On Sun, 20 Sep 2020 at 01:49, Nicolas Pitre <nico@xxxxxxxxxxx> wrote: > > On Fri, 18 Sep 2020, Ard Biesheuvel wrote: > > > This series is inspired by Zhei Len's series [0], which updates the > > ARM p2v patching code to optionally support p2v relative alignments > > of as little as 64 KiB. > > > > Reducing this alignment is necessary for some specific Huawei boards, > > but given that reducing this minimum alignment will make the boot > > sequence more robust for all platforms, especially EFI boot, which > > no longer relies on the 128 MB masking of the decompressor load address, > > but uses firmware memory allocation routines to find a suitable spot > > for the decompressed kernel. > > > > This series is not based on Zhei Len's code, but addresses the same > > problem, and takes some feedback given in the review into account: > > - use of a MOVW instruction to avoid two adds/adcs sequences when dealing > > with the carry on LPAE > > - add support for Thumb2 kernels as well > > - make the change unconditional - it will bit rot otherwise, and has value > > for other platforms as well. > > > > The first four patches are general cleanup and preparatory changes. > > Patch #5 implements the switch to a MOVW instruction without changing > > the minimum alignment. > > Patch #6 reduces the minimum alignment to 2 MiB. > > > > Tested on QEMU in ARM/!LPAE, ARM/LPAE, Thumb2/!LPAE and Thumb2/LPAE modes. > > At this point I think this really ought to be split into a file of its > own... and maybe even rewritten in C. Even though I wrote the original > code, I no longer understand it without re-investing time into it. But > in either cases the whole of head.S would need to have its registers > shuffled first to move long lived values away from r0-r3,ip,lr to allow > for standard function calls. > I agree with that in principle, however, running C code with a stack with the MMU off is slightly risky. I have managed to simplify the code a bit more (given that some patching was not needed to begin with), and I can add some more comments to head.S to annotate the actions.
