Re: [PATCH] iommu/vt-d: Force to flush iotlb before creating superpage

[Lu Baolu]

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@xxxxxxxxxxxxxxx]
> > Sent: Friday, April 2, 2021 12:44 PM
> > To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> > <longpeng2@xxxxxxxxxx>; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx;
> > linux-kernel@xxxxxxxxxxxxxxx
> > Cc: baolu.lu@xxxxxxxxxxxxxxx; David Woodhouse <dwmw2@xxxxxxxxxxxxx>; Nadav
> > Amit <nadav.amit@xxxxxxxxx>; Alex Williamson <alex.williamson@xxxxxxxxxx>;
> > Kevin Tian <kevin.tian@xxxxxxxxx>; Gonglei (Arei) <arei.gonglei@xxxxxxxxxx>;
> > stable@xxxxxxxxxxxxxxx
> > 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)
+{
+       unsigned long lvl_pages = lvl_to_nr_pages(level);
+       struct dma_pte *pte = NULL;
+       int i;
+
+       while (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?

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