Thanks for detail sharing Ard! I think dma-ranges is good enough for payload for now. Thanks, Chasel > -----Original Message----- > From: Ard Biesheuvel <ardb@xxxxxxxxxx> > Sent: Tuesday, November 21, 2023 10:41 AM > To: Chiu, Chasel <chasel.chiu@xxxxxxxxx> > Cc: Simon Glass <sjg@xxxxxxxxxxxx>; Tan, Lean Sheng > <sheng.tan@xxxxxxxxxxxxx>; Devicetree Discuss <devicetree@xxxxxxxxxxxxxxx>; > Rob Herring <robh@xxxxxxxxxx>; Guo, Gua <gua.guo@xxxxxxxxx>; Dong, Guo > <guo.dong@xxxxxxxxx>; Brune, Maximilian <maximilian.brune@xxxxxxxxxxxxx> > Subject: Re: DMA not supported below 4GB > > On Tue, 21 Nov 2023 at 12:47, Chiu, Chasel <chasel.chiu@xxxxxxxxx> wrote: > > > > > > Hi Ard, > > > > I'm not familiar with how dma-ranges will be utilized, could you educate me > more? > > For example, PlatformInit may assign dma-ranges = <0 0x100000000> // 0 ~ > 4GB, but we still want to prevent DMA access from some sensitive regions within > this huge range. > > dma-ranges is typically used to describe how DMA addresses map to CPU physical > addresses, (i.e., how the interconnect is wired up) and consists of a series of <cpu > addr, dma addr, size> triplets describing which regions are valid and how they are > translated. > > I suppose it would be possible to omit some otherwise accessible RAM regions > from this description, but it will only prevent the DMA software layer from using > the region, which it shouldn't be doing anyway if it is not available for allocation. > IOW, the device will still be capable of DMA'ing into the memory if the hardware > permits it. > > > Does that mean we rely on reserved-memory node to prevent DMA from some > regions? > > /reserved-memory prevents RAM from being used to allocate DMA buffers, but it > does not prevent a device driver from creating DMA transactions that access this > memory. > > > Or are there any other nodes that PlatformInit/Payload has to provide? > > > > If you want to prevent DMA access to sensitive RAM regions, you need an > IOMMU, in which case you need to set dma-ranges appropriately for the DT node > that describes the IOMMU, and everything else is managed by the IOMMU driver. > > If you don't have a IOMMU, playing with 'dma-ranges' is only going to give you a > false sense of security (IMHO), given that it does not prevent the hardware from > accessing the memory. (e.g., any DMA capable device using descriptors in RAM > could be tricked into accessing the memory when such a descriptor gets > corrupted) > > > > > > -----Original Message----- > > > From: Simon Glass <sjg@xxxxxxxxxxxx> > > > Sent: Tuesday, November 21, 2023 9:38 AM > > > To: Ard Biesheuvel <ardb@xxxxxxxxxx> > > > Cc: Tan, Lean Sheng <sheng.tan@xxxxxxxxxxxxx>; Devicetree Discuss > > > <devicetree@xxxxxxxxxxxxxxx>; Rob Herring <robh@xxxxxxxxxx>; Guo, > > > Gua <gua.guo@xxxxxxxxx>; Chiu, Chasel <chasel.chiu@xxxxxxxxx>; Dong, > > > Guo <guo.dong@xxxxxxxxx>; Brune, Maximilian > > > <maximilian.brune@xxxxxxxxxxxxx> > > > Subject: Re: DMA not supported below 4GB > > > > > > Hi Ard, > > > > > > On Tue, 21 Nov 2023 at 10:31, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > > > > > > > dma-ranges is supposed to handle this, but I'm not sure how well > > > > it > > > interoperates with SMMUs (which remap DMA addresses into a virtual > > > address space, and this can both solve and create issues when it > > > comes to DMA address limits). > > > > > > > > Adding a 'no-dma-above-4g' property is a bad idea. Not only does > > > > it result in potential inconsistencies wrt 'dma-ranges', it also > > > > only describes 32 bits of DMA addressing capability, and other DMA > > > > addressing limits exist too (40 bits is also common) > > > > > > OK, thank you for that. We will use dma-ranges for this. > > > > > > Regards, > > > Simon > > > > > > > > > > > > > > > > > > > > > > > On Tue, 21 Nov 2023 at 12:01, Lean Sheng Tan > > > > <sheng.tan@xxxxxxxxxxxxx> > > > wrote: > > > >> > > > >> Added Ard for some input on this. > > > >> > > > >> Best Regards, > > > >> Lean Sheng Tan > > > >> > > > >> > > > >> > > > >> 9elements GmbH, Kortumstraße 19-21, 44787 Bochum, Germany > > > >> Email: sheng.tan@xxxxxxxxxxxxx > > > >> Phone: +49 234 68 94 188 > > > >> Mobile: +49 176 76 113842 > > > >> > > > >> Registered office: Bochum > > > >> Commercial register: Amtsgericht Bochum, HRB 17519 > > > >> Management: Sebastian German, Eray Bazaar > > > >> > > > >> Data protection information according to Art. 13 GDPR > > > >> > > > >> > > > >> On Tue, 14 Nov 2023 at 23:17, Simon Glass <sjg@xxxxxxxxxxxx> wrote: > > > >>> > > > >>> Hi, > > > >>> > > > >>> Some devices do not support DMA above 4GB. Is there a way to > > > >>> express this in the devicetree? > > > >>> > > > >>> Should we add sometimes a 'no-dma-above-4g' property? > > > >>> > > > >>> Or should we be using dma-ranges for this? > > > >>> > > > >>> Regards, > > > >>> Simon > > > >>>
