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

[Jason Gunthorpe]

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