linux-kernel - Re: [PATCH] x86/cpu: Fix SMAP check in PVOPS environments

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Date:	Fri, 5 Jun 2015 09:13:20 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Xen-devel <xen-devel@...ts.xen.org>,
	David Vrabel <david.vrabel@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	lguest@...ts.ozlabs.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86/cpu: Fix SMAP check in PVOPS environments


* Rusty Russell <rusty@...tcorp.com.au> wrote:

> As the comment in arch/x86/include/asm/paravirt_types.h says:
> 
> 	 * Get/set interrupt state.  save_fl and restore_fl are only
> 	 * expected to use X86_EFLAGS_IF; all other bits
> 	 * returned from save_fl are undefined, and may be ignored by
> 	 * restore_fl.

There should be no 'may' about this: under CONFIG_PARAVIRT_DEBUG=y the reminder of 
the flags should be cleared (or all bits should be set: that will instantly crash 
if restored verbatim), so that we trip up generic code that relies on non-IF 
restoration?

Thanks,

	Ingo
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