Re: [PATCH 2/4] x86/platform/UV: Fix problem with bad UV4 EFI System Table causing panic

[Thomas Gleixner]

On Wed, 27 Jul 2016, Mike Travis wrote:

> Fix a problem that occurs if for some reason the UV4 EFI System Table
> is not available, the check inadvertantly can cause a panic.
> 
> Reviewed-by: Dimitri Sivanich <sivanich@xxxxxxx>
> Reviewed-by: Nathan Zimmer <nzimmer@xxxxxxx>
> Tested-by: Frank Ramsay <framsay@xxxxxxx>
> Tested-by: John Estabrook <estabrook@xxxxxxx>
> Signed-off-by: Mike Travis <travis@xxxxxxx>
> ---
>  arch/x86/platform/uv/bios_uv.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> --- linux-3.12.orig/arch/x86/platform/uv/bios_uv.c
> +++ linux-3.12/arch/x86/platform/uv/bios_uv.c
> @@ -201,11 +201,12 @@ void uv_bios_init(void)
>  	}
>  
>  	if (uv_systab->revision >= UV_SYSTAB_VERSION_UV4) {
> +		int size = uv_systab->size;
> +
>  		iounmap(uv_systab);
> -		uv_systab = ioremap(efi.uv_systab, uv_systab->size);

I think the changelog is bogus. What's happening here is a classic use after
unmap, which you avoid by this change.

> +		uv_systab = ioremap(efi.uv_systab, size);

Hmm?

	tglx