[RFC PATCH 11/11] powerpc/svm: Increase SWIOTLB buffer size

Konrad Rzeszutek Wilk konrad at darnok.org
Tue Aug 28 04:18:31 AEST 2018


On Fri, Aug 24, 2018 at 01:25:35PM -0300, Thiago Jung Bauermann wrote:
> From: Anshuman Khandual <khandual at linux.vnet.ibm.com>
> 
> SWIOTLB buffer default size (64MB) is not enough for large sequential write
> operations which eventually leads to kernel crash like here.
> 
> virtio-pci 0000:00:05.0: swiotlb buffer is full (sz: 327680 bytes)
> virtio-pci 0000:00:05.0: DMA: Out of SW-IOMMU space for 327680 bytes
> Kernel panic - not syncing: DMA: Random memory could be DMA read
> CPU: 12 PID: 3985 Comm: mkfs.ext4 Not tainted 4.18.0-rc4+ #285
> Call Trace:
> [c0000007d2a27020] [c000000000cfdffc] dump_stack+0xb0/0xf4 (unreliable)
> [c0000007d2a27060] [c000000000112a98] panic+0x140/0x328
> [c0000007d2a270f0] [c0000000001b4f88] swiotlb_full+0x108/0x130
> [c0000007d2a27180] [c0000000001b5f6c] swiotlb_map_page+0x25c/0x2c0
> [c0000007d2a271e0] [c0000000007bfaf8] vring_map_one_sg.isra.0+0x58/0x70
> [c0000007d2a27200] [c0000000007c08dc] virtqueue_add_sgs+0x1bc/0x690
> [c0000007d2a272f0] [d0000000042a1280] virtio_queue_rq+0x358/0x4a0 [virtio_blk]
> [c0000007d2a273d0] [c0000000006b5d68] blk_mq_dispatch_rq_list+0x1f8/0x6d0
> ..................
> 
> Increase the SWIOTLB size to 1GB on Ultravisor based secure guests.

Gosh, that is huge.

What about making the SWIOTLB be more dynamic? That is expand it's size
dynamically if it can?

> 
> Signed-off-by: Anshuman Khandual <khandual at linux.vnet.ibm.com>
> Signed-off-by: Thiago Jung Bauermann <bauerman at linux.ibm.com>
> ---
>  arch/powerpc/Kconfig | 5 +++++
>  kernel/dma/swiotlb.c | 5 +++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 1466d1234723..fee7194ce9e4 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -457,6 +457,11 @@ config PPC_SVM
>  
>  	 If unsure, say "N".
>  
> +config SWIOTLB_DEFAULT_SIZE
> +       int "Size of Software I/O TLB buffer (in MiB)"
> +       default "1024"
> +       depends on PPC_SVM
> +
>  config PPC_TRANSACTIONAL_MEM
>         bool "Transactional Memory support for POWERPC"
>         depends on PPC_BOOK3S_64
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 04b68d9dffac..32dc67422d8a 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -146,8 +146,13 @@ void swiotlb_set_max_segment(unsigned int val)
>  		max_segment = rounddown(val, PAGE_SIZE);
>  }
>  
> +#ifdef CONFIG_SWIOTLB_DEFAULT_SIZE
> +#define IO_TLB_DEFAULT_SIZE ((unsigned long) CONFIG_SWIOTLB_DEFAULT_SIZE << 20)
> +#else
>  /* default to 64MB */
>  #define IO_TLB_DEFAULT_SIZE (64UL<<20)
> +#endif
> +
>  unsigned long swiotlb_size_or_default(void)
>  {
>  	unsigned long size;
> 


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