linux-kernel - Re: [PATCH] iommu/vt-d: Fix identity map bounds in si_domain

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Message-ID: <b3401333-76d3-415a-b2e4-b148c44b13f3@linux.intel.com>
Date: Wed, 10 Jul 2024 10:43:00 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jon Pan-Doh <pandoh@...gle.com>, David Woodhouse <dwmw2@...radead.org>,
 Kevin Tian <kevin.tian@...el.com>
Cc: baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 "H. Peter Anvin" <hpa@...ux.intel.com>, Tejun Heo <tj@...nel.org>,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Sudheer Dantuluri <dantuluris@...gle.com>, Gary Zibrat <gzibrat@...gle.com>
Subject: Re: [PATCH] iommu/vt-d: Fix identity map bounds in si_domain_init()

On 7/10/24 7:49 AM, Jon Pan-Doh wrote:
> Intel IOMMU operates on inclusive bounds (both generally aas well as
> iommu_domain_identity_map()). Meanwhile, for_each_mem_pfn_range() uses
> exclusive bounds for end_pfn. This creates an off-by-one error when
> switching between the two.
> 
> Fixes: 5dfe8660a3d7 ("bootmem: Replace work_with_active_regions() with for_each_mem_pfn_range()")
> Signed-off-by: Jon Pan-Doh<pandoh@...gle.com>
> Tested-by: Sudheer Dantuluri<dantuluris@...gle.com>

Do you mind telling me on which platform did you test this fix? My
understanding is that modern VT-d hardware supports hardware pass
through mode, hence this piece of code won't be executed anymore.

> Suggested-by: Gary Zibrat<gzibrat@...gle.com>
> ---
>   drivers/iommu/intel/iommu.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index fd11a080380c..f55ec1fd7942 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -2071,7 +2071,7 @@ static int __init si_domain_init(int hw)
>   		for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) {
>   			ret = iommu_domain_identity_map(si_domain,
>   					mm_to_dma_pfn_start(start_pfn),
> -					mm_to_dma_pfn_end(end_pfn));
> +					mm_to_dma_pfn_end(end_pfn-1));
>   			if (ret)
>   				return ret;
>   		}

Thanks,
baolu