Re: [PATCH 09/14] iommu/vt-d: preserve PASID table of preserved device

Samiullah Khawaja
2026-03-23T18:52:00Z

On Mon, Mar 23, 2026 at 06:19:18PM +0000, Pranjal Shrivastava wrote:
>On Tue, Feb 03, 2026 at 10:09:43PM +0000, Samiullah Khawaja wrote:
>> In scalable mode the PASID table is used to fetch the io page tables.
>> Preserve and restore the PASID table of the preserved devices.
>>
>> Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
>> ---
>> drivers/iommu/intel/iommu.c | 4 +-
>> drivers/iommu/intel/iommu.h | 5 ++
>> drivers/iommu/intel/liveupdate.c | 130 +++++++++++++++++++++++++++++++
>> drivers/iommu/intel/pasid.c | 7 +-
>> drivers/iommu/intel/pasid.h | 9 +++
>> include/linux/kho/abi/iommu.h | 8 ++
>> 6 files changed, 160 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index 83faad53f247..2d0dae57f5a2 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -2944,8 +2944,10 @@ static bool __maybe_clean_unpreserved_context_entries(struct intel_iommu *iommu)
>> if (info->iommu != iommu)
>> continue;
>>
>> - if (dev_iommu_preserved_state(&pdev->dev))
>> + if (dev_iommu_preserved_state(&pdev->dev)) {
>> + pasid_cleanup_preserved_table(&pdev->dev);
>> continue;
>> + }
>>
>> domain_context_clear(info);
>> }
>> diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
>> index 057bd6035d85..d24d6aeaacc0 100644
>> --- a/drivers/iommu/intel/iommu.h
>> +++ b/drivers/iommu/intel/iommu.h
>> @@ -1286,6 +1286,7 @@ int intel_iommu_preserve(struct iommu_device *iommu, struct iommu_ser *iommu_ser
>> void intel_iommu_unpreserve(struct iommu_device *iommu, struct iommu_ser *iommu_ser);
>> void intel_iommu_liveupdate_restore_root_table(struct intel_iommu *iommu,
>> struct iommu_ser *iommu_ser);
>> +void pasid_cleanup_preserved_table(struct device *dev);
>> #else
>> static inline int intel_iommu_preserve_device(struct device *dev, struct device_ser *device_ser)
>> {
>> @@ -1309,6 +1310,10 @@ static inline void intel_iommu_liveupdate_restore_root_table(struct intel_iommu
>> struct iommu_ser *iommu_ser)
>> {
>> }
>> +
>> +static inline void pasid_cleanup_preserved_table(struct device *dev)
>> +{
>> +}
>> #endif
>>
>> #ifdef CONFIG_INTEL_IOMMU_SVM
>> diff --git a/drivers/iommu/intel/liveupdate.c b/drivers/iommu/intel/liveupdate.c
>> index 6dcb5783d1db..53bb5fe3a764 100644
>> --- a/drivers/iommu/intel/liveupdate.c
>> +++ b/drivers/iommu/intel/liveupdate.c
>> @@ -14,6 +14,7 @@
>> #include <linux/pci.h>
>>
>> #include "iommu.h"
>> +#include "pasid.h"
>> #include "../iommu-pages.h"
>>
>> static void unpreserve_iommu_context(struct intel_iommu *iommu, int end)
>> @@ -113,9 +114,89 @@ void intel_iommu_liveupdate_restore_root_table(struct intel_iommu *iommu,
>> iommu->reg_phys, iommu_ser->intel.root_table);
>> }
>>
>> +enum pasid_lu_op {
>> + PASID_LU_OP_PRESERVE = 1,
>> + PASID_LU_OP_UNPRESERVE,
>> + PASID_LU_OP_RESTORE,
>> + PASID_LU_OP_FREE,
>> +};
>> +
>> +static int pasid_lu_do_op(void *table, enum pasid_lu_op op)
>> +{
>> + int ret = 0;
>> +
>> + switch (op) {
>> + case PASID_LU_OP_PRESERVE:
>> + ret = iommu_preserve_page(table);
>> + break;
>> + case PASID_LU_OP_UNPRESERVE:
>> + iommu_unpreserve_page(table);
>> + break;
>> + case PASID_LU_OP_RESTORE:
>> + iommu_restore_page(virt_to_phys(table));
>> + break;
>> + case PASID_LU_OP_FREE:
>> + iommu_free_pages(table);
>> + break;
>> + }
>> +
>> + return ret;
>> +}
>> +
>> +static int pasid_lu_handle_pd(struct pasid_dir_entry *dir, enum pasid_lu_op op)
>> +{
>> + struct pasid_entry *table;
>> + int ret;
>> +
>> + /* Only preserve first table for NO_PASID. */
>> + table = get_pasid_table_from_pde(&dir[0]);
>> + if (!table)
>> + return -EINVAL;
>> +
>> + ret = pasid_lu_do_op(table, op);
>> + if (ret)
>> + return ret;
>> +
>> + ret = pasid_lu_do_op(dir, op);
>> + if (ret)
>> + goto err;
>> +
>> + return 0;
>> +err:
>> + if (op == PASID_LU_OP_PRESERVE)
>> + pasid_lu_do_op(table, PASID_LU_OP_UNPRESERVE);
>> +
>> + return ret;
>> +}
>> +
>> +void pasid_cleanup_preserved_table(struct device *dev)
>> +{
>> + struct pasid_table *pasid_table;
>> + struct pasid_dir_entry *dir;
>> + struct pasid_entry *table;
>> +
>> + pasid_table = intel_pasid_get_table(dev);
>> + if (!pasid_table)
>> + return;
>> +
>> + dir = pasid_table->table;
>> + table = get_pasid_table_from_pde(&dir[0]);
>> + if (!table)
>> + return;
>> +
>> + /* Cleanup everything except the first entry. */
>> + memset(&table[1], 0, SZ_4K - sizeof(*table));
>> + memset(&dir[1], 0, SZ_4K - sizeof(struct pasid_dir_entry));
>
>(Not too familiar with Intel IOMMU / VT-d)
>We seem to hardcode SZ_4K when clearing the directory entries. But in
>intel_pasid_alloc_table(), the allocation size seems to depend on
>max_pasid which could be larger than one page (order > 0)?
>
>If the directory is multi-page, won't we leave the trailing pages
>and full of stale PDE pointers that the HW could still walk?

Agreed. It should cleanup based on max_pasid. Will update.
>
>> +
>> + clflush_cache_range(&table[0], SZ_4K);
>> + clflush_cache_range(&dir[0], SZ_4K);
>> +}
>> +
>
>[ ------ >8 ------ ]
>
>Thanks,
>Praan