Re: [PATCH RFCv2 07/13] iommufd: Implement sw_msi support natively

On Tue, Jan 14, 2025 at 11:21:13PM -0500, Yury Norov wrote:

...

+static int iommufd_sw_msi_install(struct iommufd_ctx *ictx,

• 		  struct iommufd_hwpt_paging *hwpt_paging,
  

• 		  struct iommufd_sw_msi_map *msi_map)
  

+{

• unsigned long iova;
• lockdep_assert_held(&ictx->sw_msi_lock);
• iova = msi_map->sw_msi_start + msi_map->pgoff * PAGE_SIZE;
• if (!test_bit(msi_map->id, hwpt_paging->present_sw_msi.bitmap)) {

• int rc;
  

• rc = iommu_map(hwpt_paging->common.domain, iova,
  

• 	       msi_map->msi_addr, PAGE_SIZE,
  

• 	       IOMMU_WRITE | IOMMU_READ | IOMMU_MMIO,
  

• 	       GFP_KERNEL_ACCOUNT);
  

• if (rc)
  

• 	return rc;
  

• set_bit(msi_map->id, hwpt_paging->present_sw_msi.bitmap);
  

• }
• return 0;

+}

So, does sw_msi_lock protect the present_sw_msi bitmap? If so, you should use non-atomic __set_bit().

Yes, that is a good point

Thanks, Jason