On Fri, 2016-01-29 at 17:16 +0100, Ard Biesheuvel wrote: > On 29 January 2016 at 16:53, Mark Salter <msalter@xxxxxxxxxx> wrote: > > On Fri, 2016-01-29 at 15:06 +0100, Ard Biesheuvel wrote: > > > On 29 January 2016 at 15:00, Mark Salter <msalter@xxxxxxxxxx> wrote: > > > > Hi Ard, > > > > > > > > I ran into an issue with your MEMBLOCK_NOMAP changes on a particular > > > > firmware. The symptom is the kernel panics at boot time when it hits > > > > an unmapped page while unpacking the initramfs. As it turns out, the > > > > start of the initramfs shares a 64k kernel page with the UEFI memmap. > > > > I can avoid the problem with: > > > > > > > > @@ -203,7 +203,7 @@ void __init efi_init(void) > > > > > > > > reserve_regions(); > > > > early_memunmap(memmap.map, params.mmap_size); > > > > - memblock_mark_nomap(params.mmap & PAGE_MASK, > > > > - PAGE_ALIGN(params.mmap_size + > > > > - (params.mmap & ~PAGE_MASK))); > > > > + memblock_reserve(params.mmap & PAGE_MASK, > > > > + PAGE_ALIGN(params.mmap_size + > > > > + (params.mmap & ~PAGE_MASK))); > > > > } > > > > > > > > > > > > But it makes me worry about the same potential problem with > > > > other reserved regions which we nomap. What do you think? > > > > > > > > > > So I take it this initramfs allocation is not made by the stub but by > > > GRUB? Since the stub rounds all allocations to 64 KB ... > > > > > Yes. GRUB. > > > > We have already fixed EDK2 a while ago to round up all regions > returned by AllocatePages() to round up to 64 KB. Do you know if this > is a GRUB issue (i.e., it traverses the memory map and finds a free > range and explicitly allocates it) or a firmware issue? Grub uses AllocatePages() to get memory for the initrd. The firmware that hit this was fairly old (released last May I think). The problem didn't show up on newer firmware for same platform but that doesn't really mean anything definitive. > > > > In any case, regardless of the underlying cause, if any part of the > > > initramfs turns out not to be covered by the linear mapping, we should > > > invoke your code to move it. So I think it should be a matter of > > > refining the logic in relocate_initrd() to do the right thing in this > > > case > > > > That thought had crossed my mind. I think it would be easy enough to > > trigger the copy if first or last page of initrd is unmapped. > > Indeed. If some page in the middle is missing, then you're really > doing something fishy, so I don't see why we should care about that as > well. > > > Somewhat > > related to this is that I want to rework this old patch to deal with > > acpi tables outside mapped ram: > > > > https://lkml.org/lkml/2015/5/14/357 > > > > Basically, we should be able to just do: > > > > diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h > > index 15e0aad..4ea638c 100644 > > --- a/arch/arm64/include/asm/acpi.h > > +++ b/arch/arm64/include/asm/acpi.h > > @@ -32,7 +32,7 @@ > > static inline void __iomem *acpi_os_ioremap(acpi_physical_address phys, > > acpi_size size) > > { > > - if (!page_is_ram(phys >> PAGE_SHIFT)) > > + if (!memblock_is_memory(phys)) > > return ioremap(phys, size); > > > > return ioremap_cache(phys, size); > > > > I think we should fix acpi_os_ioremap(). IIRC it is used via two > different code paths that distinguish between memory and I/O, and end > up using the same function for no good reason. I remember this being mentioned before. It would be a nice solution. > > > But this doesn't currently work wrt mem= which works by removing > > the end range of memblocks. If I have mem= use the nomap flag > > rather than removing the range, the above acpi_os_ioremap change > > works, but other issues crop up due to memblock_end_of_DRAM() > > returning end of all DRAM regardless of mem=. So we end up with > > PFNs and struct pages for memory which will never be in linear > > map. Fixing memblock_end_of_DRAM() to look at the flags and > > return end of mapped DRAM gets things working but I wonder about > > other potential trouble spots with this approach. Any thoughts? > > > > Actually, I think mem= should be considered a development feature, not > a production feature, and if its use is suboptimal in this respect, so > be it. It is mostly a devel/debug feature but the production case is with kdump where the kexec'd kernel gathering the dump info has to be restricted to its own sandbox. > > But to address this particular issue, it would probably be better to > fix page_is_ram(). I have made some attempts in that direction in the > past, but that never landed anywhere. Since ACPI on arm64 is tightly > coupled to UEFI, implementing page_is_ram() as something that > interrogates the UEFI memory map if efi_enabled(EFI_MEMMAP) would be > reasonable imo. (Or perhaps putting that in acpi_os_ioremap() > directly?) > > > > > > > > > Your suggested change will break 32-bit ARM, since we use > > > ioremap_nocache() to map the UEFI memory map, and ARM does not allow > > > that on ranges that are part of the linear mapping. > > > > okay. I'll put together a patch to the initrd relocating code. > > > > Great! -- 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
