Re: [PATCH v2] iommu/vt-d: Force to flush iotlb before creating superpage

Lu Baolu
2021-04-15T05:59:18Z

Hi Longpeng,

On 4/15/21 8:46 AM, Longpeng(Mike) wrote:
> The translation caches may preserve obsolete data when the
> mapping size is changed, suppose the following sequence which
> can reveal the problem with high probability.
>
> 1.mmap(4GB,MAP_HUGETLB)
> 2.
> while (1) {
> (a) DMA MAP 0,0xa0000
> (b) DMA UNMAP 0,0xa0000
> (c) DMA MAP 0,0xc0000000
> * DMA read IOVA 0 may failure here (Not present)
> * if the problem occurs.
> (d) DMA UNMAP 0,0xc0000000
> }
>
> The page table(only focus on IOVA 0) after (a) is:
> PML4: 0x19db5c1003 entry:0xffff899bdcd2f000
> PDPE: 0x1a1cacb003 entry:0xffff89b35b5c1000
> PDE: 0x1a30a72003 entry:0xffff89b39cacb000
> PTE: 0x21d200803 entry:0xffff89b3b0a72000
>
> The page table after (b) is:
> PML4: 0x19db5c1003 entry:0xffff899bdcd2f000
> PDPE: 0x1a1cacb003 entry:0xffff89b35b5c1000
> PDE: 0x1a30a72003 entry:0xffff89b39cacb000
> PTE: 0x0 entry:0xffff89b3b0a72000
>
> The page table after (c) is:
> PML4: 0x19db5c1003 entry:0xffff899bdcd2f000
> PDPE: 0x1a1cacb003 entry:0xffff89b35b5c1000
> PDE: 0x21d200883 entry:0xffff89b39cacb000 (*)
>
> Because the PDE entry after (b) is present, it won't be
> flushed even if the iommu driver flush cache when unmap,
> so the obsolete data may be preserved in cache, which
> would cause the wrong translation at end.
>
> However, we can see the PDE entry is finally switch to
> 2M-superpage mapping, but it does not transform
> to 0x21d200883 directly:
>
> 1. PDE: 0x1a30a72003
> 2. __domain_mapping
> dma_pte_free_pagetable
> Set the PDE entry to ZERO
> Set the PDE entry to 0x21d200883
>
> So we must flush the cache after the entry switch to ZERO
> to avoid the obsolete info be preserved.
>
> Cc: David Woodhouse <dwmw2@infradead.org>
> Cc: Lu Baolu <baolu.lu@linux.intel.com>
> Cc: Nadav Amit <nadav.amit@gmail.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Kevin Tian <kevin.tian@intel.com>
> Cc: Gonglei (Arei) <arei.gonglei@huawei.com>
>
> Fixes: 6491d4d02893 ("intel-iommu: Free old page tables before creating superpage")
> Cc: <stable@vger.kernel.org> # v3.0+
> Link: https://lore.kernel.org/linux-iommu/670baaf8-4ff8-4e84-4be3-030b95ab5a5e@huawei.com/
> Suggested-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
> ---
> v1 -> v2:
> - add Joerg
> - reconstruct the solution base on the Baolu's suggestion
> ---
> drivers/iommu/intel/iommu.c | 52 +++++++++++++++++++++++++++++++++------------
> 1 file changed, 38 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index ee09323..881c9f2 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -2289,6 +2289,41 @@ 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)
> @@ -2329,22 +2364,11 @@ static inline int hardware_largepage_caps(struct dmar_domain *domain,
> 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;
> }
>

Thank you!

Acked-by: Lu Baolu <baolu.lu@linux.intel.com>

Best regards,
baolu