On 9 August 2018 at 11:13, Dave Young <dyoung@xxxxxxxxxx> wrote: > On 08/09/18 at 09:33am, Mike Galbraith wrote: >> On Thu, 2018-08-09 at 12:21 +0800, Dave Young wrote: >> > Hi Mike, >> > >> > Thanks for the patch! >> > On 08/08/18 at 04:03pm, Mike Galbraith wrote: >> > > When booting with efi=noruntime, we call efi_runtime_map_copy() while >> > > loading the kdump kernel, and trip over a NULL efi.memmap.map. Avoid >> > > that and a useless allocation when the only mapping we can use (1:1) >> > > is not available. >> > >> > At first glance, efi_get_runtime_map_size should return 0 in case >> > noruntime. >> >> What efi does internally at unmap time is to leave everything except >> efi.mmap.map untouched, setting it to NULL and turning off EFI_MEMMAP, >> rendering efi.mmap.map accessors useless/unsafe without first checking >> EFI_MEMMAP. > > Probably the x86 efi_init should reset nr_map to zero in case runtime is > disabled. But let's see how Ard thinks about this and cc linux-efi. > > As for efi_get_runtime_map_size, it was introduced for x86 kexec use. > for copying runtime maps, so I think it is reasonable this function > return zero in case no runtime. > I don't see the patch in the context so I cannot comment in great detail. In any case, it is better to decouple EFI_MEMMAP from EFI_RUNTIME dependencies. On x86, one may imply the other, but this is not generally the case. That means that efi_get_runtime_map_size() should probably check the EFI_RUNTIME flag, and return 0 if it is cleared. Perhaps there are other places where EFI_MEMMAP flag checks are missing, but I consider that a separate issue.
