[PATCH] swiotlb: manipulate orig_addr when tlb_addr has offset

[PATCH] swiotlb: manipulate orig_addr when tlb_addr has offset

[Chanho Park]

From: Bumyong Lee <bumyong.lee@samsung.com>

in case of driver wants to sync part of ranges with offset,
swiotlb_tbl_sync_single() copies from orig_addr base to tlb_addr with offset
it makes data mismatch

it removed from "swiotlb: don't modify orig_addr in swiotlb_tbl_sync_single",
but it have to be recovered

1. Get dma_addr_t from dma_map_single()
dma_addr_t tlb_addr = dma_map_single(dev, vaddr, vsize, DMA_TO_DEVICE);

    |<---------------vsize------------->|
    +-----------------------------------+
    |                                   | original buffer
    +-----------------------------------+
  vaddr

 swiotlb_align_offset
     |<----->|<---------------vsize------------->|
     +-------+-----------------------------------+
     |       |                                   | swiotlb buffer
     +-------+-----------------------------------+
          tlb_addr

2. Do something
3. Sync dma_addr_t through dma_sync_single_for_device(..)
dma_sync_single_for_device(dev, tlb_addr + offset, size, DMA_TO_DEVICE);

  Error case.
    copy data to original buffer.
    but it is from base addr in original buffer

     |<----->|<- offset ->|<- size ->|
     +-------+-----------------------------------+
     |       |            |##########|           | swiotlb buffer
     +-------+-----------------------------------+
          tlb_addr

 swiotlb_align_offset
     |<----->|<- offset ->|<- size ->|
     +-------+-----------------------------------+
     |       |            |##########|           | swiotlb buffer
     +-------+-----------------------------------+
          tlb_addr

    |<- size ->|
    +-----------------------------------+
    |##########|                        | original buffer
    +-----------------------------------+
  vaddr

  FIX. copy data to original buffer.
  but it is from base addr in original buffer

 swiotlb_align_offset
     |<----->|<- offset ->|<- size ->|
     +-------+-----------------------------------+
     |       |            |##########|           | swiotlb buffer
     +-------+-----------------------------------+
          tlb_addr

    |<- offset ->|<- size ->|
    +-----------------------------------+
    |            |##########|           | original buffer
    +-----------------------------------+
  vaddr

Fixes: 16fc3cef33a0 ("swiotlb: don't modify orig_addr in swiotlb_tbl_sync_single")
Signed-off-by: Bumyong Lee <bumyong.lee@samsung.com>
Signed-off-by: Chanho Park <chanho61.park@samsung.com>
---
 kernel/dma/swiotlb.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 8ca7d505d61c..e8243725e298 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -334,6 +334,7 @@ void __init swiotlb_exit(void)
 	io_tlb_default_mem = NULL;
 }
 
+static unsigned int swiotlb_align_offset(struct device *dev, u64 addr);
 /*
  * Bounce: copy the swiotlb buffer from or back to the original dma location
  */
@@ -346,10 +347,17 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
 	size_t alloc_size = mem->slots[index].alloc_size;
 	unsigned long pfn = PFN_DOWN(orig_addr);
 	unsigned char *vaddr = phys_to_virt(tlb_addr);
+	unsigned int tlb_offset;
 
 	if (orig_addr == INVALID_PHYS_ADDR)
 		return;
 
+	tlb_offset = (unsigned int)tlb_addr & (IO_TLB_SIZE - 1);
+	tlb_offset -= swiotlb_align_offset(dev, orig_addr);
+
+	orig_addr += tlb_offset;
+	alloc_size -= tlb_offset;
+
 	if (size > alloc_size) {
 		dev_WARN_ONCE(dev, 1,
 			"Buffer overflow detected. Allocation size: %zu. Mapping size: %zu.\n",
-- 
2.31.1

Re: [PATCH] swiotlb: manipulate orig_addr when tlb_addr has offset

[Christoph Hellwig]

On Mon, May 10, 2021 at 05:30:57PM +0900, Chanho Park wrote:
> +static unsigned int swiotlb_align_offset(struct device *dev, u64 addr);

Please just move swiotlb_align_offset up to avoid the forward declaration.

>  /*
>   * Bounce: copy the swiotlb buffer from or back to the original dma location
>   */
> @@ -346,10 +347,17 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
>  	size_t alloc_size = mem->slots[index].alloc_size;
>  	unsigned long pfn = PFN_DOWN(orig_addr);
>  	unsigned char *vaddr = phys_to_virt(tlb_addr);
> +	unsigned int tlb_offset;
>  
>  	if (orig_addr == INVALID_PHYS_ADDR)
>  		return;
>  
> +	tlb_offset = (unsigned int)tlb_addr & (IO_TLB_SIZE - 1);
> +	tlb_offset -= swiotlb_align_offset(dev, orig_addr);

Nit: I'd write this as:

	tlb_offset = (tlb_addr & (IO_TLB_SIZE - 1)) -
			swiotlb_align_offset(dev, orig_addr);

as there is no need for the cast, and just having a single assignment
is easier to follow.

RE: [PATCH] swiotlb: manipulate orig_addr when tlb_addr has offset

[Chanho Park]

(RESEND due to wrong encrypted message setting)

Hi,

> On Mon, May 10, 2021 at 05:30:57PM +0900, Chanho Park wrote:
> > +static unsigned int swiotlb_align_offset(struct device *dev, u64
> > +addr);
> 
> Please just move swiotlb_align_offset up to avoid the forward declaration.

Okay. I'll move the position of the function next patch.

> 
> >  /*
> >   * Bounce: copy the swiotlb buffer from or back to the original dma
> location
> >   */
> > @@ -346,10 +347,17 @@ static void swiotlb_bounce(struct device *dev,
> phys_addr_t tlb_addr, size_t size
> >  	size_t alloc_size = mem->slots[index].alloc_size;
> >  	unsigned long pfn = PFN_DOWN(orig_addr);
> >  	unsigned char *vaddr = phys_to_virt(tlb_addr);
> > +	unsigned int tlb_offset;
> >
> >  	if (orig_addr == INVALID_PHYS_ADDR)
> >  		return;
> >
> > +	tlb_offset = (unsigned int)tlb_addr & (IO_TLB_SIZE - 1);
> > +	tlb_offset -= swiotlb_align_offset(dev, orig_addr);
> 
> Nit: I'd write this as:
> 
> 	tlb_offset = (tlb_addr & (IO_TLB_SIZE - 1)) -
> 			swiotlb_align_offset(dev, orig_addr);
> 
> as there is no need for the cast, and just having a single assignment is
> easier to follow.

Great. It can be a single assignment as you suggested.

Best Regards,
Chanho Park