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Subject: Re: [patch V2 2/5] x86/kaiser: Simplify disabling of global pages
To: Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>
References: <20171126231403.657575796@linutronix.de>
 <20171126232414.393912629@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>, Rik van Riel <riel@redhat.com>,
        daniel.gruss@iaik.tugraz.at, hughd@google.com, keescook@google.com,
        linux-mm@kvack.org, michael.schwarz@iaik.tugraz.at,
        moritz.lipp@iaik.tugraz.at, richard.fellner@student.tugraz.at
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <0b5a64f1-9979-ae56-99f8-72c3802a9c60@linux.intel.com>
Date: Mon, 27 Nov 2017 10:15:33 -0800
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On 11/26/2017 03:14 PM, Thomas Gleixner wrote:
> +static void enable_global_pages(void)
> +{
> +#ifndef CONFIG_KAISER
> +	__supported_pte_mask |= _PAGE_GLOBAL;
> +#endif
> +}
> +
>  static void __init probe_page_size_mask(void)
>  {
>  	/*
> @@ -179,11 +186,11 @@ static void __init probe_page_size_mask(
>  		cr4_set_bits_and_update_boot(X86_CR4_PSE);
>  
>  	/* Enable PGE if available */
> +	__supported_pte_mask |= _PAGE_GLOBAL;
>  	if (boot_cpu_has(X86_FEATURE_PGE)) {
>  		cr4_set_bits_and_update_boot(X86_CR4_PGE);
> -		__supported_pte_mask |= _PAGE_GLOBAL;
> -	} else
> -		__supported_pte_mask &= ~_PAGE_GLOBAL;
> +		enable_global_pages();
> +	}

This looks a little funky.  Doesn't this or _PAGE_GLOBAL into
__supported_pte_mask twice?  Once before the if(), and then a second
time via enable_global_pages() inside the if?

Did you intend for it to be masked *out* in the first one and then or'd
back in via enable_global_pages()?