Hi Peter On 20/06/2025 4:35 pm, Peter Xu wrote: > Caution: External email. Do not open attachments or click links, unless this > email comes from a known sender and you know the content is safe. > > > On Fri, Jun 20, 2025 at 05:56:49AM +0000, CLEMENT MATHIEU--DRIF wrote: >> This short series adds the 'address type' bit (concept from PCIe) to the >> memory attributes and extends the IOMMUAccessFlags enum. This >> will be required to implement ATS support for the virtual IOMMUs. >> >> Address type: Field present in the PCIe R/W requests, it allows devices to >> tell the IOMMU if the address provided in the request is physical or not. >> In other words, it allows the devices to use a physical address obtained >> via ATS and to prevent the IOMMU from trying to remap it on the fly. > > Two pure questions on the flags, could be relevant to spec: > >> >> Additional IOMMU access flags: >> - Execute Requested > > Does this mean that we can start to put code into DMA regions so that > device can run some day (even if the device may have a core that is totally > different arch v.s. the host's AFAIU, the spec is so nonrestrictive about this flag that heterogeneous arch should not be an issue.
"The definition of what it means for a Function to execute code is outside the scope of this specification" > >> - Privileged Mode Requested >> - Global >> - Untranslated Only (cannot be used with 'Address type = translated') > > I can understand this with patch 1, but not yet with patch 2. > > Patch 1 makes sense to me, IIUC it means the addresses to be used in a pcie > request will be translated addresses which should bypass IOMMU DMAR. > > OTOH, patch 2 added it into iotlb access permissions, which I'm not sure > what does it mean. Perhaps those addresses can only be translated by ATS > pre-translation requests, so that DMA on top of them (in IOVA address > space) will directly fail? I put this here because the ATS API returns IOMMUTLBEntry structures, which contain these flags. The untranslated-only bit is set in ATS responses to inform the device that the requested address cannot be pre-translated and should be translated on the fly by the DMA remapping engine. The interrupt range commonly falls into this category. > > Side note, it might still be more reasonable to put these changes into the > ATS series as the first user of flags. Yes, I can do that. However, the ATS series will contain ~10/~12 patches, is it a concern? Thanks >cmd > > Thanks, > >> >> Clement Mathieu--Drif (2): >> pci: Add a memory attribute for pre-translated DMA operations >> memory: Add permissions in IOMMUAccessFlags >> >> include/exec/memattrs.h | 3 +++ >> include/hw/pci/pci.h | 9 +++++++++ >> include/system/memory.h | 23 +++++++++++++++++++++-- >> 3 files changed, 33 insertions(+), 2 deletions(-) >> >> -- >> 2.49.0 >> > > -- > Peter Xu >
