On Wed, Jan 29, 2025 at 02:44:12PM +0100, Eric Auger wrote: > Hi, > > > On 1/11/25 4:32 AM, Nicolin Chen wrote: > > For systems that require MSI pages to be mapped into the IOMMU translation > > the IOMMU driver provides an IOMMU_RESV_SW_MSI range, which is the default > > recommended IOVA window to place these mappings. However, there is nothing > > special about this address. And to support the RMR trick in VMM for nested > well at least it shall not overlap VMM's RAM. So it was not random either. > > translation, the VMM needs to know what sw_msi window the kernel is using. > > As there is no particular reason to force VMM to adopt the kernel default, > > provide a simple IOMMU_OPTION_SW_MSI_START/SIZE ioctl that the VMM can use > > to directly specify the sw_msi window that it wants to use, which replaces > > and disables the default IOMMU_RESV_SW_MSI from the driver to avoid having > > to build an API to discover the default IOMMU_RESV_SW_MSI. > IIUC the MSI window will then be different when using legacy VFIO > assignment and iommufd backend. ? They use the same, iommufd can have userspace override it. Then it will ignore the reserved region. > MSI reserved regions are exposed in > /sys/kernel/iommu_groups/<n>/reserved_regions > 0x0000000008000000 0x00000000080fffff msi > Is that configurability reflected accordingly? ? Nothing using iommufd should parse that sysfs file. > How do you make sure it does not collide with other resv regions? I > don't see any check here. Yes this does need to be checked, it does look missing. It still needs to create a reserved region in the ioas when attaching to keep the areas safe and it has to intersect with the incoming reserved regions from the driver. > > + * @IOMMU_OPTION_SW_MSI_START: > > + * Change the base address of the IOMMU mapping region for MSI doorbell(s). > > + * It must be set this before attaching a device to an IOAS/HWPT, otherwise > > + * this option will be not effective on that IOAS/HWPT. User can choose to > > + * let kernel pick a base address, by simply ignoring this option or setting > > + * a value 0 to IOMMU_OPTION_SW_MSI_SIZE. Global option, object_id must be 0 > I think we should document it cannot be put at a random place either. It can be put at any place a map can be placed. That also needs to be checked when creating a domain, it can't be outside the geometry. Jason
