[PATCH v4] efi: implement mandatory locking for UEFI Runtime Services

[Matt Fleming]

On Mon, 04 Aug, at 06:16:00PM, Ard Biesheuvel wrote:
> According to section 7.1 of the UEFI spec, Runtime Services are not fully
> reentrant, and there are particular combinations of calls that need to be
> serialized. Use a spinlock to serialize all Runtime Services with respect
> to all others, even if this is more than strictly needed.

I think we should include something that explains how we've managed to
get away without an explicit runtime lock for so long,

  We've managed to get away without requiring a runtime services lock
  until now because most of the interactions with EFI involve EFI
  variables, and those operations are already serialised with
  __efivars->lock.

and then a little bit of blurb about why that's no longer good enough.

> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> ---
>  arch/x86/include/asm/efi.h              |   2 +
>  drivers/firmware/efi/runtime-wrappers.c | 154 +++++++++++++++++++++++++++++---
>  2 files changed, 146 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
> index 044a2fd3c5fe..b39ee5f2c02d 100644
> --- a/arch/x86/include/asm/efi.h
> +++ b/arch/x86/include/asm/efi.h
> @@ -86,6 +86,8 @@ extern void __iomem *efi_ioremap(unsigned long addr, unsigned long size,
>  
>  #endif /* CONFIG_X86_32 */
>  
> +#define efi_in_nmi()	in_nmi()
> +

Remind me why this is needed for x86 but not for arm again?

The rest looks good. I'm just running it through some tests now.

Thanks Ard.

-- 
Matt Fleming, Intel Open Source Technology Center