On Fri, Jul 26, 2019 at 7:57 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > On Fri, Jul 26, 2019 at 06:00:57AM -0400, Suganath Prabu wrote: > > Although SAS3 & SAS3.5 IT HBA controllers support > > 64-bit DMA addressing, as per hardware design, > > DMA address with all 64-bits set (0xFFFFFFFF-FFFFFFFF) > > results in a firmware fault. > > Linux will never send a dma address with all bits set anyway, as that > is our magic escape for the dma_addr_t error value. Additionally to > generate that address you'd need a 1-byte sized, 1-byte aligned buffer, > which we never use. I agree with your above statement. But it is also possible that 0xFFFFFFFF-FFFFFFFF falls under the DMA able range, e.g. SGE's start address is 0xFFFFFFFF-FFFF000 and data length is 0x1000 bytes. So when HBA tries to DMA the data at 0xFFFFFFFF-FFFFFFFF location then it will faults the firmware due to it's hardware design. We have observed above example's SGE address and length on AMD systems with SME & IOMMU enabled. Thanks, Sreekanth
