linux-kernel - Re: [PATCH] x86, msr: fix rdmsrl_safe_on

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Date:   Wed, 28 Mar 2018 12:08:44 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     x86 <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] x86, msr: fix rdmsrl_safe_on_cpu()

On Tue, Mar 27, 2018 at 08:22:33PM -0700, Eric Dumazet wrote:
> When changing rdmsr_safe_on_cpu() to schedule, I missed that
> __rdmsr_safe_on_cpu() was also used by rdmsrl_safe_on_cpu()
> 
> Lets make rdmsrl_safe_on_cpu() a wrapper instead of copy/pasting
> the code I added for the completion handling.
> 
> Fixes: 07cde313b2d2 ("x86/msr: Allow rdmsr_safe_on_cpu() to schedule")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: kbuild test robot <fengguang.wu@...el.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> ---
>  arch/x86/lib/msr-smp.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/lib/msr-smp.c b/arch/x86/lib/msr-smp.c
> index 761ba062afdaf7f7d0603ed94ed6cc3e46b37f76..fee8b9c0520c9954e3cf9093332e1a9b53009b8b 100644
> --- a/arch/x86/lib/msr-smp.c
> +++ b/arch/x86/lib/msr-smp.c
> @@ -225,16 +225,13 @@ EXPORT_SYMBOL(wrmsrl_safe_on_cpu);
>  
>  int rdmsrl_safe_on_cpu(unsigned int cpu, u32 msr_no, u64 *q)
>  {
> +	u32 low, high;
>  	int err;
> -	struct msr_info rv;
>  
> -	memset(&rv, 0, sizeof(rv));
> +	err = rdmsr_safe_on_cpu(cpu, msr_no, &low, &high);
> +	*q = (u64)high << 32 | low;
>  
> -	rv.msr_no = msr_no;
> -	err = smp_call_function_single(cpu, __rdmsr_safe_on_cpu, &rv, 1);
> -	*q = rv.reg.q;
> -
> -	return err ? err : rv.err;
> +	return err;
>  }
>  EXPORT_SYMBOL(rdmsrl_safe_on_cpu);
>  
> -- 

I guess now that the rdmsr* side does this, you probably should convert
the wrmsr* side as well.

Thx.

-- 
Regards/Gruss,
    Boris.

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