Re: [PATCH 12/15] swiotlb: provide swiotlb_init variants that remap the buffer

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 3/14/22 3:31 AM, Christoph Hellwig wrote:
> -void __init swiotlb_init(bool addressing_limit, unsigned int flags)
> +void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
> +		int (*remap)(void *tlb, unsigned long nslabs))
>   {
> -	size_t bytes = PAGE_ALIGN(default_nslabs << IO_TLB_SHIFT);
> +	unsigned long nslabs = default_nslabs;
> +	size_t bytes;
>   	void *tlb;
>   
>   	if (!addressing_limit && !swiotlb_force_bounce)
> @@ -271,12 +273,24 @@ void __init swiotlb_init(bool addressing_limit, unsigned int flags)
>   	 * allow to pick a location everywhere for hypervisors with guest
>   	 * memory encryption.
>   	 */
> +retry:
> +	bytes = PAGE_ALIGN(default_nslabs << IO_TLB_SHIFT);
>   	if (flags & SWIOTLB_ANY)
>   		tlb = memblock_alloc(bytes, PAGE_SIZE);
>   	else
>   		tlb = memblock_alloc_low(bytes, PAGE_SIZE);
>   	if (!tlb)
>   		goto fail;
> +	if (remap && remap(tlb, nslabs) < 0) {
> +		memblock_free(tlb, PAGE_ALIGN(bytes));
> +
> +		/* Min is 2MB */
> +		if (nslabs <= 1024)


This is IO_TLB_MIN_SLABS, isn't it? (Xen code didn't say so but that's what it meant to say I believe)


> +			panic("%s: Failed to remap %zu bytes\n",
> +			      __func__, bytes);
> +		nslabs = max(1024UL, ALIGN(nslabs >> 1, IO_TLB_SEGSIZE));
> +		goto retry;
> +	}
>
> @@ -303,6 +323,7 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask)
>   	if (swiotlb_force_disable)
>   		return 0;
>   
> +retry:
>   	order = get_order(nslabs << IO_TLB_SHIFT);
>   	nslabs = SLABS_PER_PAGE << order;
>   	bytes = nslabs << IO_TLB_SHIFT;
> @@ -317,6 +338,17 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask)
>   
>   	if (!vstart)
>   		return -ENOMEM;
> +	if (remap)
> +		rc = remap(vstart, nslabs);
> +	if (rc) {
> +		free_pages((unsigned long)vstart, order);
> +
> +		/* Min is 2MB */
> +		if (nslabs <= 1024)


Same here.


-boris


> +			return rc;
> +		nslabs = max(1024UL, ALIGN(nslabs >> 1, IO_TLB_SEGSIZE));
> +		goto retry;
> +	}
>   
>   	if (order != get_order(bytes)) {
>   		pr_warn("only able to allocate %ld MB\n",