Re: [RFC PATCH v3 4/5] dma-mapping: Encapsulate memory state during allocation

[Mostafa Saleh <smostafa@google.com>]

On Thu, May 07, 2026 at 06:36:27PM +0100, Catalin Marinas wrote:
> On Fri, Apr 17, 2026 at 03:45:11PM +0000, Mostafa Saleh wrote:
> > On Fri, Apr 10, 2026 at 03:05:04PM -0300, Jason Gunthorpe wrote:
> > > On Wed, Apr 08, 2026 at 07:47:41PM +0000, Mostafa Saleh wrote:
> > > > Introduce a new dma-direct internal type dma_page which is
> > > > "struct page" and a bit indicate whether the memory has been decrypted
> > > > or not.
> > > > This is useful to pass such information encapsulated through
> > > > allocation functions, which is currently set from swiotlb_alloc().
> > > > 
> > > > No functional changes.
> > > > 
> > > > Signed-off-by: Mostafa Saleh <smostafa@google.com>
> > > > ---
> > > >  kernel/dma/direct.c | 58 +++++++++++++++++++++++++++++++++++----------
> > > >  1 file changed, 46 insertions(+), 12 deletions(-)
> > > > 
> > > > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> > > > index de63e0449700..204bc566480c 100644
> > > > --- a/kernel/dma/direct.c
> > > > +++ b/kernel/dma/direct.c
> > > > @@ -16,6 +16,33 @@
> > > >  #include <linux/pci-p2pdma.h>
> > > >  #include "direct.h"
> > > >  
> > > > +/*
> > > > + * Represent DMA allocation and 1 bit flag for it's state
> > > > + */
> > > 
> > > I'd explain this wrappers a pointer and uses the low PAGE_SHIFT bits
> > > for flags..
> > > 
> > > > +struct dma_page {
> > > > +	unsigned long val;
> > > 
> > > unintptr_t ?
> > 
> > I thought about that, but I don’t see unintptr_t anywhere in the
> > kernel, it seems similar cases use “unsigned long” as in xarray.h
> 
> Jason meant uintptr_t. However, we have a similar pattern with struct
> encoded_page as an incomplete type and encode_page() adds the bits
> directly to the pointer. I'd use something similar as there's precedent
> already.

I see, makes sense, I will do that.

Thanks,
Mostafa

> 
> -- 
> Catalin