Re: [PATCH] efi/arm64: don't apply MEMBLOCK_NOMAP to UEFI memory map mapping

[Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>]

On Wed, Mar 30, 2016 at 09:46:23AM +0200, Ard Biesheuvel wrote:
> Hi Matt,
> 
> Could we queue this as a fix for v4.6 with a cc:stable for v4.5, please?
> (assuming no objections from any of the cc'ees)

FWIW:

Acked-by: Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>

Yes, this is a temporary hack, but it's small, fixes a real issue and
you're already working on a proper solution anyway.

Will

> ----------8<--------------
> Commit 4dffbfc48d65 ("arm64/efi: mark UEFI reserved regions as
> MEMBLOCK_NOMAP") updated the mapping logic of both the RuntimeServices
> regions as well as the kernel's copy of the UEFI memory map to set the
> MEMBLOCK_NOMAP flag, which causes these regions to be omitted from the
> kernel direct mapping, and from being covered by a struct page.
> For the RuntimeServices regions, this is an obvious win, since the contents
> of these regions have significance to the firmware executable code itself,
> and are mapped in the EFI page tables using attributes that are described in
> the UEFI memory map, and which may differ from the attributes we use for
> mapping system RAM. It also prevents the contents from being modified
> inadvertently, since the EFI page tables are only live during runtime
> service invocations.
> 
> None of these concerns apply to the allocation that covers the UEFI memory
> map, since it is entirely owned by the kernel. Setting the MEMBLOCK_NOMAP on
> the region did allow us to use ioremap_cache() to map it both on arm64 and
> on ARM, since the latter does not allow ioremap_cache() to be used on
> regions that are covered by a struct page.
> 
> The ioremap_cache() on ARM restriction will be lifted in the v4.7 timeframe,
> but in the mean time, it has been reported that commit 4dffbfc48d65 causes
> a regression on 64k granule kernels. This is due to the fact that, given
> the 64 KB page size, the region that we end up removing from the kernel
> direct mapping is rounded up to 64 KB, and this 64 KB page frame may be
> shared with the initrd when booting via GRUB (which does not align its
> EFI_LOADER_DATA allocations to 64 KB like the stub does). This will crash
> the kernel as soon as it tries to access the initrd.
> 
> Since the issue is specific to arm64, revert back to memblock_reserve()'ing
> the UEFI memory map when running on arm64. This is a temporary fix for v4.5
> and v4.6, and will be superseded in the v4.7 timeframe when we will be able
> to move back to memblock_reserve() unconditionally.
> 
> Fixes: 4dffbfc48d65 ("arm64/efi: mark UEFI reserved regions as MEMBLOCK_NOMAP")
> Reported-by: Mark Salter <msalter-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
>  drivers/firmware/efi/arm-init.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/firmware/efi/arm-init.c b/drivers/firmware/efi/arm-init.c
> index aa1f743152a2..8714f8c271ba 100644
> --- a/drivers/firmware/efi/arm-init.c
> +++ b/drivers/firmware/efi/arm-init.c
> @@ -203,7 +203,19 @@ 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)));
> +
> +	if (IS_ENABLED(CONFIG_ARM)) {
> +		/*
> +		 * ARM currently does not allow ioremap_cache() to be called on
> +		 * memory regions that are covered by struct page. So remove the
> +		 * UEFI memory map from the linear mapping.
> +		 */
> +		memblock_mark_nomap(params.mmap & PAGE_MASK,
> +				    PAGE_ALIGN(params.mmap_size +
> +					       (params.mmap & ~PAGE_MASK)));
> +	} else {
> +		memblock_reserve(params.mmap & PAGE_MASK,
> +				 PAGE_ALIGN(params.mmap_size +
> +					    (params.mmap & ~PAGE_MASK)));
> +	}
>  }
> -- 
> 2.5.0
> 
> 
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