Re: [Xen-devel] [PATCH v2 1/3] x86/hvm: Don't raise #GP behind the emulators back for MSR accesses

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 02/20/2017 05:28 AM, Andrew Cooper wrote:
> The current hvm_msr_{read,write}_intercept() infrastructure calls
> hvm_inject_hw_exception() directly to latch a fault, and returns
> X86EMUL_EXCEPTION to its caller.
>
> This behaviour is problematic for the hvmemul_{read,write}_msr() paths, as the
> fault is raised behind the back of the x86 emulator.
>
> Alter the behaviour so hvm_msr_{read,write}_intercept() simply returns
> X86EMUL_EXCEPTION, leaving the callers to actually inject the #GP fault.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>


>  
> diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
> index 894c457..b864535 100644
> --- a/xen/arch/x86/hvm/svm/svm.c
> +++ b/xen/arch/x86/hvm/svm/svm.c
> @@ -1744,7 +1744,6 @@ static int svm_msr_read_intercept(unsigned int msr, 
> uint64_t *msr_content)
>      return X86EMUL_OKAY;
>  
>   gpf:
> -    hvm_inject_hw_exception(TRAP_gp_fault, 0);
>      return X86EMUL_EXCEPTION;
>  }
>  
> @@ -1897,7 +1896,6 @@ static int svm_msr_write_intercept(unsigned int msr, 
> uint64_t msr_content)
>      return result;
>  
>   gpf:
> -    hvm_inject_hw_exception(TRAP_gp_fault, 0);
>      return X86EMUL_EXCEPTION;
>  }

The label can be dropped with a direct return instead of a 'goto'.
Either way

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>


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