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

Hi Baolu,

-----Original Message----- From: Lu Baolu [mailto:baolu.lu@linux.intel.com] Sent: Friday, April 2, 2021 12:44 PM To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.) longpeng2@huawei.com; iommu@lists.linux-foundation.org; linux-kernel@vger.kernel.org Cc: baolu.lu@linux.intel.com; David Woodhouse dwmw2@infradead.org; Nadav Amit nadav.amit@gmail.com; Alex Williamson alex.williamson@redhat.com; Kevin Tian kevin.tian@intel.com; Gonglei (Arei) arei.gonglei@huawei.com; stable@vger.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 ) or NOT-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 ?

...

• 			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