Re: [PATCH v2 11/16] iommu/vt-d: preserve PASID table of preserved device

[Pranjal Shrivastava <praan@google.com>]

On Mon, Apr 27, 2026 at 05:56:28PM +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      |   5 +-
>  drivers/iommu/intel/iommu.h      |  12 +++
>  drivers/iommu/intel/liveupdate.c | 141 +++++++++++++++++++++++++++++++
>  drivers/iommu/intel/pasid.c      |   7 +-
>  drivers/iommu/intel/pasid.h      |   9 ++
>  include/linux/kho/abi/iommu.h    |  13 +++
>  6 files changed, 184 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index b90757164cd8..6d42051dcf7c 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -2951,8 +2951,10 @@ static int clear_unpreserve_context_entry_fn(struct device *dev,
>  	if (!info)
>  		return 0;
>  
> -	if (dev_is_pci(dev) && dev_iommu_preserved_state(dev))
> +	if (dev_is_pci(dev) && dev_iommu_preserved_state(dev)) {
> +		pasid_cleanup_preserved_table(dev);
>  		return 0;
> +	}
>  
>  	domain_context_clear(info);
>  	return 0;
> @@ -4013,6 +4015,7 @@ const struct iommu_ops intel_iommu_ops = {
>  	.page_response		= intel_iommu_page_response,
>  #ifdef CONFIG_IOMMU_LIVEUPDATE
>  	.preserve_device	= intel_iommu_preserve_device,
> +	.unpreserve_device	= intel_iommu_unpreserve_device,
>  	.preserve		= intel_iommu_preserve,
>  	.unpreserve		= intel_iommu_unpreserve,
>  #endif
> diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
> index 8e37acf7de12..62076a1a0b4d 100644
> --- a/drivers/iommu/intel/iommu.h
> +++ b/drivers/iommu/intel/iommu.h
> @@ -1290,12 +1290,15 @@ static inline int iopf_for_domain_replace(struct iommu_domain *new,
>  #ifdef CONFIG_IOMMU_LIVEUPDATE
>  int intel_iommu_preserve_device(struct device *dev,
>  				struct iommu_device_ser *device_ser);
> +void intel_iommu_unpreserve_device(struct device *dev,
> +				   struct iommu_device_ser *device_ser);
>  int intel_iommu_preserve(struct iommu_device *iommu,
>  			 struct iommu_hw_ser *iommu_ser);
>  void intel_iommu_unpreserve(struct iommu_device *iommu,
>  			    struct iommu_hw_ser *iommu_ser);
>  void intel_iommu_liveupdate_restore_root_table(struct intel_iommu *iommu,
>  					       struct iommu_hw_ser *iommu_ser);
> +void pasid_cleanup_preserved_table(struct device *dev);
>  #else
>  static inline int intel_iommu_preserve_device(struct device *dev,
>  					      struct iommu_device_ser *device_ser)
> @@ -1303,6 +1306,11 @@ static inline int intel_iommu_preserve_device(struct device *dev,
>  	return -EOPNOTSUPP;
>  }
>  
> +static inline void intel_iommu_unpreserve_device(struct device *dev,
> +						 struct iommu_device_ser *device_ser)
> +{
> +}
> +
>  static inline int intel_iommu_preserve(struct iommu_device *iommu,
>  				       struct iommu_hw_ser *iommu_ser)
>  {
> @@ -1318,6 +1326,10 @@ static inline void intel_iommu_liveupdate_restore_root_table(struct intel_iommu
>  							     struct iommu_hw_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 50a63812533f..404b485e97b9 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_table(struct intel_iommu *iommu, int end)
> @@ -140,10 +141,96 @@ void intel_iommu_liveupdate_restore_root_table(struct intel_iommu *iommu,
>  	iommu_for_each_preserved_device(_restore_used_domain_ids, iommu);
>  }
>  
> +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);

Nit: This is making me consider renaming the helper as
`iommu_preserve_folio`. I almost thought why are we preserving a single
page. 

> +		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;
> +}
> +

[snip]

> +
> +void pasid_cleanup_preserved_table(struct device *dev)
> +{
> +	struct pasid_table *pasid_table;
> +	struct pasid_dir_entry *dir;
> +	struct pasid_entry *table;
> +	size_t dir_size;
> +
> +	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;
> +
> +	/* Clear everything except the first entry in table. */
> +	memset(&table[1], 0, SZ_4K - sizeof(*table));

Nit: Is the first entry always 4K or could it change based on PAGE_SIZE?

> +
> +	/* Use the folio order to calculate the size of Pasid Directory */
> +	dir_size = (1 << (folio_order(virt_to_folio(dir)) + PAGE_SHIFT));
> +
> +	/* Clear everything except the first entry in directory */
> +	memset(&dir[1], 0, dir_size - sizeof(struct pasid_dir_entry));
> +
> +	clflush_cache_range(&table[0], SZ_4K);
> +	clflush_cache_range(&dir[0], dir_size);
> +}
> +

[...]

> +void *intel_pasid_try_restore_table(struct device *dev, u64 max_pasid)
> +{
> +	struct iommu_device_ser *ser = dev_iommu_restored_state(dev);
> +
> +	if (!ser)
> +		return NULL;
> +
> +	BUG_ON(pasid_lu_handle_pd(phys_to_virt(ser->intel.pasid_table),
> +				  PASID_LU_OP_RESTORE));
> +	if (WARN_ON_ONCE(ser->intel.max_pasid != max_pasid)) {

I'm wondering if this could be slightly relaxed to:
if (ser->intel.max_pasid < max_pasid) to ensure it's a minimum
requirement rather than an exact match?

> +		pasid_lu_handle_pd(phys_to_virt(ser->intel.pasid_table),
> +				   PASID_LU_OP_FREE);
> +		return NULL;
> +	}
> +
> +	return phys_to_virt(ser->intel.pasid_table);
> +}
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index 89541b74ab8c..5cac8e95f73b 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ b/drivers/iommu/intel/pasid.c
> @@ -60,8 +60,11 @@ int intel_pasid_alloc_table(struct device *dev)
>  
>  	size = max_pasid >> (PASID_PDE_SHIFT - 3);
>  	order = size ? get_order(size) : 0;
> -	dir = iommu_alloc_pages_node_sz(info->iommu->node, GFP_KERNEL,
> -					1 << (order + PAGE_SHIFT));
> +
> +	dir = intel_pasid_try_restore_table(dev, 1 << (order + PAGE_SHIFT + 3));
> +	if (!dir)
> +		dir = iommu_alloc_pages_node_sz(info->iommu->node, GFP_KERNEL,
> +						1 << (order + PAGE_SHIFT));
>  	if (!dir) {
>  		kfree(pasid_table);
>  		return -ENOMEM;

Thanks,
Praan