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

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Date:   Thu, 20 Jan 2022 10:58:48 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Zelin Deng <zelin.deng@...ux.alibaba.com>,
        David Woodhouse <dwmw2@...radead.org>
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: Do not dump pasid table entries in kdump
 kernel

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?

--- 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@...ux.alibaba.com>
> ---
>   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