Hi Akashi, On 26/04/18 08:40, AKASHI Takahiro wrote: > On Wed, Apr 25, 2018 at 02:22:07PM +0100, James Morse wrote: >> On 25/04/18 10:20, AKASHI Takahiro wrote: >>> On Tue, Apr 24, 2018 at 05:08:57PM +0100, James Morse wrote: >>>> If we squash the memblock_reserved() stuff down so it appears as a top level >>>> 'reserved' region too, I don't think we do. >>> >>> If I correctly understand, you're talking about my format (E). >>> As I said, it will fix the issue without modifying user-space, but >>> >>> || This does not only look quite noisy but also ignores the fact that >>> || reserved regions are part of System RAM (or memblock.memory). >> >> I agree its noisy, there are significantly more 'reserved' areas, but these are >> all either nomap or memblock_reserved(). >> >> Why does it matter if a reserved-region is nomap or memblock_reserved()? Any new >> kernel will learn the difference from the EFI memory map and make its own decisions. > > Yeah, kernel can do (though kernel won't look though system resources list > for this purpose anyway), what about kexec-like user applications? > It may want to seek /proc/iomem to identify all the *usable* memory on > the system, that is "System RAM", but doesn't care whether some range is > reserved or not (for some reason) yet does care !NOMAP. Do you have an example application? This would have to be a program digging in /dev/mem where it wants to touch memory the kernel has reserved, but doesn't want to receive a signal if it touches memory that's nomap. This doesn't seem a likely use-case. We could change the names for the memblock_reserved()/nomap entries, but as kexec-tools spots 'reserved' and almost does the right thing, I kept it as it is. >>>> This prevents the efi-memory-map >>>> being overwritten on kernels since kexec was merged. >>>> >>>> Its horribly fiddly to do this. The kernel code/data are special reserved >>>> regions that we already describe as a subset of system-ram, even though they are >>>> both also fragments of a bigger memblock_reserved() block. >>> >>> Actually, we don't have to avoid kernel code/data regions as copying >>> loaded data to the final destinations will be done at the very end of kexec. >> >> For kexec yes, but that is the existing format of the file, which we shouldn't >> change, otherwise we break something else. > > One trivial downside in this approach is that a secondary kernel will be > loaded at an address different from the one of current kernel. > While it is sane, it looks a bit odd that, every time kexec'ed, a new> kernel (code/data) is located back and forth :) Yes, but all versions of the kernel that support kexec will be quite happy with this. The memory below the kernel could be re-used since KASLR support was merged before kexec. I was more worried that the extra fragmentation would cause kexec-tools to stop searching early, as it seems to have a #defined'd limit of how much of that file it will parse. But, this would be an existing bug, because there could be many nomap regions up-front before any large-enough chunk of system-ram appears. Thanks, James -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
