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

[Samiullah Khawaja <skhawaja@google.com>]

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