Re: [stable-3.4] possibly revert "KVM: X86 emulator: fix source operand decoding..."

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Il 04/09/2013 18:44, Paul Gortmaker ha scritto:
> Hi Greg,
> 
> The 3.4.44+ cherry pick:
> 
>   ----------------
>   commit 5b5b30580218eae22609989546bac6e44d0eda6e
>   Author: Gleb Natapov <gleb@xxxxxxxxxx>
>   Date:   Wed Apr 24 13:38:36 2013 +0300
> 
>     KVM: X86 emulator: fix source operand decoding for 8bit mov[zs]x instructions
>     
>     commit 660696d1d16a71e15549ce1bf74953be1592bcd3 upstream.
>     
>     Source operand for one byte mov[zs]x is decoded incorrectly if it is in
>     high byte register. Fix that.
>     
>     Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
>     Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>   ----------------
> 
> introduces the following:
> 
> arch/x86/kvm/emulate.c: In function ‘decode_operand’:
> arch/x86/kvm/emulate.c:3974:4: warning: passing argument 1 of ‘decode_register’ makes integer from pointer without a cast [enabled by default]
> arch/x86/kvm/emulate.c:789:14: note: expected ‘u8’ but argument is of type ‘struct x86_emulate_ctxt *’
> arch/x86/kvm/emulate.c:3974:4: warning: passing argument 2 of ‘decode_register’ makes pointer from integer without a cast [enabled by default]
> arch/x86/kvm/emulate.c:789:14: note: expected ‘long unsigned int *’ but argument is of type ‘u8’
> 
> Based on the severity of the warnings above, I'm reasonably sure there will
> be some kind of runtime regressions due to this, but I stopped to investigate
> the warnings as soon as I saw them, before any run time testing.
> 
> It happens because mainline v3.7-rc1~113^2~40 (dd856efafe60) does this:
> 
> -static void *decode_register(u8 modrm_reg, unsigned long *regs,
> +static void *decode_register(struct x86_emulate_ctxt *ctxt, u8 modrm_reg,
> 
> Since 660696d1d16a71e1 was only applied to stable 3.4, 3.8, and 3.9 -- and
> the prerequisite above is in 3.7+, the issue should be limited to 3.4.44+

Right, the fix is not important to have for 3.4 kernels.

Paolo

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