linux-kernel - Re: [PATCH v2 04/13] arm64: decouple early fixmap init from linear mapping

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Message-ID: <CAKv+Gu9CRMqtDzHmdk3ZHDzA=12KNua9zKJXzz3Ug3HN9yybBA@mail.gmail.com>
Date:	Fri, 8 Jan 2016 13:05:14 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	kernel-hardening@...ts.openwall.com,
	Will Deacon <will.deacon@....com>,
	Mark Rutland <mark.rutland@....com>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Kees Cook <keescook@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Sharma Bhupesh <bhupesh.sharma@...escale.com>,
	Stuart Yoder <stuart.yoder@...escale.com>,
	Marc Zyngier <marc.zyngier@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>
Subject: Re: [PATCH v2 04/13] arm64: decouple early fixmap init from linear mapping

On 8 January 2016 at 13:00, Catalin Marinas <catalin.marinas@....com> wrote:
> On Wed, Dec 30, 2015 at 04:26:03PM +0100, Ard Biesheuvel wrote:
>> @@ -583,33 +555,42 @@ void __init early_fixmap_init(void)
>>       unsigned long addr = FIXADDR_START;
>>
>>       pgd = pgd_offset_k(addr);
>> -     pgd_populate(&init_mm, pgd, bm_pud);
>> -     pud = pud_offset(pgd, addr);
>> -     pud_populate(&init_mm, pud, bm_pmd);
>> -     pmd = pmd_offset(pud, addr);
>> -     pmd_populate_kernel(&init_mm, pmd, bm_pte);
>> +#if CONFIG_PGTABLE_LEVELS > 3
>> +     if (pgd_none(*pgd)) {
>> +             static pud_t bm_pud[PTRS_PER_PUD] __pgdir;
>> +
>> +             pgd_populate(&init_mm, pgd, bm_pud);
>> +             memblock_reserve(__pa(bm_pud), sizeof(bm_pud));
>> +     }
>> +     pud = (pud_t *)__phys_to_kimg(pud_offset_phys(pgd, addr));
>> +#else
>> +     pud = (pud_t *)pgd;
>> +#endif
>> +#if CONFIG_PGTABLE_LEVELS > 2
>> +     if (pud_none(*pud)) {
>> +             static pmd_t bm_pmd[PTRS_PER_PMD] __pgdir;
>> +
>> +             pud_populate(&init_mm, pud, bm_pmd);
>> +             memblock_reserve(__pa(bm_pmd), sizeof(bm_pmd));
>> +     }
>> +     pmd = (pmd_t *)__phys_to_kimg(pmd_offset_phys(pud, addr));
>> +#else
>> +     pmd = (pmd_t *)pud;
>> +#endif
>> +     if (pmd_none(*pmd)) {
>> +             static pte_t bm_pte[PTRS_PER_PTE] __pgdir;
>> +
>> +             pmd_populate_kernel(&init_mm, pmd, bm_pte);
>> +             memblock_reserve(__pa(bm_pte), sizeof(bm_pte));
>> +     }
>> +     __fixmap_pte = (pte_t *)__phys_to_kimg(pmd_page_paddr(*pmd));
>
> I haven't tried but could you not avoid the #if and just rely on the
> pud_none() etc. definitions to be 0 and the compiler+linker optimising
> the irrelevant code out?
>

I tried but it requires some tinkering so I gave up. I can have
another go based on the latest version (which will look a bit
different)