linux-kernel - Re: [PATCH 01/23] x86/fpu: Use ULL for shift in xfeature_uncompacted

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Date:   Thu, 8 Nov 2018 12:38:17 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...riel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 01/23] x86/fpu: Use ULL for shift in
 xfeature_uncompacted_offset()

On Wed, Nov 07, 2018 at 08:48:36PM +0100, Sebastian Andrzej Siewior wrote:
> The xfeature mask is 64bit so a shift from a number to its mask should
> have LL prefix or else nr > 31 will be lost. This is not a problem now
> but should XFEATURE_MASK_SUPERVISOR gain a bit >31 then this check won't
> catch it.
> 
> Add a ULL suffix so >31bit number will be properly shifted.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  arch/x86/kernel/fpu/xstate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index 87a57b7642d36..9dc0a2c8c2755 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -444,7 +444,7 @@ static int xfeature_uncompacted_offset(int xfeature_nr)
>  	 * format. Checking a supervisor state's uncompacted offset is
>  	 * an error.
>  	 */
> -	if (XFEATURE_MASK_SUPERVISOR & (1 << xfeature_nr)) {
> +	if (XFEATURE_MASK_SUPERVISOR & (1ULL << xfeature_nr)) {

Or simply BIT_ULL(xfeature_nr).

-- 
Regards/Gruss,
    Boris.

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