linux-kernel - Re: [PATCH] iommu/vt-d: set INTEL_IOMMU_FLOPPY_WA depend on BLK_DEV

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Message-ID: <8cc26739-99bf-46bb-bf33-90b4ad0052c0@linux.intel.com>
Date: Tue, 18 Nov 2025 09:42:09 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Vineeth Pillai (Google)" <vineeth@...byteword.org>
Cc: dmaluka@...gle.com, shraash@...gle.com, efremov@...ux.com,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: set INTEL_IOMMU_FLOPPY_WA depend on
 BLK_DEV_FD

On 10/3/25 00:16, Vineeth Pillai (Google) wrote:
> INTEL_IOMMU_FLOPPY_WA workaround was introduced to create direct mappings
> for first 16MB for floppy devices as the floppy drivers were not using
> dma apis. We need not do this direct map if floppy driver is not
> enabled.
> 
> INTEL_IOMMU_FLOPPY_WA is generally not a good idea. Iommu will be
> mapping pages in this address range while kernel would also be
> allocating from this range(mostly on memory stress). A misbehaving
> device using this domain will have access to the pages that the
> kernel might be actively using. We noticed this while running a test
> that was trying to figure out if any pages used by kernel is in iommu
> page tables.
> 
> This patch reduces the scope of the above issue by disabling the
> workaround when floppy driver is not enabled. But we would still need to
> fix the floppy driver to use dma apis so that we need not do direct map
> without reserving the pages. Or the other option is to reserve this
> memory range in firmware so that kernel will not use the pages.
> 
> Fixes: d850c2ee5fe22 ("iommu/vt-d: Expose ISA direct mapping region via iommu_get_resv_regions")
> Fixes: 49a0429e53f2 ("Intel IOMMU: Iommu floppy workaround")
> 
> Signed-off-by: Vineeth Pillai (Google)<vineeth@...byteword.org>
> ---
>   drivers/iommu/intel/Kconfig | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Queued for v6.19-rc1. Thanks!