On Wed, Aug 25, 2021 at 01:12:37PM +0200, David Hildenbrand wrote: > On 25.08.21 12:55, Catalin Marinas wrote: > > On Wed, Aug 25, 2021 at 12:38:31PM +0200, David Hildenbrand wrote: > > > On 25.08.21 12:20, Catalin Marinas wrote: > > > > I can see the documentation for pfn_valid() does not claim anything more > > > > than the presence of an memmap entry. But I wonder whether the confusion > > > > is wider-spread than just the DMA code. At a quick grep, try_ram_remap() > > > > assumes __va() can be used on pfn_valid(), though I suspect it relies on > > > > the calling function to check that the resource was RAM. The arm64 > > > > kern_addr_valid() returns true based on pfn_valid() and kcore.c uses > > > > standard memcpy on it, which wouldn't work for I/O (should we change > > > > this check to pfn_is_map_memory() for arm64?). > > > > > > kern_addr_valid() checks that there is a direct map entry, and that the > > > mapped address has a valid mmap. (copied from x86-64) > > > > It checks that there is a va->pa mapping, not necessarily in the linear > > map as it walks the page tables. So for some I/O range that happens to > > be mapped but which was in close proximity to RAM so that pfn_valid() is > > true, kern_addr_valid() would return true. I don't thin that was the > > intention. > > > > > Would you expect to have a direct map for memory holes and similar (IOW, > > > !System RAM)? > > > > No, but we with the generic pfn_valid(), it may return true for mapped > > MMIO (with different attributes than the direct map). > > Ah, right. But can we actually run into that via kcore? > > kcore builds the RAM list via walk_system_ram_range(), IOW the resource > tree. And we end up calling kern_addr_valid() only on KCORE_RAM, > KCORE_VMEMMAP and KCORE_TEXT. It's probably fine but I'd rather do some check of the other call sites before attempting to move arm64 to the generic pfn_valid() again. -- Catalin
