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] iommu/vt-d: Force to flush iotlb before creating
 superpage

Hi Longpeng,

On 4/8/21 3:37 PM, Longpeng (Mike, Cloud Infrastructure Service Product 
Dept.) wrote:
> Hi Baolu,
> 
>> -----Original Message-----
>> From: Lu Baolu [mailto:baolu.lu@...ux.intel.com]
>> Sent: Thursday, April 8, 2021 12:32 PM
>> To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
>> <longpeng2@...wei.com>; iommu@...ts.linux-foundation.org;
>> linux-kernel@...r.kernel.org
>> Cc: baolu.lu@...ux.intel.com; David Woodhouse <dwmw2@...radead.org>; Nadav
>> Amit <nadav.amit@...il.com>; Alex Williamson <alex.williamson@...hat.com>;
>> Kevin Tian <kevin.tian@...el.com>; Gonglei (Arei) <arei.gonglei@...wei.com>;
>> stable@...r.kernel.org
>> Subject: Re: [PATCH] iommu/vt-d: Force to flush iotlb before creating superpage
>>
>> Hi Longpeng,
>>
>> On 4/7/21 2:35 PM, Longpeng (Mike, Cloud Infrastructure Service Product
>> Dept.) wrote:
>>> Hi Baolu,
>>>
>>>> -----Original Message-----
>>>> From: Lu Baolu [mailto:baolu.lu@...ux.intel.com]
>>>> Sent: Friday, April 2, 2021 12:44 PM
>>>> To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
>>>> <longpeng2@...wei.com>; iommu@...ts.linux-foundation.org;
>>>> linux-kernel@...r.kernel.org
>>>> Cc: baolu.lu@...ux.intel.com; David Woodhouse <dwmw2@...radead.org>;
>>>> Nadav Amit <nadav.amit@...il.com>; Alex Williamson
>>>> <alex.williamson@...hat.com>; Kevin Tian <kevin.tian@...el.com>;
>>>> Gonglei (Arei) <arei.gonglei@...wei.com>; stable@...r.kernel.org
>>>> Subject: Re: [PATCH] iommu/vt-d: Force to flush iotlb before creating
>>>> superpage
>>>>
>>>> Hi Longpeng,
>>>>
>>>> On 4/1/21 3:18 PM, Longpeng(Mike) wrote:
>>>>> diff --git a/drivers/iommu/intel/iommu.c
>>>>> b/drivers/iommu/intel/iommu.c index ee09323..cbcb434 100644
>>>>> --- a/drivers/iommu/intel/iommu.c
>>>>> +++ b/drivers/iommu/intel/iommu.c
>>>>> @@ -2342,9 +2342,20 @@ static inline int
>>>>> hardware_largepage_caps(struct
>>>> dmar_domain *domain,
>>>>>     				 * removed to make room for superpage(s).
>>>>>     				 * We're adding new large pages, so make sure
>>>>>     				 * we don't remove their parent tables.
>>>>> +				 *
>>>>> +				 * We also need to flush the iotlb before creating
>>>>> +				 * superpage to ensure it does not perserves any
>>>>> +				 * obsolete info.
>>>>>     				 */
>>>>> -				dma_pte_free_pagetable(domain, iov_pfn, end_pfn,
>>>>> -						       largepage_lvl + 1);
>>>>> +				if (dma_pte_present(pte)) {
>>>>
>>>> The dma_pte_free_pagetable() clears a batch of PTEs. So checking
>>>> current PTE is insufficient. How about removing this check and always
>>>> performing cache invalidation?
>>>>
>>>
>>> Um...the PTE here may be present( e.g. 4K mapping --> superpage mapping )
>> orNOT-present ( e.g. create a totally new superpage mapping ), but we only need to
>> call free_pagetable and flush_iotlb in the former case, right ?
>>
>> But this code covers multiple PTEs and perhaps crosses the page boundary.
>>
>> How about moving this code into a separated function and check PTE presence
>> there. A sample code could look like below: [compiled but not tested!]
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index
>> d334f5b4e382..0e04d450c38a 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -2300,6 +2300,41 @@ static inline int hardware_largepage_caps(struct
>> dmar_domain *domain,
>>           return level;
>>    }
>>
>> +/*
>> + * Ensure that old small page tables are removed to make room for
>> superpage(s).
>> + * We're going to add new large pages, so make sure we don't remove
>> their parent
>> + * tables. The IOTLB/devTLBs should be flushed if any PDE/PTEs are cleared.
>> + */
>> +static void switch_to_super_page(struct dmar_domain *domain,
>> +                                unsigned long start_pfn,
>> +                                unsigned long end_pfn, int level) {
> 
> Maybe "swith_to" will lead people to think "remove old and then setup new", so how about something like "remove_room_for_super_page" or "prepare_for_super_page" ?

I named it like this because we also want to have a opposite operation
split_from_super_page() which switch a PDE or PDPE from super page
setting up to small pages, which is needed to optimize dirty bit
tracking during VM live migration.

> 
>> +       unsigned long lvl_pages = lvl_to_nr_pages(level);
>> +       struct dma_pte *pte = NULL;
>> +       int i;
>> +
>> +       while (start_pfn <= end_pfn) {
> 
> start_pfn < end_pfn ?

end_pfn is inclusive.

> 
>> +               if (!pte)
>> +                       pte = pfn_to_dma_pte(domain, start_pfn, &level);
>> +
>> +               if (dma_pte_present(pte)) {
>> +                       dma_pte_free_pagetable(domain, start_pfn,
>> +                                              start_pfn + lvl_pages - 1,
>> +                                              level + 1);
>> +
>> +                       for_each_domain_iommu(i, domain)
>> +                               iommu_flush_iotlb_psi(g_iommus[i],
>> domain,
>> +                                                     start_pfn,
>> lvl_pages,
>> +                                                     0, 0);
>> +               }
>> +
>> +               pte++;
>> +               start_pfn += lvl_pages;
>> +               if (first_pte_in_page(pte))
>> +                       pte = NULL;
>> +       }
>> +}
>> +
>>    static int
>>    __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
>>                    unsigned long phys_pfn, unsigned long nr_pages, int prot)
>> @@ -2341,22 +2376,11 @@ __domain_mapping(struct dmar_domain *domain,
>> unsigned long iov_pfn,
>>                                   return -ENOMEM;
>>                           /* It is large page*/
>>                           if (largepage_lvl > 1) {
>> -                               unsigned long nr_superpages, end_pfn;
>> +                               unsigned long end_pfn;
>>
>>                                   pteval |= DMA_PTE_LARGE_PAGE;
>> -                               lvl_pages = lvl_to_nr_pages(largepage_lvl);
>> -
>> -                               nr_superpages = nr_pages / lvl_pages;
>> -                               end_pfn = iov_pfn + nr_superpages *
>> lvl_pages - 1;
>> -
>> -                               /*
>> -                                * Ensure that old small page tables are
>> -                                * removed to make room for superpage(s).
>> -                                * We're adding new large pages, so make
>> sure
>> -                                * we don't remove their parent tables.
>> -                                */
>> -                               dma_pte_free_pagetable(domain, iov_pfn,
>> end_pfn,
>> -                                                      largepage_lvl +
>> 1);
>> +                               end_pfn = ((iov_pfn + nr_pages) &
>> level_mask(largepage_lvl)) - 1;
>> +                               switch_to_super_page(domain, iov_pfn,
>> end_pfn, largepage_lvl);
>>                           } else {
>>                                   pteval &=
>> ~(uint64_t)DMA_PTE_LARGE_PAGE;
>>                           }
>>
>> I will send you the diff patch off list. Any thoughts?
>>
> 
> The solution looks good to me.
> 
> It's free for you to send this patch if you want, I'll send V2 if you have no plan to send it :)

Please go ahead with a new version. Thank you for catching this and
managing to fix it.

Best regards,
baolu

> 
>> Best regards,
>> baolu
>>
>>>
>>>>> +					int i;
>>>>> +
>>>>> +					dma_pte_free_pagetable(domain, iov_pfn, end_pfn,
>>>>> +							       largepage_lvl + 1);
>>>>> +					for_each_domain_iommu(i, domain)
>>>>> +						iommu_flush_iotlb_psi(g_iommus[i], domain,
>>>>> +								      iov_pfn, nr_pages, 0, 0);
>>>>> +
>>>>
>>>> Best regards,
>>>> baolu

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