linux-kernel - Re: [PATCH v2 3/5] generic/pgtable: Introduce set_pte

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Message-ID: <4bc8cab6-4e1a-c3b9-0023-3ecde932cc70@intel.com>
Date:   Mon, 3 Dec 2018 09:53:00 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Dan Williams <dan.j.williams@...el.com>, tglx@...utronix.de
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/5] generic/pgtable: Introduce set_pte_safe()

On 11/30/18 4:35 PM, Dan Williams wrote:
> +/*
> + * The _safe versions of set_{pte,pmd,pud,p4d,pgd} validate that the
> + * entry was not populated previously. I.e. for cases where a flush-tlb
> + * is elided, double-check that there is no stale mapping to shoot down.
> + */

Functionally these look great to me.

The only thing I'd suggest is to make the comment more about when to use
these, instead of what they do:

	Use the set_p*_safe() version when confident that *no*
	TLB flush will be required as a result of the "set", such
	as setting non-present entries or when possibly superfluously
	re-setting an entry.