linux-kernel - Re: [PATCHv3 08/11] arm64: Check for selected granule support

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Date:	Thu, 15 Oct 2015 11:45:15 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Jeremy Linton <jeremy.linton@....com>
Cc:	"Suzuki K. Poulose" <suzuki.poulose@....com>,
	linux-arm-kernel@...ts.infradead.org, steve.capper@...aro.org,
	ard.biesheuvel@...aro.org, marc.zyngier@....com,
	catalin.marinas@....com, will.deacon@....com,
	linux-kernel@...r.kernel.org, christoffer.dall@...aro.org
Subject: Re: [PATCHv3 08/11] arm64: Check for selected granule support

On Wed, Oct 14, 2015 at 04:13:47PM -0500, Jeremy Linton wrote:
> On 10/14/2015 06:20 AM, Suzuki K. Poulose wrote:
> 
> >+ * Checks if the selected granule size is supported by the CPU.
> >+ * If it doesn't park the CPU
> 
> The problem is when you park the boot CPU.
> 
> I think for EFI there is a slightly better error mechanism. This
> tweak will print an error and return to the EFI boot manager rather
> than hanging the machine without any notification. Now it prints:
> 
> EFI stub: Booting Linux Kernel...
> EFI stub: ERROR: 16K granule not supported by this machine
> EFI stub: ERROR: Failed to relocate kernel
> FS4:\>

Neat. We should definitely have checks like this in the stub.

However, we still need checks in head.S, given !EFI systems, SMP, and
kexec, so this is a complementary mechanism.

Thanks,
Mark.

> Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> ---
>  arch/arm64/kernel/efi-stub.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/arch/arm64/kernel/efi-stub.c b/arch/arm64/kernel/efi-stub.c
> index 816120e..90fb868 100644
> --- a/arch/arm64/kernel/efi-stub.c
> +++ b/arch/arm64/kernel/efi-stub.c
> @@ -25,6 +25,20 @@ efi_status_t __init
> handle_kernel_image(efi_system_table_t *sys_table_arg,
>         unsigned long kernel_size, kernel_memsize = 0;
>         unsigned long nr_pages;
>         void *old_image_addr = (void *)*image_addr;
> +       u32 aa64mmfr0_el1;
> +
> +#ifdef CONFIG_ARM64_16K_PAGES
> +       /*
> +        * check to see if this kernel image is
> +        * compatible with the current system
> +        */
> +       asm volatile("mrs %0, ID_AA64MMFR0_EL1" : "=r" (aa64mmfr0_el1));
> +       aa64mmfr0_el1 >>= ID_AA64MMFR0_TGRAN16_SHIFT;
> +       if ((aa64mmfr0_el1 & ID_AA64MMFR0_TGRAN4_ON) == 0) {
> +               pr_efi_err(sys_table_arg, "16K granule not supported
> by this machine\n");
> +               return EFI_UNSUPPORTED;
> +       }
> +#endif
> 
>         /* Relocate the image, if required. */
>         kernel_size = _edata - _text;
> -- 
> 2.4.3
> 
> 
> 
> 
> 
> 
> 
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