| From: Raj, Ashok <ashok.raj@xxxxxxxxx> | Sent: Monday, September 25, 2017 12:03 PM | | On Mon, Sep 25, 2017 at 01:11:04PM -0700, Dan Williams wrote: | > On Mon, Sep 25, 2017 at 1:05 PM, Casey Leedom <leedom@xxxxxxxxxxx> wrote: | > > | From: Dan Williams <dan.j.williams@xxxxxxxxx> | > > | Sent: Monday, September 25, 2017 12:31 PM | > > | ... | > > | IIUC it looks like this has been broken ever since commit e1605495c716 | > > | "intel-iommu: Introduce domain_sg_mapping() to speed up | > > | intel_map_sg()". I.e. it looks like the calculation for pte_val should | > > | be: | > > | | > > | pteval = (page_to_phys(sg_page(sg)) + sg->offset) | prot; | > > | > > Hhmmm, shouldn't that be: | > > | > > pteval = (page_to_phys(sg_page(sg)) + (sg->offset>>PAGE_SHIFT)) | prot; | > | > Yes, I think you're right. We do want to mask off the page-unaligned | > portion of sg->offset. | | Shoulnd't we normalize the entire sg_page(sg) + sg_offset. | | if when you only mask the page-unaligned portion i suspect you might be | pointing to a different region? | | something like (sg_page(sg) + (sg->offset << VTD_PAGE_SHIFT)) | | then add the unaligned part.. sg->offset>>VTD_PAGE_SHIFT | | Is this happening because you are using a 2M page? not sure what triggers | this or causes the driver to get passed in larger than 4K offset, or | running 32bit kernel? | | if its legal to get passed in such odd values, we should fix IOMMU driver to | handle it properly, otherwise we should atleast fail those requests. (woof) This is all above me. I've spent a chunk of time fruitlessly trying to find documentation which says that scatterlist's are allowed to have offset/length values which extend outside the sg_page(sg). So someone much more familiar with this stuff is going to need to say what's allowed. As I said, I've asked Harsh to provide us with a detailed trace of exactly what he's seeing and what the Scatter/Gather Lists are getting translated into. That information may make it easier to understand if/how __domain_mapping() is screwing up ... Casey
