On 2 September 2015 at 11:48, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote: > On 13 August 2015 at 19:29, Catalin Marinas <catalin.marinas@xxxxxxx> wrote: >> On Thu, Aug 13, 2015 at 03:45:07PM +0100, Suzuki K. Poulose wrote: >>> On 13/08/15 13:28, Steve Capper wrote: >>> >On 13 August 2015 at 12:34, Suzuki K. Poulose <suzuki.poulose@xxxxxxx> wrote: >>> >> __enable_mmu: >>> >>+ mrs x1, ID_AA64MMFR0_EL1 >>> >>+ ubfx x2, x1, #ID_AA64MMFR0_TGran_SHIFT, 4 >>> >>+ cmp x2, #ID_AA64MMFR0_TGran_ENABLED >>> >>+ b.ne __no_granule_support >>> >> ldr x5, =vectors >>> >> msr vbar_el1, x5 >>> >> msr ttbr0_el1, x25 // load TTBR0 >>> >>@@ -626,3 +643,8 @@ __enable_mmu: >>> >> isb >>> >> br x27 >>> >> ENDPROC(__enable_mmu) >>> >>+ >>> >>+__no_granule_support: >>> >>+ wfe >>> >>+ b __no_granule_support >>> >>+ENDPROC(__no_granule_support) >>> >>-- >>> >>1.7.9.5 >>> >> >>> > >>> >Is is possible to tell the user that the kernel has failed to boot due >>> >to the kernel granule being unsupported? >>> >>> We don't have anything up at this time. The "looping address" is actually a clue >>> to the (expert) user. Not sure we can do something, until we get something like DEBUG_LL(?) >> >> No. >> >>> Or we should let it continue and end in a panic(?). The current situation can boot a >>> multi-cluster system with boot cluster having the Tgran support(which doesn't make a >>> strong use case though). I will try out some options and get back to you. >> >> If the boot CPU does not support 16KB pages, in general there isn't much >> we can do since the console printing is done after we enabled the MMU. >> Even mapping the UART address requires fixmap support and the PAGE_SIZE >> is hard-coded in the kernel image. The DT is also mapped at run-time. >> >> While in theory it's possible to fall back to a 4KB page size just >> enough to load the DT and figure out the early console, I suggest we >> just live with the "looping address" clue. >> > > Couldn't we allocate some flag bits in the Image header to communicate > the page size to the bootloader? Something like this perhaps? ------------8<--------------- diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt index 7d9d3c2286b2..13a8aaa9a6e9 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 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
