On Tue, Aug 24, 2021 at 10:26 PM Guenter Roeck [off-list ref] wrote:

Hi Claire,

On Thu, Jun 24, 2021 at 11:55:24PM +0800, Claire Chang wrote:

quoted

Add the initialization function to create restricted DMA pools from
matching reserved-memory nodes.

Regardless of swiotlb setting, the restricted DMA pool is preferred if
available.

The restricted DMA pools provide a basic level of protection against the
DMA overwriting buffer contents at unexpected times. However, to protect
against general data leakage and system memory corruption, the system
needs to provide a way to lock down the memory access, e.g., MPU.

Signed-off-by: Claire Chang <redacted>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Stefano Stabellini <sstabellini@kernel.org>
Tested-by: Will Deacon <will@kernel.org>
---
 include/linux/swiotlb.h |  3 +-
 kernel/dma/Kconfig      | 14 ++++++++
 kernel/dma/swiotlb.c    | 76 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 92 insertions(+), 1 deletion(-)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 3b9454d1e498..39284ff2a6cd 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h

@@ -73,7 +73,8 @@ extern enum swiotlb_force swiotlb_force;
  *           range check to see if the memory was in fact allocated by this
  *           API.
  * @nslabs:  The number of IO TLB blocks (in groups of 64) between @start and
- *           @end. This is command line adjustable via setup_io_tlb_npages.
+ *           @end. For default swiotlb, this is command line adjustable via
+ *           setup_io_tlb_npages.
  * @used:    The number of used IO TLB block.
  * @list:    The free list describing the number of free entries available
  *           from each index.

diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index 77b405508743..3e961dc39634 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig

@@ -80,6 +80,20 @@ config SWIOTLB
      bool
      select NEED_DMA_MAP_STATE

+config DMA_RESTRICTED_POOL
+     bool "DMA Restricted Pool"
+     depends on OF && OF_RESERVED_MEM
+     select SWIOTLB

This makes SWIOTLB user configurable, which in turn results in

mips64-linux-ld: arch/mips/kernel/setup.o: in function `arch_mem_init':
setup.c:(.init.text+0x19c8): undefined reference to `plat_swiotlb_setup'
make[1]: *** [Makefile:1280: vmlinux] Error 1

when building mips:allmodconfig.

Should this possibly be "depends on SWIOTLB" ?

Patch is sent here: https://lkml.org/lkml/2021/8/26/932

Thanks,
Guenter

Thanks,
Claire