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iommu/vt-d: Cache max domain ID to avoid redundant calculation

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The cap_ndoms() helper calculates the maximum available domain ID from
the value of capability register, which can be inefficient if called
repeatedly. Cache the maximum supported domain ID in max_domain_id field
during initialization to avoid redundant calls to cap_ndoms() throughout
the IOMMU driver.

No functionality change.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
This commit is contained in:
Lu Baolu 2026-08-05 07:43:08 +08:00 committed by Joerg Roedel
parent 1c677d8a2c
commit 5b3ba0a002
3 changed files with 7 additions and 5 deletions
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1
drivers/iommu/intel/dmar.c
View File

@ -1174,6 +1174,7 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
spin_lock_init(&iommu->lock);
ida_init(&iommu->domain_ida);
mutex_init(&iommu->did_lock);
iommu->max_domain_id = cap_ndoms(iommu->cap);
ver = readl(iommu->reg + DMAR_VER_REG);
pr_info("%s: reg_base_addr %llx ver %d:%d cap %llx ecap %llx\n",

10
drivers/iommu/intel/iommu.c
View File

@ -1047,7 +1047,7 @@ int domain_attach_iommu(struct dmar_domain *domain, struct intel_iommu *iommu)
}
num = ida_alloc_range(&iommu->domain_ida, IDA_START_DID,
cap_ndoms(iommu->cap) - 1, GFP_KERNEL);
iommu->max_domain_id - 1, GFP_KERNEL);
if (num < 0) {
pr_err("%s: No free domain ids\n", iommu->name);
goto err_unlock;
@ -1111,7 +1111,7 @@ static void copied_context_tear_down(struct intel_iommu *iommu,
did_old = context_domain_id(context);
context_clear_entry(context);
if (did_old < cap_ndoms(iommu->cap)) {
if (did_old < iommu->max_domain_id) {
iommu->flush.flush_context(iommu, did_old,
PCI_DEVID(bus, devfn),
DMA_CCMD_MASK_NOBIT,
@ -1511,7 +1511,7 @@ static int copy_context_table(struct intel_iommu *iommu,
continue;
did = context_domain_id(&ce);
if (did >= 0 && did < cap_ndoms(iommu->cap))
if (did >= 0 && did < iommu->max_domain_id)
ida_alloc_range(&iommu->domain_ida, did, did, GFP_KERNEL);
set_context_copied(iommu, bus, devfn);
@ -2431,7 +2431,7 @@ static ssize_t domains_supported_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct intel_iommu *iommu = dev_to_intel_iommu(dev);
return sysfs_emit(buf, "%ld\n", cap_ndoms(iommu->cap));
return sysfs_emit(buf, "%ld\n", iommu->max_domain_id);
}
static DEVICE_ATTR_RO(domains_supported);
@ -2442,7 +2442,7 @@ static ssize_t domains_used_show(struct device *dev,
unsigned int count = 0;
int id;
for (id = 0; id < cap_ndoms(iommu->cap); id++)
for (id = 0; id < iommu->max_domain_id; id++)
if (ida_exists(&iommu->domain_ida, id))
count++;

1
drivers/iommu/intel/iommu.h
View File

@ -700,6 +700,7 @@ struct intel_iommu {
/* mutex to protect domain_ida */
struct mutex did_lock;
struct ida domain_ida; /* domain id allocator */
unsigned long max_domain_id;
unsigned long *copied_tables; /* bitmap of copied tables */
spinlock_t lock; /* protect context, domain ids */
struct root_entry *root_entry; /* virtual address */