linux-kernel - Re: [PATCH] x86, efi: Only print warning when desc

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Date:	Wed, 27 Apr 2011 12:39:35 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Huang Ying <ying.huang@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, efi: Only print warning when desc_size is smaller
 than defined one.

On Tue, 26 Apr 2011 15:42:24 -0700
Yinghai Lu <yinghai@...nel.org> wrote:

> 
> One system get warning:
> 	Kernel-defined memdesc doesn't match the one from EFI!
> 
> UEFI spec allows GetMemoryMap() return bigger desc_size and desc_ver for future
> extension.
> And desc_size is already used to get offset of next memory entry.
> 
> Only need to check if desc_size is smaller than defined struct.
> 
> Also print the size in warning if it happens.
> 
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> 
> ---
>  arch/x86/platform/efi/efi.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/arch/x86/platform/efi/efi.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/platform/efi/efi.c
> +++ linux-2.6/arch/x86/platform/efi/efi.c
> @@ -448,9 +448,10 @@ void __init efi_init(void)
>  		printk(KERN_ERR "Could not map the EFI memory map!\n");
>  	memmap.map_end = memmap.map + (memmap.nr_map * memmap.desc_size);
>  
> -	if (memmap.desc_size != sizeof(efi_memory_desc_t))
> +	if (memmap.desc_size < sizeof(efi_memory_desc_t))
>  		printk(KERN_WARNING
> -		  "Kernel-defined memdesc doesn't match the one from EFI!\n");
> +		  "Kernel-defined memdesc size is bigger than the one from EFI! %ld > %ld\n",
> +			 sizeof(efi_memory_desc_t), memmap.desc_size);

Does it make sense for this to just be a warning? If
sizeof(efi_memory_desec_t) > sizeof(memmap.desc_size) aren't we going
to run into some pretty serious problems when we start accessing
memory descriptors?

Would it not make more sense for this to be a BUG_ON()? In the unlikely
event that the kernel's efi_memory_desc_t is too large I really don't
see how we can recover from that.

-- 
Matt Fleming, Intel Open Source Technology Center
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