On Thu, May 28, 2020 at 10:15:10AM -0500, Steve Wahl wrote: > On Thu, May 28, 2020 at 05:07:31PM +0800, Baoquan He wrote: > > On 05/26/20 at 01:49pm, David Hildenbrand wrote: > > > On 26.05.20 13:32, Mike Rapoport wrote: > > > > Hello Baoquan, > > > > > > > > I do not object to your original fix with careful check for pfn validity. > > > > > > > > But I still think that the memory reserved by the firmware is still > > > > memory and it should be added to memblock.memory. This way the memory > > > > > > If it's really memory that could be read/written, I think I agree. > > > > I would say some of them may not be allowed to be read/written, if I > > understand it correctly. I roughly went through the x86 init code, there > > are some places where mem region is marked as E820_TYPE_RESERVED so that > > they are not touched after initialization. E.g: > > > > 1) pfn 0 > > In trim_bios_range(), we set the pfn 0 as E820_TYPE_RESERVED. You can > > see the code comment, this is a BIOS owned area, but not kernel RAM. > > > > 2)GART reserved region > > In early_gart_iommu_check(), GART IOMMU firmware will reserve a region > > in an area, firmware designer won't map system RAM into that area. > > > > And also intel_graphics_stolen(), arch_rmrr_sanity_check(), these > > regions are not system RAM backed area, reading from or writting into > > these area may cause error. > > > > Futhermore, there's a KASLR bug found by HPE, its triggering and root > > cause are written into below commit log. You can see that accessing to > > firmware reserved region caused BIOS to halt system when cpu doing > > speculative. > > > > commit 2aa85f246c181b1fa89f27e8e20c5636426be624 > > Author: Steve Wahl <steve.wahl@xxxxxxx> > > Date: Tue Sep 24 16:03:55 2019 -0500 > > > > x86/boot/64: Make level2_kernel_pgt pages invalid outside kernel area > > > > Our hardware (UV aka Superdome Flex) has address ranges marked > > reserved by the BIOS. Access to these ranges is caught as an error, > > causing the BIOS to halt the system. > > Thank you for CC'ing me. Coming into the middle of the conversation, > I am trying to understand the implications of what's being discussed > here, but not being very successful at it. > > For the HPE UV hardware, the addresses listed in the reserved range > must never be accessed, or (as we discovered) even be reachable by an > active page table entry. Any active page table entry covering the > region allows the processor to issue speculative accesses to the > region, resulting in the BIOS halt mentioned. > > I'm not sure if the discussion above about adding the region to > memblock.memory would result in an active mapping of the region or > not. If it did, we'd have problems. The discussion is whether regions marked as E820_RESERVED should be considered as RAM or not. For the hardware that cannot tolerate acceses to these areas like HPE UV, it should not :) I still think that keeping them only in memblock.reserved creates more problems than it solves, but simply adding E820_RESERVED areas to memblock.memory just won't work. I'll try to come up with something better Really Soon (c). > Thanks, > > Steve Wahl, HPE -- Sincerely yours, Mike.
