linux-kernel - Re: [PATCH 12/14] arm64: Check for selected granule support

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Message-ID: <CAPvkgC3=S1BxdzZM4uUOmyXLjii48SMpCof6i6HdNeTG_fydfg@mail.gmail.com>
Date:	Thu, 13 Aug 2015 13:28:28 +0100
From:	Steve Capper <steve.capper@...aro.org>
To:	"Suzuki K. Poulose" <suzuki.poulose@....com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, kvm@...r.kernel.org,
	Marc Zyngier <marc.zyngier@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH 12/14] arm64: Check for selected granule support

On 13 August 2015 at 12:34, Suzuki K. Poulose <suzuki.poulose@....com> wrote:
> From: "Suzuki K. Poulose" <suzuki.poulose@....com>
>
> Ensure that the selected page size is supported by the
> CPU(s).
>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Signed-off-by: Suzuki K. Poulose <suzuki.poulose@....com>
> ---
>  arch/arm64/include/asm/sysreg.h |    6 ++++++
>  arch/arm64/kernel/head.S        |   24 +++++++++++++++++++++++-
>  2 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index a7f3d4b..e01d323 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -87,4 +87,10 @@ static inline void config_sctlr_el1(u32 clear, u32 set)
>  }
>  #endif
>
> +#define ID_AA64MMFR0_TGran4_SHIFT      28
> +#define ID_AA64MMFR0_TGran64_SHIFT     24
> +
> +#define ID_AA64MMFR0_TGran4_ENABLED    0x0
> +#define ID_AA64MMFR0_TGran64_ENABLED   0x0
> +
>  #endif /* __ASM_SYSREG_H */
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 01b8e58..0cb04db 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -31,10 +31,11 @@
>  #include <asm/cputype.h>
>  #include <asm/kernel-pgtable.h>
>  #include <asm/memory.h>
> -#include <asm/thread_info.h>
>  #include <asm/pgtable-hwdef.h>
>  #include <asm/pgtable.h>
>  #include <asm/page.h>
> +#include <asm/sysreg.h>
> +#include <asm/thread_info.h>
>  #include <asm/virt.h>
>
>  #define __PHYS_OFFSET  (KERNEL_START - TEXT_OFFSET)
> @@ -606,9 +607,25 @@ ENDPROC(__secondary_switched)
>   *  x27 = *virtual* address to jump to upon completion
>   *
>   * other registers depend on the function called upon completion
> + * Checks if the selected granule size is supported by the CPU.
>   */
> +#if    defined(CONFIG_ARM64_64K_PAGES)
> +
> +#define ID_AA64MMFR0_TGran_SHIFT       ID_AA64MMFR0_TGran64_SHIFT
> +#define ID_AA64MMFR0_TGran_ENABLED     ID_AA64MMFR0_TGran64_ENABLED
> +
> +#else
> +
> +#define ID_AA64MMFR0_TGran_SHIFT       ID_AA64MMFR0_TGran4_SHIFT
> +#define ID_AA64MMFR0_TGran_ENABLED     ID_AA64MMFR0_TGran4_ENABLED
> +
> +#endif
>         .section        ".idmap.text", "ax"
>  __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
>

Hi Suzuki,
Is is possible to tell the user that the kernel has failed to boot due
to the kernel granule being unsupported?

Cheers,
--
Steve
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