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Message-ID: <c9abca62-328d-d0d6-a8a6-a67475171f92@arm.com>
Date: Fri, 23 Apr 2021 12:34:31 +0100
From: Steven Price <steven.price@....com>
To: Claire Chang <tientzu@...omium.org>,
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Subject: Re: [PATCH v5 05/16] swiotlb: Add restricted DMA pool initialization
On 22/04/2021 09:14, Claire Chang wrote:
> Add the initialization function to create restricted DMA pools from
> matching reserved-memory nodes.
>
> Signed-off-by: Claire Chang <tientzu@...omium.org>
> ---
> include/linux/device.h | 4 +++
> include/linux/swiotlb.h | 3 +-
> kernel/dma/swiotlb.c | 80 +++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 86 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 38a2071cf776..4987608ea4ff 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -416,6 +416,7 @@ struct dev_links_info {
> * @dma_pools: Dma pools (if dma'ble device).
> * @dma_mem: Internal for coherent mem override.
> * @cma_area: Contiguous memory area for dma allocations
> + * @dma_io_tlb_mem: Internal for swiotlb io_tlb_mem override.
> * @archdata: For arch-specific additions.
> * @of_node: Associated device tree node.
> * @fwnode: Associated device node supplied by platform firmware.
> @@ -521,6 +522,9 @@ struct device {
> #ifdef CONFIG_DMA_CMA
> struct cma *cma_area; /* contiguous memory area for dma
> allocations */
> +#endif
> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> + struct io_tlb_mem *dma_io_tlb_mem;
> #endif
> /* arch specific additions */
> struct dev_archdata archdata;
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index 216854a5e513..03ad6e3b4056 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -72,7 +72,8 @@ 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/swiotlb.c b/kernel/dma/swiotlb.c
> index 57a9adb920bf..ffbb8724e06c 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -39,6 +39,13 @@
> #ifdef CONFIG_DEBUG_FS
> #include <linux/debugfs.h>
> #endif
> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> +#include <linux/io.h>
> +#include <linux/of.h>
> +#include <linux/of_fdt.h>
> +#include <linux/of_reserved_mem.h>
> +#include <linux/slab.h>
> +#endif
>
> #include <asm/io.h>
> #include <asm/dma.h>
> @@ -681,3 +688,76 @@ static int __init swiotlb_create_default_debugfs(void)
> late_initcall(swiotlb_create_default_debugfs);
>
> #endif
> +
> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> +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;
> +
> + if (dev->dma_io_tlb_mem)
> + return 0;
> +
> + /* 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) {
> + mem = kzalloc(struct_size(mem, slots, nslabs), GFP_KERNEL);
> + if (!mem)
> + return -ENOMEM;
> +#ifdef CONFIG_ARM
> + if (!PageHighMem(pfn_to_page(PHYS_PFN(rmem->base)))) {
> + kfree(mem);
> + return -EINVAL;
> + }
> +#endif /* CONFIG_ARM */
> + swiotlb_init_io_tlb_mem(mem, rmem->base, nslabs, false);
> +
> + rmem->priv = mem;
> + }
> +
> +#ifdef CONFIG_DEBUG_FS
> + if (!io_tlb_default_mem->debugfs)
> + io_tlb_default_mem->debugfs =
> + debugfs_create_dir("swiotlb", NULL);
At this point it's possible for io_tlb_default_mem to be NULL, leading
to a splat.
But even then if it's not and we have the situation where debugfs==NULL
then the debugfs_create_dir() here will cause a subsequent attempt in
swiotlb_create_debugfs() to fail (directory already exists) leading to
mem->debugfs being assigned an error value. I suspect the creation of
the debugfs directory needs to be separated from io_tlb_default_mem
being set.
Other than that I gave this series a go with our prototype of Arm's
Confidential Computer Architecture[1] - since the majority of the
guest's memory is protected from the host the restricted DMA pool allows
(only) a small area to be shared with the host.
After fixing (well hacking round) the above it all seems to be working
fine with virtio drivers.
Thanks,
Steve
[1]
https://www.arm.com/why-arm/architecture/security-features/arm-confidential-compute-architecture
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