linux-kernel - Re: [PATCH v2 1/2] x86/boot/64: Make level2_kernel

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Date:   Tue, 24 Sep 2019 13:15:07 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Steve Wahl <steve.wahl@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Juergen Gross <jgross@...e.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Brijesh Singh <brijesh.singh@....com>,
        Jordan Borgner <mail@...dan-borgner.de>,
        Feng Tang <feng.tang@...el.com>, linux-kernel@...r.kernel.org,
        Chao Fan <fanc.fnst@...fujitsu.com>,
        Zhenzhong Duan <zhenzhong.duan@...cle.com>,
        Baoquan He <bhe@...hat.com>, russ.anderson@....com,
        dimitri.sivanich@....com, mike.travis@....com
Subject: Re: [PATCH v2 1/2] x86/boot/64: Make level2_kernel_pgt pages invalid
 outside kernel area.

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.