Re: [RFC PATCH v3 1/5] swiotlb: Return state of memory from swiotlb_alloc()

[Mostafa Saleh <smostafa@google.com>]

On Tue, Apr 14, 2026 at 02:55:33PM +0530, Aneesh Kumar K.V wrote:
> Mostafa Saleh <smostafa@google.com> writes:
> 
> > Make swiotlb_alloc() return the state of the allocated memory, at
> > the moment all the pools are decrypted but that would change soon.
> > In the next patches dma-direct will use the returned state to
> > determine whether to decrypt the memory and use the proper memory
> > decryption/encryption related functions.
> >
> > Also, add swiotlb_is_decrypted(), that will be used before calling
> > swiotlb_free() to check whether the memory needs to be encrypted
> > by the caller.
> >
> > Signed-off-by: Mostafa Saleh <smostafa@google.com>
> > ---
> >  include/linux/swiotlb.h | 25 +++++++++++++++++++++++--
> >  kernel/dma/direct.c     |  2 +-
> >  kernel/dma/swiotlb.c    | 23 ++++++++++++++++++++++-
> >  3 files changed, 46 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> > index 3dae0f592063..24be65494ce8 100644
> > --- a/include/linux/swiotlb.h
> > +++ b/include/linux/swiotlb.h
> > @@ -63,6 +63,7 @@ extern void __init swiotlb_update_mem_attributes(void);
> >   * @area_nslabs: Number of slots in each area.
> >   * @areas:	Array of memory area descriptors.
> >   * @slots:	Array of slot descriptors.
> > + * @decrypted:	Whether the pool was decrypted or left in default state.
> >   * @node:	Member of the IO TLB memory pool list.
> >   * @rcu:	RCU head for swiotlb_dyn_free().
> >   * @transient:  %true if transient memory pool.
> > @@ -77,6 +78,7 @@ struct io_tlb_pool {
> >  	unsigned int area_nslabs;
> >  	struct io_tlb_area *areas;
> >  	struct io_tlb_slot *slots;
> > +	bool decrypted;
> >  #ifdef CONFIG_SWIOTLB_DYNAMIC
> >  	struct list_head node;
> >  	struct rcu_head rcu;
> > @@ -281,16 +283,31 @@ static inline void swiotlb_sync_single_for_cpu(struct device *dev,
> >
> 
> Should this be a property of struct io_tlb_mem ? 

I envisioned that this would be mainly used by restricted-dma so in
that case it doesn’t seem to matter.
But generally, I guess it would depend on the discovery mechanism of
this memory property and I can imagine a memory allocator that has
multiple pools with different attributes. So propably it's better to
be per pool.

Thanks,
Mostafa

> 
> -aneesh