From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Thu, 17 Sep 2015 11:17:04 +0100 Subject: [PATCH] arm64: expose kernel page size in Image header flags In-Reply-To: <1442482345-7679-1-git-send-email-ard.biesheuvel@linaro.org> References: <1442482345-7679-1-git-send-email-ard.biesheuvel@linaro.org> Message-ID: <20150917101704.GA12808@leverpostej> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Sep 17, 2015 at 10:32:25AM +0100, Ard Biesheuvel wrote: > In order for a bootloader to be able to decide whether a certain > arm64 kernel image is compatible with the hardware it is running > on, it needs to be able to find out for which page size the kernel > was built. This is necessary, since the architecture does not > mandate support for all page sizes it defines, and the kernel cannot > boot to a state where it can print a diagnostic if it was built for > a page size that is not supported by the hardware. > > So assign two bits in the flags field of the Image header, and set > them according to the build time page size. For backward compatibility, > retain the 0b00 value as 'unspecified'. > > Acked-by: Catalin Marinas > Signed-off-by: Ard Biesheuvel This looks sane to me. FWIW: Acked-by: Mark Rutland Thanks, Mark. > --- > Documentation/arm64/booting.txt | 3 ++- > arch/arm64/kernel/image.h | 4 +++- > 2 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt > index 1690350f16e7..46056e7d766e 100644 > --- a/Documentation/arm64/booting.txt > +++ b/Documentation/arm64/booting.txt > @@ -104,7 +104,8 @@ Header notes: > - The flags field (introduced in v3.17) is a little-endian 64-bit field > composed as follows: > Bit 0: Kernel endianness. 1 if BE, 0 if LE. > - Bits 1-63: Reserved. > + Bits 1-2: Kernel page size. 0=unspecified, 1=4K, 2=16K, 3=64K > + Bits 3-63: Reserved. > > - When image_size is zero, a bootloader should attempt to keep as much > memory as possible free for use by the kernel immediately after the > diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h > index 8fae0756e175..5def289bda84 100644 > --- a/arch/arm64/kernel/image.h > +++ b/arch/arm64/kernel/image.h > @@ -47,7 +47,9 @@ > #define __HEAD_FLAG_BE 0 > #endif > > -#define __HEAD_FLAGS (__HEAD_FLAG_BE << 0) > +#define __HEAD_FLAG_PAGE_SIZE ((PAGE_SHIFT - 10) / 2) > + > +#define __HEAD_FLAGS (__HEAD_FLAG_BE << 0) | (__HEAD_FLAG_PAGE_SIZE << 1) > > /* > * These will output as part of the Image header, which should be little-endian > -- > 1.9.1 >