Re: [PATCH] iommu/vt-d: fix system hang on reboot -f

[Ethan Zhao]

在 2025/2/24 9:02, Baolu Lu 写道:
> On 2/20/25 18:15, Yunhui Cui wrote:
> > When entering intel_iommu_shutdown, system interrupts are disabled,
> > and the reboot process might be scheduled out by down_write(). If the
> > scheduled process does not yield (e.g., while(1)), the system will hang.
> >
> > Signed-off-by: Yunhui Cui<cuiyunhui@xxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/intel/iommu.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index cc46098f875b..76a1d83b46bf 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -2871,7 +2871,8 @@ void intel_iommu_shutdown(void)
> >       if (no_iommu || dmar_disabled)
> >           return;
> >   -    down_write(&dmar_global_lock);

Only BSP is running at this point, no DMAR concurrency access protection is needed
anyore, even there is interrupt (only legacy & NMI) coming in, it is impossible to for
scheduler to run any other iommu access code.**
Thanks,
Ethan**

> > +    if (!down_write_trylock(&dmar_global_lock))
> > +        return;
>
> If system interrupts are disabled here, locking is unnecessary. Hotplug
> operations depend on interrupt events, so it's better to remove the
> lock. The shutdown helper then appears like this:
>
> void intel_iommu_shutdown(void)
> {
>         struct dmar_drhd_unit *drhd;
>         struct intel_iommu *iommu = NULL;
>
>         if (no_iommu || dmar_disabled)
>                 return;
>
>         /*
>          * System interrupts are disabled when it reaches here. Locking
>          * is unnecessary when iterating the IOMMU list.
>          */
>         list_for_each_entry(drhd, &dmar_drhd_units, list) {
>                 if (drhd->ignored)
>                         continue;
>
>                 iommu = drhd->iommu;
>                 /* Disable PMRs explicitly here. */
>                 iommu_disable_protect_mem_regions(iommu);
>                 iommu_disable_translation(iommu);
>         }
> }
>
> Does it work for you?
>
> Thanks,
> baolu
--
"firm, enduring, strong, and long-lived"