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Date: Thu, 4 Sep 2014 18:03:49 +0100
From: Will Deacon <will.deacon@arm.com>
To: Kees Cook <keescook@chromium.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Rabin Vincent <rabin@rab.in>, Laura Abbott <lauraa@codeaurora.org>,
        Rob Herring <robh@kernel.org>,
        Leif Lindholm <leif.lindholm@linaro.org>,
        "msalter@redhat.com" <msalter@redhat.com>,
        Liu hua <sdu.liu@huawei.com>,
        Nikolay Borisov <Nikolay.Borisov@arm.com>,
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        Doug Anderson <dianders@google.com>,
        Jason Wessel <jason.wessel@windriver.com>,
        Catalin Marinas <Catalin.Marinas@arm.com>,
        Russell King - ARM Linux <linux@arm.linux.org.uk>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v5 3/8] arm: fixmap: implement __set_fixmap()
Message-ID: <20140904170349.GL7156@arm.com>
References: <1409781429-27593-1-git-send-email-keescook@chromium.org>
 <1409781429-27593-4-git-send-email-keescook@chromium.org>
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Hi Kees,

On Wed, Sep 03, 2014 at 10:57:04PM +0100, Kees Cook wrote:
> This is used from set_fixmap() and clear_fixmap() via asm-generic/fixmap.h.
> Also makes sure that the fixmap allocation fits into the expected range.
> 
> Based on patch by Rabin Vincent.

[...]

> +void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
> +{
> +	unsigned long vaddr = __fix_to_virt(idx);
> +	pte_t *pte = pte_offset_kernel(pmd_off_k(vaddr), vaddr);
> +
> +	/* Make sure fixmap region does not exceed available allocation. */
> +	BUILD_BUG_ON(FIXADDR_START + (__end_of_fixed_addresses * PAGE_SIZE) >
> +		     FIXADDR_END);
> +	BUG_ON(idx >= __end_of_fixed_addresses);
> +
> +	if (pgprot_val(prot))
> +		set_pte_at(NULL, vaddr, pte,
> +			pfn_pte(phys >> PAGE_SHIFT, prot));
> +	else
> +		pte_clear(NULL, vaddr, pte);
> +
> +	/*
> +	 * Given the potential a15 tlbi errata, we can only do tlb flushes
> +	 * with interrupts disabled. Callers must have taken care of this.
> +	 */
> +	WARN_ON_ONCE(!irqs_disabled());
> +	flush_tlb_kernel_range(vaddr, vaddr + PAGE_SIZE);

Aha, this explains why we were confusing each other! The issue is that
interrupts must be *enabled*, so this code does the exact opposite of
what we need.

I think this got lost in a sea of double negatives during the last round
of review.

Will