Re: [PATCH v2 10/19] x86, swiotlb: Teach swiotlb to skip "accepted" devices

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Dan Williams <dan.j.williams@intel.com> writes:

> There are two mechanisms to force SWIOTLB operation, the kernel command
> line option and the internal SWIOTLB_FORCE flag. With the arrival of
> "accepted" devices, devices that have been enabled to DMA to private
> encrypted memory, the SWIOTLB_FORCE flag is an awkward fit. It may be the
> case that SWIOTLB operation wants to be forced regardless of the device
> acceptance state.
>
> Introduce a new SWIOTLB_UNACCPTED flag that allows for both augmenting the
> result of is_swiotlb_force_bounce() dynamically and allowing for an "always
> SWIOTLB" override.
>
> Cc: Thomas Gleixner <tglx@kernel.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: x86@kernel.org
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  include/linux/swiotlb.h   | 15 ++++++++++++---
>  arch/x86/kernel/pci-dma.c |  2 +-
>  kernel/dma/swiotlb.c      |  1 +
>  3 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index 3dae0f592063..0efb9b8e5dd0 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -17,6 +17,7 @@ struct scatterlist;
>  #define SWIOTLB_VERBOSE	(1 << 0) /* verbose initialization */
>  #define SWIOTLB_FORCE	(1 << 1) /* force bounce buffering */
>  #define SWIOTLB_ANY	(1 << 2) /* allow any memory for the buffer */
> +#define SWIOTLB_UNACCEPTED (1 << 3) /* swiotlb for unaccepted devices */
>  
>  /*
>   * Maximum allowable number of contiguous slabs to map,
> @@ -91,6 +92,7 @@ struct io_tlb_pool {
>   * @nslabs:	Total number of IO TLB slabs in all pools.
>   * @debugfs:	The dentry to debugfs.
>   * @force_bounce: %true if swiotlb bouncing is forced
> + * @bounce_unaccepted: %true if unaccepted devices must bounce
>   * @for_alloc:  %true if the pool is used for memory allocation
>   * @can_grow:	%true if more pools can be allocated dynamically.
>   * @phys_limit:	Maximum allowed physical address.
> @@ -109,8 +111,9 @@ struct io_tlb_mem {
>  	struct io_tlb_pool defpool;
>  	unsigned long nslabs;
>  	struct dentry *debugfs;
> -	bool force_bounce;
> -	bool for_alloc;
> +	u8 force_bounce:1;
> +	u8 bounce_unaccepted:1;
> +	u8 for_alloc:1;
>  #ifdef CONFIG_SWIOTLB_DYNAMIC
>  	bool can_grow;
>  	u64 phys_limit;
> @@ -173,7 +176,13 @@ static inline bool is_swiotlb_force_bounce(struct device *dev)
>  {
>  	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
>  
> -	return mem && mem->force_bounce;
> +	if (!mem)
> +		return false;
> +	if (mem->force_bounce)
> +		return true;
> +	if (mem->bounce_unaccepted && !device_cc_accepted(dev))
> +		return true;
> +	return false;
>  }
>  
>  void swiotlb_init(bool addressing_limited, unsigned int flags);
> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
> index 6267363e0189..8a737f501ae5 100644
> --- a/arch/x86/kernel/pci-dma.c
> +++ b/arch/x86/kernel/pci-dma.c
> @@ -61,7 +61,7 @@ static void __init pci_swiotlb_detect(void)
>  	 */
>  	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
>  		x86_swiotlb_enable = true;
> -		x86_swiotlb_flags |= SWIOTLB_FORCE;
> +		x86_swiotlb_flags |= SWIOTLB_UNACCEPTED;
>  	}
>  }
>  #else
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index a547c7693135..57e9647939fe 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -365,6 +365,7 @@ void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
>  
>  	io_tlb_default_mem.force_bounce =
>  		swiotlb_force_bounce || (flags & SWIOTLB_FORCE);
> +	io_tlb_default_mem.bounce_unaccepted = flags & SWIOTLB_UNACCEPTED;
>

This should be.

@@ -373,7 +373,7 @@ void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
 
 	io_tlb_default_mem.force_bounce =
 		swiotlb_force_bounce || (flags & SWIOTLB_FORCE);
-	io_tlb_default_mem.bounce_unaccepted = flags & SWIOTLB_UNACCEPTED;
+	io_tlb_default_mem.bounce_unaccepted = !!(flags & SWIOTLB_UNACCEPTED);
 
>  
>  #ifdef CONFIG_SWIOTLB_DYNAMIC
>  	if (!remap)
> -- 
> 2.52.0