RE: [PATCH 05/12] iommu/vt-d: Unncessary spinlock for root table alloc and free

Tian, Kevin
2022-06-01T09:06:05Z

> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Friday, May 27, 2022 2:30 PM
>
> The IOMMU root table is allocated and freed in the IOMMU initialization
> code in static boot or hot-plug paths. There's no need for a spinlock.

s/hot-plug/hot-remove/

>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

> ---
> drivers/iommu/intel/iommu.c | 18 +++++-------------
> 1 file changed, 5 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index bbdd3417a1b1..2d5f02b85de8 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -809,14 +809,12 @@ static int device_context_mapped(struct
> intel_iommu *iommu, u8 bus, u8 devfn)
>
> static void free_context_table(struct intel_iommu *iommu)
> {
> - int i;
> - unsigned long flags;
> struct context_entry *context;
> + int i;
> +
> + if (!iommu->root_entry)
> + return;
>
> - spin_lock_irqsave(&iommu->lock, flags);
> - if (!iommu->root_entry) {
> - goto out;
> - }
> for (i = 0; i < ROOT_ENTRY_NR; i++) {
> context = iommu_context_addr(iommu, i, 0, 0);
> if (context)
> @@ -828,12 +826,10 @@ static void free_context_table(struct intel_iommu
> *iommu)
> context = iommu_context_addr(iommu, i, 0x80, 0);
> if (context)
> free_pgtable_page(context);
> -
> }
> +
> free_pgtable_page(iommu->root_entry);
> iommu->root_entry = NULL;
> -out:
> - spin_unlock_irqrestore(&iommu->lock, flags);
> }
>
> #ifdef CONFIG_DMAR_DEBUG
> @@ -1232,7 +1228,6 @@ static void domain_unmap(struct dmar_domain
> *domain, unsigned long start_pfn,
> static int iommu_alloc_root_entry(struct intel_iommu *iommu)
> {
> struct root_entry *root;
> - unsigned long flags;
>
> root = (struct root_entry *)alloc_pgtable_page(iommu->node);
> if (!root) {
> @@ -1242,10 +1237,7 @@ static int iommu_alloc_root_entry(struct
> intel_iommu *iommu)
> }
>
> __iommu_flush_cache(iommu, root, ROOT_SIZE);
> -
> - spin_lock_irqsave(&iommu->lock, flags);
> iommu->root_entry = root;
> - spin_unlock_irqrestore(&iommu->lock, flags);
>
> return 0;
> }
> --
> 2.25.1