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

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Date:   Fri, 2 Apr 2021 12:44:02 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Longpeng(Mike)" <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.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?

> +					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