* Tony Battersby <tonyb@xxxxxxxxxxxxxxx> [181206 16:13]: > On 12/6/18 10:51 AM, Robin Murphy wrote: > >> Here is the prototype: > >> > >> void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma); > >> > >> With the old code, the 'dma' value had to be correct for use with > >> pool_find_page(), or else you would get an error. If the 'vaddr' value > >> was incorrect, it would corrupt the dmapool freelist, but you wouldn't > >> get an error unless DMAPOOL_DEBUG was enabled. > >> > >> With my patch applied, 'vaddr' has to be correct for virt_to_page(). My > >> code also checks that 'dma' is consistent with 'vaddr' even if > >> DMAPOOL_DEBUG is disabled, since the check is fast and it will prevent > >> problems like this in the future. > > Unfortunately that logic has a fatal flaw - DMA pools are backed by > > dma_alloc_coherent(), and there is absolutely no guarantee that the > > memory dma_alloc_coherent() returns is backed by a struct page at all. > > Even if it is, there is still absolutely no guarantee that the vaddr > > value it returns is valid for virt_to_page() - on many systems it will > > be in vmalloc or some architecture-specific region of address space. > > > > The problem is not that these drivers are buggy (they're not - the arch > > code is returning a vmalloc()ed non-cacheable remap in the first place), > > it's that 26abe88e830d is fundamentally unworkable and needs reverting. > > Apparently the original patches managed not to catch my eye as something > > I needed to review, sorry about that :( > > > > Robin. > > > Thanks for the info; the inner workings of the vm system are a bit out > of my area of expertise. My first version of the patch series used a > different method that didn't rely on virt_to_page(); I will go back to > that version, clean it up, and resubmit when I have time. > > Andrew, please revert all 9 patches. I will resubmit the set when I > have a workable solution. OK sounds good to me. I can test the new set easily when available if you Cc me on them. Thanks, Tony
