6.18-stable review patch. If anyone has any objections, please let me know.
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From: Vineeth Pillai (Google) vineeth@bitbyteword.org
[ Upstream commit cb3db5a39e2a6b6396df1780d39a250f649d2e3a ]
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: d850c2ee5fe2 ("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@bitbyteword.org Link: https://lore.kernel.org/r/20251002161625.1155133-1-vineeth@bitbyteword.org Signed-off-by: Lu Baolu baolu.lu@linux.intel.com Signed-off-by: Joerg Roedel joerg.roedel@amd.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/iommu/intel/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig index f2f538c706503..17a91f881b2e9 100644 --- a/drivers/iommu/intel/Kconfig +++ b/drivers/iommu/intel/Kconfig @@ -66,7 +66,7 @@ config INTEL_IOMMU_DEFAULT_ON
config INTEL_IOMMU_FLOPPY_WA def_bool y - depends on X86 + depends on X86 && BLK_DEV_FD help Floppy disk drivers are known to bypass DMA API calls thereby failing to work when IOMMU is enabled. This