[PATCH] arm64/efi: remove spurious WARN_ON for !4K kernels

Catalin Marinas catalin.marinas at arm.com
Wed May 25 08:31:33 PDT 2016

On Wed, May 25, 2016 at 04:11:56PM +0100, Mark Rutland wrote:
> Since commit 1fd55a9a09b0293a ("arm64/efi: Apply strict permissions to
> UEFI Runtime Services regions"), booting a !4K page kernel results in a
> boot-time splat on some systems, due to to a WARN_ONCE added in that
> commit which fires if the base address of an EFI memory descriptor is
> not aligned to the kernel page size (which might be 4K, 16K, or 64K).
> On page 38 of the UEFI 2.6 specification it is stated:
> 	If a 64KiB physical page contains any 4KiB page with any of the
> 	following types listed below, then all 4KiB pages in the 64KiB
> 	page must use identical ARM Memory Page Attributes (as described
> 	in Table 8):
> 	— EfiRuntimeServicesCode
> 	— EfiRuntimeServicesData
> 	— EfiReserved
> 	— EfiACPIMemoryNVS
> 	Mixed attribute mappings within a larger page are not allowed.
> On page 158 of the UEFI 2.6 specification, in the description of a
> memory descriptor, the PhysicalStart and VirtualStart fields are
> mandated as being 4K aligned, with NumberOfPages describing the number
> of 4K pages in the region.
> No further restriction on alignment is provided in the UEFI
> specification, neither generically nor in a rule specific to AArch64.
> So while attributes within a naturally-aligned 64K region must be
> consistent across memory descriptors, the regions described by those
> descriptors are not mandated to be 64K aligned.
> Not being able to apply strict permissions is sub-optimal, and worthy of
> some notice, but it is not helpful to erroneously suggest that firmware
> is buggy, nor is it beneficial to have a noisy backtrace at boot time.
> This patch downgrades the WARN_ONCE to a pr_warn_once, and re-words the
> message to also describe the implication of the insufficient alignment.
> Signed-off-by: Mark Rutland <mark.rutland at arm.com>
> Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org> 
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Jeremy Linton <jeremy.linton at arm.com>
> Cc: Leif Lindholm <leif.lindholm at linaro.org>
> Cc: Matt Fleming <matt at codeblueprint.co.uk>
> Cc: Will Deacon <will.deacon at arm.com>
> Cc: linux-efi at vger.kernel.org

Acked-by: Catalin Marinas <catalin.marinas at arm.com>

Not sure how this will go in (Matt or Will?).

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