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Date: Thu, 8 Apr 2021 07:37:48 +0000
From: "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)"
<longpeng2@...wei.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>,
"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: 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 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" ?
> + 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 ?
> + 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 :)
> 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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