linux-kernel - Re: [patch 1/2] x86/mm/pti: Handle unaligned address gracefully in pti_clone

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Message-ID: <alpine.DEB.2.21.1908282144200.1938@nanos.tec.linutronix.de>
Date:   Wed, 28 Aug 2019 21:45:05 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ingo Molnar <mingo@...nel.org>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Song Liu <songliubraving@...com>,
        Joerg Roedel <jroedel@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [patch 1/2] x86/mm/pti: Handle unaligned address gracefully in
 pti_clone_pagetable()

On Wed, 28 Aug 2019, Ingo Molnar wrote:
> >  		pmd = pmd_offset(pud, addr);
> >  		if (pmd_none(*pmd)) {
> > -			addr += PMD_SIZE;
> > +			WARN_ON_ONCE(addr & PMD_MASK);
> > +			addr = round_up(addr + 1, PMD_SIZE);
> 
> So given that PUD_MASK and PMD_MASK are masking out the *offset*:
> 
>  arch/x86/include/asm/pgtable_64_types.h:#define PMD_MASK	(~(PMD_SIZE - 1))
> 
> Didn't we want something like:
> 
> 			WARN_ON_ONCE(addr & ~PUD_MASK);
> 
> 			WARN_ON_ONCE(addr & ~PMD_MASK);
> 
> to warn about an unaligned 'addr', or am I misreading the intent here?

Bah, right you are...