Re: swiotlb cleanups v3

[Tom Lendacky <thomas.lendacky@amd.com>]

On 4/20/21 4:23 AM, Christoph Hellwig wrote:
> On Sat, Apr 17, 2021 at 11:39:22AM -0500, Tom Lendacky wrote:
>> Somewhere between the 1st and 2nd patch, specifying a specific swiotlb
>> for an SEV guest is no longer honored. For example, if I start an SEV
>> guest with 16GB of memory and specify swiotlb=131072 I used to get a
>> 256MB SWIOTLB. However, after the 2nd patch, the swiotlb=131072 is no
>> longer honored and I get a 982MB SWIOTLB (as set via sev_setup_arch() in
>> arch/x86/mm/mem_encrypt.c).
>>
>> I can't be sure which patch caused the issue since an SEV guest fails to
>> boot with the 1st patch but can boot with the 2nd patch, at which point
>> the SWIOTLB comes in at 982MB (I haven't had a chance to debug it and so
>> I'm hoping you might be able to quickly spot what's going on).
> 
> Can you try this patch?

Thanks, Christoph. This works for honoring the command line value with SEV
guests.

There was still a reference to default_nslabs in setup_io_tlb_npages()
that I'm not sure how you want to handle. I just commented it out for now
to let the code compile to test the intent of the patch.

Thanks,
Tom

> 
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 0a5b6f7e75bce6..ac81ef97df32f5 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -71,15 +71,17 @@ struct io_tlb_mem *io_tlb_default_mem;
>   */
>  static unsigned int max_segment;
>  
> -static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;
> +static unsigned long swiotlb_cmdline_size;
>  
>  static int __init
>  setup_io_tlb_npages(char *str)
>  {
>  	if (isdigit(*str)) {
>  		/* avoid tail segment of size < IO_TLB_SEGSIZE */
> -		default_nslabs =
> -			ALIGN(simple_strtoul(str, &str, 0), IO_TLB_SEGSIZE);
> +		unsigned long nslabs = simple_strtoul(str, &str, 0);
> +
> +		swiotlb_cmdline_size =
> +			ALIGN(nslabs, IO_TLB_SEGSIZE) << IO_TLB_SHIFT;
>  	}
>  	if (*str == ',')
>  		++str;
> @@ -108,7 +110,9 @@ void swiotlb_set_max_segment(unsigned int val)
>  
>  unsigned long swiotlb_size_or_default(void)
>  {
> -	return default_nslabs << IO_TLB_SHIFT;
> +	if (swiotlb_cmdline_size)
> +		return swiotlb_cmdline_size;
> +	return IO_TLB_DEFAULT_SIZE;
>  }
>  
>  void __init swiotlb_adjust_size(unsigned long size)
> @@ -118,9 +122,10 @@ void __init swiotlb_adjust_size(unsigned long size)
>  	 * architectures such as those supporting memory encryption to
>  	 * adjust/expand SWIOTLB size for their use.
>  	 */
> -	size = ALIGN(size, IO_TLB_SIZE);
> -	default_nslabs = ALIGN(size >> IO_TLB_SHIFT, IO_TLB_SEGSIZE);
> -	pr_info("SWIOTLB bounce buffer size adjusted to %luMB", size >> 20);
> +	if (!swiotlb_cmdline_size)
> +		swiotlb_cmdline_size = ALIGN(size, IO_TLB_SIZE);
> +	pr_info("SWIOTLB bounce buffer size adjusted to %luMB",
> +		swiotlb_cmdline_size >> 20);
>  }
>  
>  void swiotlb_print_info(void)
> @@ -209,7 +214,7 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
>  void  __init
>  swiotlb_init(int verbose)
>  {
> -	size_t bytes = PAGE_ALIGN(default_nslabs << IO_TLB_SHIFT);
> +	size_t bytes = PAGE_ALIGN(swiotlb_size_or_default());
>  	void *tlb;
>  
>  	if (swiotlb_force == SWIOTLB_NO_FORCE)
> @@ -219,7 +224,7 @@ swiotlb_init(int verbose)
>  	tlb = memblock_alloc_low(bytes, PAGE_SIZE);
>  	if (!tlb)
>  		goto fail;
> -	if (swiotlb_init_with_tbl(tlb, default_nslabs, verbose))
> +	if (swiotlb_init_with_tbl(tlb, bytes >> IO_TLB_SHIFT, verbose))
>  		goto fail_free_mem;
>  	return;
>  
> 
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