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

[Alan.Robinson@xxxxxxxxxxx (Alan Robinson)]

Hi Christoph,

On Mon, Apr 04, 2022 at 05:05:56AM +0000, Christoph Hellwig wrote:
> From: Christoph Hellwig <hch@xxxxxx>
> Subject: [PATCH 12/15] swiotlb: provide swiotlb_init variants that remap
>  the buffer
> 
> To shared more code between swiotlb and xen-swiotlb, offer a
> swiotlb_init_remap interface and add a remap callback to
> swiotlb_init_late that will allow Xen to remap the buffer the

s/the buffer//

> buffer without duplicating much of the logic.

Alan

> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  arch/x86/pci/sta2x11-fixup.c |  2 +-
>  include/linux/swiotlb.h      |  5 ++++-
>  kernel/dma/swiotlb.c         | 36 +++++++++++++++++++++++++++++++++---
>  3 files changed, 38 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/pci/sta2x11-fixup.c b/arch/x86/pci/sta2x11-fixup.c
> index c7e6faf59a861..7368afc039987 100644
> --- a/arch/x86/pci/sta2x11-fixup.c
> +++ b/arch/x86/pci/sta2x11-fixup.c
> @@ -57,7 +57,7 @@ static void sta2x11_new_instance(struct pci_dev *pdev)
>               int size = STA2X11_SWIOTLB_SIZE;
>               /* First instance: register your own swiotlb area */
>               dev_info(&pdev->dev, "Using SWIOTLB (size %i)\n", size);
> -             if (swiotlb_init_late(size, GFP_DMA))
> +             if (swiotlb_init_late(size, GFP_DMA, NULL))
>                       dev_emerg(&pdev->dev, "init swiotlb failed\n");
>       }
>       list_add(&instance->list, &sta2x11_instance_list);
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index ee655f2e4d28b..7b50c82f84ce9 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -36,8 +36,11 @@ struct scatterlist;
>  
>  int swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, unsigned int 
> flags);
>  unsigned long swiotlb_size_or_default(void);
> +void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
> +     int (*remap)(void *tlb, unsigned long nslabs));
> +int swiotlb_init_late(size_t size, gfp_t gfp_mask,
> +     int (*remap)(void *tlb, unsigned long nslabs));
>  extern int swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs);
> -int swiotlb_init_late(size_t size, gfp_t gfp_mask);
>  extern void __init swiotlb_update_mem_attributes(void);
>  
>  phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, phys_addr_t phys,
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 119187afc65ec..d5fe8f5e08300 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -256,9 +256,11 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned 
> long nslabs,
>   * Statically reserve bounce buffer space and initialize bounce buffer data
>   * structures for the software IO TLB used to implement the DMA API.
>   */
> -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 +273,23 @@ 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));
> +
> +             nslabs = ALIGN(nslabs >> 1, IO_TLB_SEGSIZE);
> +             if (nslabs < IO_TLB_MIN_SLABS)
> +                     panic("%s: Failed to remap %zu bytes\n",
> +                           __func__, bytes);
> +             goto retry;
> +     }
>       if (swiotlb_init_with_tbl(tlb, default_nslabs, flags))
>               goto fail_free_mem;
>       return;
> @@ -287,12 +300,18 @@ void __init swiotlb_init(bool addressing_limit, 
> unsigned int flags)
>       pr_warn("Cannot allocate buffer");
>  }
>  
> +void __init swiotlb_init(bool addressing_limit, unsigned int flags)
> +{
> +     return swiotlb_init_remap(addressing_limit, flags, NULL);
> +}
> +
>  /*
>   * Systems with larger DMA zones (those that don't support ISA) can
>   * initialize the swiotlb later using the slab allocator if needed.
>   * This should be just like above, but with some error catching.
>   */
> -int swiotlb_init_late(size_t size, gfp_t gfp_mask)
> +int swiotlb_init_late(size_t size, gfp_t gfp_mask,
> +             int (*remap)(void *tlb, unsigned long nslabs))
>  {
>       unsigned long nslabs = ALIGN(size >> IO_TLB_SHIFT, IO_TLB_SEGSIZE);
>       unsigned long bytes;
> @@ -303,6 +322,7 @@ 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;
> @@ -323,6 +343,16 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask)
>                       (PAGE_SIZE << order) >> 20);
>               nslabs = SLABS_PER_PAGE << order;
>       }
> +     if (remap)
> +             rc = remap(vstart, nslabs);
> +     if (rc) {
> +             free_pages((unsigned long)vstart, order);
> + 
> +             nslabs = ALIGN(nslabs >> 1, IO_TLB_SEGSIZE);
> +             if (nslabs < IO_TLB_MIN_SLABS)
> +                     return rc;
> +             goto retry;
> +     }
>       rc = swiotlb_late_init_with_tbl(vstart, nslabs);
>       if (rc)
>               free_pages((unsigned long)vstart, order);
> -- 
> 2.30.2
>