Re: [PATCH v4 2/3] swiotlb: dma: its: Enforce host page-size alignment for shared buffers

[Jason Gunthorpe <jgg@ziepe.ca>]

On Mon, Apr 27, 2026 at 12:01:07PM +0530, Aneesh Kumar K.V (Arm) wrote:
> When running private-memory guests, the guest kernel must apply additional
> constraints when allocating buffers that are shared with the hypervisor.

This patch has way too much stuff in it.

I think your patch structure should be changed around

1) Patch to add mem_decrypt_granule_size(), and explain it as
   the alignment & size of what can be passed to
   set_memory_encrypted/decrypted()

2) Add support for mem_decrypt_granule_size() to ARM

Then patches going caller by caller of set_memory_decrypted() to make
them follow the new rule:

3) its

4) swiotlb 

3) dma_alloc_coherent

etc.

don't forget about the new dma buf heaps too:

drivers/dma-buf/heaps/system_heap.c:    ret = set_memory_decrypted(addr, nr_pages);

It is worth calling out in the cover letter that all the ARM CCA
relevant places are fixed but drivers/hv/ is left for future.

> @@ -33,18 +32,30 @@ int arm64_mem_crypt_ops_register(const struct arm64_mem_crypt_ops *ops)
>  
>  int set_memory_encrypted(unsigned long addr, int numpages)
>  {
> -	if (likely(!crypt_ops) || WARN_ON(!PAGE_ALIGNED(addr)))
> +	if (likely(!crypt_ops))
>  		return 0;
>  
> +	if (WARN_ON(!IS_ALIGNED(addr, mem_decrypt_granule_size())))
> +		return -EINVAL;
> +
> +	if (WARN_ON(!IS_ALIGNED(numpages << PAGE_SHIFT, mem_decrypt_granule_size())))
> +		return -EINVAL;
> +
>  	return crypt_ops->encrypt(addr, numpages);
>  }
>  EXPORT_SYMBOL_GPL(set_memory_encrypted);
>  
>  int set_memory_decrypted(unsigned long addr, int numpages)
>  {
> -	if (likely(!crypt_ops) || WARN_ON(!PAGE_ALIGNED(addr)))
> +	if (likely(!crypt_ops))
>  		return 0;
>  
> +	if (WARN_ON(!IS_ALIGNED(addr, mem_decrypt_granule_size())))
> +		return -EINVAL;
> +
> +	if (WARN_ON(!IS_ALIGNED(numpages << PAGE_SHIFT, mem_decrypt_granule_size())))
> +		return -EINVAL;
> +
>  	return crypt_ops->decrypt(addr, numpages);
>  }
>  EXPORT_SYMBOL_GPL(set_memory_decrypted);

This should go in the ARM patch adding mem_decrypt_granule_size() to CCA

> diff --git a/include/linux/mem_encrypt.h b/include/linux/mem_encrypt.h
> index 07584c5e36fb..1e01c9ac697f 100644
> --- a/include/linux/mem_encrypt.h
> +++ b/include/linux/mem_encrypt.h
> @@ -11,6 +11,8 @@
>  #define __MEM_ENCRYPT_H__
>  
>  #ifndef __ASSEMBLY__
> +#include <linux/align.h>
> +#include <vdso/page.h>
>  
>  #ifdef CONFIG_ARCH_HAS_MEM_ENCRYPT
>  
> @@ -54,6 +56,18 @@
>  #define dma_addr_canonical(x)		(x)
>  #endif
>  
> +#ifndef mem_decrypt_granule_size
> +static inline size_t mem_decrypt_granule_size(void)
> +{
> +	return PAGE_SIZE;
> +}
> +#endif
> +
> +static inline size_t mem_decrypt_align(size_t size)
> +{
> +	return ALIGN(size, mem_decrypt_granule_size());
> +}
> +
>  #endif	/* __ASSEMBLY__ */
>  
>  #endif	/* __MEM_ENCRYPT_H__ */

I know it seems a bit small, but put this in its own patch and explain
how it works. I'd also like to see a kdoc here, and add a kdoc to
set_memory_decrypted() that links back so people have a better chance
to know about this.

Jason