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? >> 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. > 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. 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
