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

[Randy Dunlap]

On 08/24/2018 09:25 AM, Thiago Jung Bauermann wrote:
> From: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
> 
> 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.
> 
> Signed-off-by: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>
> ---
>  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"

I would add a "range" to limit (restrict) how small or large that can be.  E.g.:

	range 16 102400

or even smaller for the maximum value...

> +       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;
> 


-- 
~Randy