Re: [RFC PATCH 0/5] iommu/arm-smmu-v3: Implement Runtime/System Sleep ops

[Pranjal Shrivastava <praan@google.com>]

On Fri, Mar 21, 2025 at 12:30:34PM -0300, Jason Gunthorpe wrote:
> On Fri, Mar 21, 2025 at 02:44:09PM +0000, Pranjal Shrivastava wrote:
> 
> > However, still there's a worry about the reset value of GBPA.Abort as
> > pointed out by Robin earlier. Since the reset value of GBPA.Abort is 
> > implementation defined.. there's a chance that after a power cycle the
> > SMMU wakes up with GBPA configured to bypass.. in such a case, I don't
> > think the kernel should be responsible to ensure security..
> 
> The kernel should be responsible to operate that HW in a secure
> way. If the spec doesn't guarentee security then you will need a
> ACPI/DT flag to indicate if specific implementations are secure or
> not (ie if the implementation preserves GBPA.Abort).
> 
> Otherwise we'd have to architect around the insecurity somehow and
> prevent the SMMU from unpowering if there is any security sensitive
> attachment..

I see.. and what shall we do based on that ACPI/DT flag? 
Disable pm-runtime for security reasons? That way, the implementations
would get to chose if they *deliberately* want to enable runtime pm
despite the security issues. It can also act as an additional switch for
the pm feature.

> 
> Jason

Thanks,
Praan