Re: [RESEND PATCH 1/2] dma/pool: Use vmap() address for memory encryption helpers on ARM64

[Shanker Donthineni]

Hi Catalin,

On 8/11/25 12:26, Catalin Marinas wrote:
> External email: Use caution opening links or attachments
>
>
> On Sun, Aug 10, 2025 at 07:50:34PM -0500, Shanker Donthineni wrote:
> > In atomic_pool_expand(), set_memory_encrypted()/set_memory_decrypted()
> > are currently called with page_to_virt(page). On ARM64 with
> > CONFIG_DMA_DIRECT_REMAP=y, the atomic pool is mapped via vmap(), so
> > page_to_virt(page) does not reference the actual mapped region.
> >
> > Using this incorrect address can cause encryption attribute updates to
> > be applied to the wrong memory region. On ARM64 systems with memory
> > encryption enabled (e.g. CCA), this can lead to data corruption or
> > crashes.
> >
> > Fix this by using the vmap() address ('addr') on ARM64 when invoking
> > the memory encryption helpers, while retaining the existing
> > page_to_virt(page) usage for other architectures.
> >
> > Fixes: 76a19940bd62 ("dma-direct: atomic allocations must come from atomic coherent pools")
> > Signed-off-by: Shanker Donthineni <sdonthineni@xxxxxxxxxx>
> > ---
> >   kernel/dma/pool.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> > index 7b04f7575796b..ba08a301590fd 100644
> > --- a/kernel/dma/pool.c
> > +++ b/kernel/dma/pool.c
> > @@ -81,6 +81,7 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
> >   {
> >        unsigned int order;
> >        struct page *page = NULL;
> > +     void *vaddr;
> >        void *addr;
> >        int ret = -ENOMEM;
> >
> > @@ -113,8 +114,8 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
> >         * Memory in the atomic DMA pools must be unencrypted, the pools do not
> >         * shrink so no re-encryption occurs in dma_direct_free().
> >         */
> > -     ret = set_memory_decrypted((unsigned long)page_to_virt(page),
> > -                                1 << order);
> > +     vaddr = IS_ENABLED(CONFIG_ARM64) ? addr : page_to_virt(page);
> > +     ret = set_memory_decrypted((unsigned long)vaddr, 1 << order);
>
> At least with arm CCA, there are two aspects to setting the memory
> encrypted/decrypted: an RMM (realm management monitor) call and setting
> of the attributes of the stage 1 mapping. The RMM call doesn't care
> about the virtual address, only the (intermediate) physical address, so
> having page_to_virt(page) here is fine.
>
> The second part is setting the (fake) attribute for this mapping (top
> bit of the IPA space). Can we not instead just call:
>
>          addr = dma_common_contiguous_remap(page, pool_size,
>                                             pgprot_decrypted(pgprot_dmacoherent(PAGE_KERNEL)),
>                                             __builtin_return_address(0));
Thanks for the simple fix, it resolves the crash issue. I’ve
posted the v2 patch and dropped patch 2/2 which was added to
support non-linear memory regions in pageattr.c.

> in the atomic pool code? The advantage is that we keep the
> set_memory_decrypted() call on the linear map so that we change its
> attributes as well.
>
> I want avoid walking the page tables for vmap regions if possible in the
> arm64 set_memory_* implementation. At some point I was proposing a
> GFP_DECRYPTED flag for allocations but never got around to post a patch
> (and implement vmalloc() support):
>
> https://lore.kernel.org/linux-arm-kernel/ZmNJdSxSz-sYpVgI@xxxxxxx/
>
> --
> Catalin