[PATCH v5 10/20] dma-direct: make dma_direct_map_phys() honor DMA_ATTR_CC_SHARED

[Michael Kelley]

From: Aneesh Kumar K.V (Arm) <aneesh.kumar at kernel.org> Sent: Thursday, May 21, 2026 9:28 PM
> 
> Teach dma_direct_map_phys() to select the DMA address encoding based on
> DMA_ATTR_CC_SHARED.
> 
> Use phys_to_dma_unencrypted() for decrypted mappings and
> phys_to_dma_encrypted() otherwise. If a device requires unencrypted DMA
> but the source physical address is still encrypted, force the mapping
> through swiotlb so the DMA address and backing memory attributes remain
> consistent.
> 
> Update the arm64, x86, s390 and powerpc secure-guest setup to not use
> swiotlb force option
> 
> Tested-by: Jiri Pirko <jiri at nvidia.com>
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar at kernel.org>
> ---
> Changes from v3:
> * Handle DMA_ATTR_MMIO
> ---
>  arch/arm64/mm/init.c                 |  4 +--
>  arch/powerpc/platforms/pseries/svm.c |  2 +-
>  arch/s390/mm/init.c                  |  2 +-
>  arch/x86/kernel/pci-dma.c            |  4 +--
>  kernel/dma/direct.c                  |  4 ++-
>  kernel/dma/direct.h                  | 45 +++++++++++++++-------------
>  6 files changed, 31 insertions(+), 30 deletions(-)
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index c1b223e7cc8e..a087ac5b15f7 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -340,10 +340,8 @@ void __init arch_mm_preinit(void)
>  	unsigned int flags = SWIOTLB_VERBOSE;
>  	bool swiotlb = max_pfn > PFN_DOWN(arm64_dma_phys_limit);
> 
> -	if (is_realm_world()) {
> +	if (is_realm_world())
>  		swiotlb = true;
> -		flags |= SWIOTLB_FORCE;
> -	}
> 
>  	if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb)
> {
>  		/*
> diff --git a/arch/powerpc/platforms/pseries/svm.c
> b/arch/powerpc/platforms/pseries/svm.c
> index 384c9dc1899a..7a403dbd35ee 100644
> --- a/arch/powerpc/platforms/pseries/svm.c
> +++ b/arch/powerpc/platforms/pseries/svm.c
> @@ -29,7 +29,7 @@ static int __init init_svm(void)
>  	 * need to use the SWIOTLB buffer for DMA even if dma_capable() says
>  	 * otherwise.
>  	 */
> -	ppc_swiotlb_flags |= SWIOTLB_ANY | SWIOTLB_FORCE;
> +	ppc_swiotlb_flags |= SWIOTLB_ANY;
> 
>  	/* Share the SWIOTLB buffer with the host. */
>  	swiotlb_update_mem_attributes();
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index ad3c6d92b801..581af1483c42 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -163,7 +163,7 @@ static void __init pv_init(void)
>  	virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc);
> 
>  	/* make sure bounce buffers are shared */
> -	swiotlb_init(true, SWIOTLB_FORCE | SWIOTLB_VERBOSE);
> +	swiotlb_init(true, SWIOTLB_VERBOSE);
>  	swiotlb_update_mem_attributes();
>  }
> 
> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
> index 6267363e0189..75cf8f6ae8cd 100644
> --- a/arch/x86/kernel/pci-dma.c
> +++ b/arch/x86/kernel/pci-dma.c
> @@ -59,10 +59,8 @@ static void __init pci_swiotlb_detect(void)
>  	 * bounce buffers as the hypervisor can't access arbitrary VM memory
>  	 * that is not explicitly shared with it.
>  	 */
> -	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
> +	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
>  		x86_swiotlb_enable = true;
> -		x86_swiotlb_flags |= SWIOTLB_FORCE;
> -	}

With this patch removing SWIOTLB_FORCE from four places in
kernel code, there are no remaining places where it is set.
The test of SWIOTLB_FORCE could be removed from
swiotlb_init_remap(), and its definition could be deleted
from include/linux/swiotlb.h.

Michael