linux-kernel - Re: [PATCH RFC V2 12/17] memremap: Add zone device access protection

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Message-ID: <20200717091718.GA10769@hirez.programming.kicks-ass.net>
Date:   Fri, 17 Jul 2020 11:17:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     ira.weiny@...el.com
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC V2 12/17] memremap: Add zone device access protection

On Fri, Jul 17, 2020 at 12:20:51AM -0700, ira.weiny@...el.com wrote:
> +void dev_access_disable(void)
> +{
> +	unsigned long flags;
> +
> +	if (!static_branch_unlikely(&dev_protection_static_key))
> +		return;
> +
> +	local_irq_save(flags);
> +	current->dev_page_access_ref--;
> +	if (current->dev_page_access_ref == 0)

	if (!--current->dev_page_access_ref)

> +		pks_update_protection(dev_page_pkey, PKEY_DISABLE_ACCESS);
> +	local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL_GPL(dev_access_disable);
> +
> +void dev_access_enable(void)
> +{
> +	unsigned long flags;
> +
> +	if (!static_branch_unlikely(&dev_protection_static_key))
> +		return;
> +
> +	local_irq_save(flags);
> +	/* 0 clears the PKEY_DISABLE_ACCESS bit, allowing access */
> +	if (current->dev_page_access_ref == 0)
> +		pks_update_protection(dev_page_pkey, 0);
> +	current->dev_page_access_ref++;

	if (!current->dev_page_access_ref++)

> +	local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL_GPL(dev_access_enable);


Also, you probably want something like:

static __always_inline devm_access_disable(void)
{
	if (static_branch_unlikely(&dev_protection_static_key))
		__devm_access_disable();
}

static __always_inline devm_access_enable(void)
{
	if (static_branch_unlikely(&dev_protection_static_key))
		__devm_access_enable();
}