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Subject: Re: [PATCH v2 1/2] x86/boot/64: Make level2_kernel_pgt pages invalid
 outside kernel area.
To:     Steve Wahl <steve.wahl@hpe.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Juergen Gross <jgross@suse.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Jordan Borgner <mail@jordan-borgner.de>,
        Feng Tang <feng.tang@intel.com>, linux-kernel@vger.kernel.org,
        Chao Fan <fanc.fnst@cn.fujitsu.com>,
        Zhenzhong Duan <zhenzhong.duan@oracle.com>,
        Baoquan He <bhe@redhat.com>, russ.anderson@hpe.com,
        dimitri.sivanich@hpe.com, mike.travis@hpe.com
References: <cover.1569004922.git.steve.wahl@hpe.com>
 <51b87d62e0cade3c46a69706b9be249190abc7bd.1569004923.git.steve.wahl@hpe.com>
 <63a38733-974f-9032-1980-9a8289d72d21@intel.com>
 <20190924200440.GC8138@swahl-linux>
From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <e4692a3e-40da-c504-d1a1-b7231a5673ca@intel.com>
Date:   Tue, 24 Sep 2019 13:15:07 -0700
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On 9/24/19 1:04 PM, Steve Wahl wrote:
> Given that, would you feel better with A) the way I have it, B) your
> rewrite, or C) with an inline comment for each part of the loop:
> 
> 	pmd = fixup_pointer(level2_kernel_pgt, physaddr);
> 
> 	/* invalidate pages before the kernel image */
> 	for (i = 0; i < pmd_index((unsigned long)_text); i++)
> 		pmd[i] &= ~_PAGE_PRESENT;
> 
> 	/* fixup pages that are part of the kernel image */
> 	for (; i <= pmd_index((unsigned long)_end); i++)
> 		if (pmd[i] & _PAGE_PRESENT)
> 			pmd[i] += load_delta;
> 
> 	/* invalidate pages after the kernel image */
> 	for (; i < PTRS_PER_PMD; i++)
> 		pmd[i] &= ~_PAGE_PRESENT;

I don't feel super strongly either way, but I'd prefer doing B or C over
nothing.