Re: [PATCH v4 10/18] iommu/vt-d: Restore IOMMU state and reclaimed domain ids

[Baolu Lu]

On 8/28/26 02:47, Samiullah Khawaja wrote:
> > > +/**
> > > + * intel_iommu_liveupdate_restore_root_table() - Restore root table 
> > > and reclaim domain IDs
> > > + * @iommu: Target IOMMU
> > > + * @iommu_ser: Serialized IOMMU hardware state from previous kernel
> > > + *
> > > + * Restores the preserved root table and context tables for the 
> > > IOMMU hardware
> > > + * instance across Live Update, and reclaims all domain IDs 
> > > previously allocated
> > > + * to preserved devices so they are not reused.
> > > + */
> > > +void intel_iommu_liveupdate_restore_root_table(struct intel_iommu 
> > > *iommu,
> > > +                           struct iommu_hw_ser *iommu_ser)
> > > +{
> > > +    if (!iommu_ser->intel.restored)
> > > +        iommu_restore_pages(iommu_ser->intel.root_table);
> > > +
> > > +    iommu->root_entry = __va(iommu_ser->intel.root_table);
> > > +
> > > +    if (!iommu_ser->intel.restored)
> > > +        restore_iommu_context(iommu);
> > > +
> > > +    iommu_ser->intel.restored = 1;
> >
> > This uses iommu_ser->intel.restored to prevent restoring the root and
> > context tables multiple times. For this to work safely, iommu_ser-
> > > intel.restored must be 0 the first time restore runs after kexec.
> >
> > The problem is: this field is inside struct iommu_hw_ser, and that
> > struct is allocated in the old kernel. How to ensure that the previous
> > kernel has zeroed this out? Maybe I’m overthinking this.
>
> This is a valid point. However, the old kernel allocates this struct
> with GFP_ZERO and it never touches the restored field prior to kexec.
> So it should be zero in the new kernel.

That should be fine.

I just found it a bit odd that a variable used only by the incoming
kernel depends on initialization done in the old kernel. :-)

Thanks,
baolu