Re: [PATCH] iommu/vt-d: Do not dump pasid table entries in kdump kernel

[zelin deng]

在 2022/1/20 上午10:58, Lu Baolu 写道:
> On 1/19/22 5:07 PM, Zelin Deng wrote:
> > In kdump kernel PASID translations won't be copied from previous kernel
> > even if scalable-mode is enabled, so pages of PASID translations are
>
> Yes. The copy table support for scalable mode is still in my task list.
>
> > non-present in kdump kernel. Attempt to access those address will cause
> > PF fault:
> >
> > [   13.396476] DMAR: DRHD: handling fault status reg 3
> > [   13.396478] DMAR: [DMA Read NO_PASID] Request device [81:00.0] 
> > fault addr 0xffffd000 [fault reason 0x59] SM: Present bit in PA$
> > [   13.396480] DMAR: Dump dmar5 table entries for IOVA 0xffffd000
> > [   13.396481] DMAR: scalable mode root entry: hi 0x0000000000000000, 
> > low 0x00000000460d1001
> > [   13.396482] DMAR: context entry: hi 0x0000000000000008, low 
> > 0x00000010c4237401
> > [   13.396485] BUG: unable to handle page fault for address: 
> > ff110010c4237000
> > [   13.396486] #PF: supervisor read access in kernel mode
> > [   13.396487] #PF: error_code(0x0000) - not-present page
> > [   13.396488] PGD 5d201067 P4D 5d202067 PUD 0
> > [   13.396490] Oops: 0000 [#1] PREEMPT SMP NOPTI
> > [   13.396491] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 
> > 5.16.0-rc6-next-20211224+ #6
> > [   13.396493] Hardware name: Intel Corporation 
> > EAGLESTREAM/EAGLESTREAM, BIOS EGSDCRB1.86B.0067.D12.2110190950 
> > 10/19/2021
> > [   13.396494] RIP: 0010:dmar_fault_dump_ptes+0x13b/0x295
> >
> > Hence skip dumping pasid table entries if in kdump kernel.
>
> This just asks dmar_fault_dump_ptes() to keep silent. The problem is
> that the context entry is mis-configured. Perhaps we should disable
> copy table for scalable mode for now. How about below change?

Yep.  The change looks good to me.

Actually I had encountered another issue which had blocked virtio-net 
device when scalable mode is enabled in kdump kernel so that I had made 
the same change as yours -- 'to disable translation if sm_on in kdump 
kernel' in our internal tree.

I only observe this issue on our dragonfly baremetal server with 
virtio-net device inside, I did't send the fix to upstream as I am not 
sure if it is reasonable to disable translation in kdump kernel.


> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -3337,10 +3337,11 @@ static int __init init_dmars(void)
>
>                 init_translation_status(iommu);
>
> -               if (translation_pre_enabled(iommu) && 
> !is_kdump_kernel()) {
> +               if (translation_pre_enabled(iommu) &&
> +                   (!is_kdump_kernel() || sm_supported(iommu))) {
>                         iommu_disable_translation(iommu);
>                         clear_translation_pre_enabled(iommu);
> -                       pr_warn("Translation was enabled for %s but we 
> are not in kdump mode\n",
> +                       pr_warn("Translation was enabled for %s but we 
> are not in kdump mode or copy table not supported\n",
>                                 iommu->name);
>                 }
>
> > Fixes: 914ff7719e8a (“iommu/vt-d: Dump DMAR translation structure 
> > when DMA fault occurs”)
> > Signed-off-by: Zelin Deng <zelin.deng@xxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/intel/iommu.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 92fea3fb..f0134cf 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -1074,6 +1074,12 @@ void dmar_fault_dump_ptes(struct intel_iommu 
> > *iommu, u16 source_id,
> >       if (!sm_supported(iommu))
> >           goto pgtable_walk;
> >   +    /* PASID translations is not copied, skip dumping pasid table 
> > entries
> > +     * otherwise non-present page will be accessed.
> > +     */
> > +    if (is_kdump_kernel())
> > +        goto pgtable_walk;
> > +
> >       /* get the pointer to pasid directory entry */
> >       dir = phys_to_virt(ctx_entry->lo & VTD_PAGE_MASK);
> >       if (!dir) {
>
> Best regards,
> baolu