Re: [PATCH v11 06/11] iommu/arm-smmu-v3: Add ARM_SMMU_OPT_KDUMP_ADOPT for kdump kernel

[Nicolin Chen <nicolinc@nvidia.com>]

On Tue, Oct 20, 2026 at 10:36:04AM -0700, Nicolin Chen wrote:
> On Tue, Oct 20, 2026 at 11:38:21AM +0000, Mostafa Saleh wrote:
> > On Mon, Oct 05, 2026 at 12:30:49PM -0700, Nicolin Chen wrote:
> > > +	/*
> > > +	 * According to spec (6.3.24), HW aligns the base down to the table size
> > > +	 * and ignores the low bits, so an unaligned base would make this kernel
> > > +	 * read a different table.
> > > +	 */
> > > +	if (!IS_ALIGNED(base, size)) {
> > > +		dev_err(smmu->dev, "unaligned stream table base %pa\n", &base);
> > 
> > I understand these are best effort, but what happens if the address
> > corrupted and happens to be aligned?
> 
> This is a basic sanity so HW wouldn't immediately fail. A corrupted
> address would be trickier to test out; also we don't have a perfect
> way to do that. Earlier versions had some address range check. I've
> dropped it, following Jason's comments.
> 
> This is also in the kdocs of the whole smmu kdump functions:
> 
>  *  - Only a coherent SMMU (ARM_SMMU_FEAT_COHERENCY) is supported, as the stream
>  *    table adoption is done by memremap with MEMREMAP_WB, which is verified on
>  *    the real hardware. Callers of these functions are responsible for gating
>  *    ARM_SMMU_FEAT_COHERENCY once during the probe.
>  */

Oops. I copied a wrong paragraph. Should be:

 *  - Values read from the crashed kernel's registers get structural validation
 *    only (format, size, span, alignment, and ID range); the physical addresses
 *    are not vetted, as the kdump kernel has no record of which pages held the
 *    tables.

Thanks
Nicolin