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Subject: Re: [PATCH v15 10/12] swiotlb: Add restricted DMA pool initialization

On Tue, Aug 24, 2021 at 10:26 PM Guenter Roeck <[email protected]> wrote:
>
> Hi Claire,
>
> On Thu, Jun 24, 2021 at 11:55:24PM +0800, Claire Chang wrote:
> > 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 <[email protected]>
> > Reviewed-by: Christoph Hellwig <[email protected]>
> > Tested-by: Stefano Stabellini <[email protected]>
> > Tested-by: Will Deacon <[email protected]>
> > ---
> > 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

2021-08-27 07:01:13

by Andy Shevchenko

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Subject: Re: [PATCH v15 10/12] swiotlb: Add restricted DMA pool initialization

On Thu, Jun 24, 2021 at 6:59 PM Claire Chang <[email protected]> wrote:
>
> 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.

> +static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
> + struct device *dev)
> +{
> + struct io_tlb_mem *mem = rmem->priv;
> + unsigned long nslabs = rmem->size >> IO_TLB_SHIFT;
> +
> + /*
> + * Since multiple devices can share the same pool, the private data,
> + * io_tlb_mem struct, will be initialized by the first device attached
> + * to it.
> + */

> + if (!mem) {

Can it be rather

if (mem)
goto out_assign;

or so?

> + mem = kzalloc(struct_size(mem, slots, nslabs), GFP_KERNEL);
> + if (!mem)
> + return -ENOMEM;
> +
> + set_memory_decrypted((unsigned long)phys_to_virt(rmem->base),
> + rmem->size >> PAGE_SHIFT);

Below you are using a macro from pfn.h, but not here, I think it's PFN_DOWN().

> + swiotlb_init_io_tlb_mem(mem, rmem->base, nslabs, false);
> + mem->force_bounce = true;
> + mem->for_alloc = true;
> +
> + rmem->priv = mem;
> +
> + if (IS_ENABLED(CONFIG_DEBUG_FS)) {
> + mem->debugfs =
> + debugfs_create_dir(rmem->name, debugfs_dir);
> + swiotlb_create_debugfs_files(mem);
> + }
> + }
> +
> + dev->dma_io_tlb_mem = mem;
> +
> + return 0;
> +}
> +
> +static void rmem_swiotlb_device_release(struct reserved_mem *rmem,
> + struct device *dev)
> +{
> + dev->dma_io_tlb_mem = io_tlb_default_mem;
> +}
> +
> +static const struct reserved_mem_ops rmem_swiotlb_ops = {
> + .device_init = rmem_swiotlb_device_init,
> + .device_release = rmem_swiotlb_device_release,
> +};
> +
> +static int __init rmem_swiotlb_setup(struct reserved_mem *rmem)
> +{
> + unsigned long node = rmem->fdt_node;
> +
> + if (of_get_flat_dt_prop(node, "reusable", NULL) ||
> + of_get_flat_dt_prop(node, "linux,cma-default", NULL) ||
> + of_get_flat_dt_prop(node, "linux,dma-default", NULL) ||
> + of_get_flat_dt_prop(node, "no-map", NULL))
> + return -EINVAL;
> +
> + if (PageHighMem(pfn_to_page(PHYS_PFN(rmem->base)))) {
> + pr_err("Restricted DMA pool must be accessible within the linear mapping.");
> + return -EINVAL;
> + }
> +
> + rmem->ops = &rmem_swiotlb_ops;
> + pr_info("Reserved memory: created restricted DMA pool at %pa, size %ld MiB\n",
> + &rmem->base, (unsigned long)rmem->size / SZ_1M);

Oh là là, besides explicit casting that I believe can be avoided, %ld
!= unsigned long. Can you check the printk-formats.rst document?

> + return 0;
> +}
> +
> +RESERVEDMEM_OF_DECLARE(dma, "restricted-dma-pool", rmem_swiotlb_setup);
> #endif /* CONFIG_DMA_RESTRICTED_POOL */

--
With Best Regards,
Andy Shevchenko