linux-kernel - Re: [RFC PATCH v2 2/3] mm: make pXd_addr_end() functions page-table entry aware

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Message-ID: <5d4f5546-afd0-0b8f-664d-700ae346b9ec@csgroup.eu>
Date:   Tue, 8 Sep 2020 10:16:49 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Alexander Gordeev <agordeev@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-mm <linux-mm@...ck.org>, Paul Mackerras <paulus@...ba.org>,
        linux-sparc <sparclinux@...r.kernel.org>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Richard Weinberger <richard@....at>,
        linux-x86 <x86@...nel.org>, Russell King <linux@...linux.org.uk>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Arnd Bergmann <arnd@...db.de>, Jeff Dike <jdike@...toit.com>,
        linux-um <linux-um@...ts.infradead.org>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm <linux-arm-kernel@...ts.infradead.org>,
        linux-power <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [RFC PATCH v2 2/3] mm: make pXd_addr_end() functions page-table
 entry aware



Le 08/09/2020 à 09:46, Alexander Gordeev a écrit :
> On Tue, Sep 08, 2020 at 07:14:38AM +0200, Christophe Leroy wrote:
>> You forgot arch/powerpc/mm/book3s64/subpage_prot.c it seems.
> 
> Yes, and also two more sources :/
> 	arch/powerpc/mm/kasan/8xx.c
> 	arch/powerpc/mm/kasan/kasan_init_32.c
> 
> But these two are not quite obvious wrt pgd_addr_end() used
> while traversing pmds. Could you please clarify a bit?
> 
> 
> diff --git a/arch/powerpc/mm/kasan/8xx.c b/arch/powerpc/mm/kasan/8xx.c
> index 2784224..89c5053 100644
> --- a/arch/powerpc/mm/kasan/8xx.c
> +++ b/arch/powerpc/mm/kasan/8xx.c
> @@ -15,8 +15,8 @@
>   	for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pmd += 2, block += SZ_8M) {
>   		pte_basic_t *new;
>   
> -		k_next = pgd_addr_end(k_cur, k_end);
> -		k_next = pgd_addr_end(k_next, k_end);
> +		k_next = pmd_addr_end(k_cur, k_end);
> +		k_next = pmd_addr_end(k_next, k_end);

No, I don't think so.
On powerpc32 we have only two levels, so pgd and pmd are more or less 
the same.
But pmd_addr_end() as defined in include/asm-generic/pgtable-nopmd.h is 
a no-op, so I don't think it will work.

It is likely that this function should iterate on pgd, then you get pmd 
= pmd_offset(pud_offset(p4d_offset(pgd)));

>   		if ((void *)pmd_page_vaddr(*pmd) != kasan_early_shadow_pte)
>   			continue;
>   
> diff --git a/arch/powerpc/mm/kasan/kasan_init_32.c b/arch/powerpc/mm/kasan/kasan_init_32.c
> index fb29404..3f7d6dc6 100644
> --- a/arch/powerpc/mm/kasan/kasan_init_32.c
> +++ b/arch/powerpc/mm/kasan/kasan_init_32.c
> @@ -38,7 +38,7 @@ int __init kasan_init_shadow_page_tables(unsigned long k_start, unsigned long k_
>   	for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pmd++) {
>   		pte_t *new;
>   
> -		k_next = pgd_addr_end(k_cur, k_end);
> +		k_next = pmd_addr_end(k_cur, k_end);

Same here I get, iterate on pgd then get pmd = 
pmd_offset(pud_offset(p4d_offset(pgd)));

>   		if ((void *)pmd_page_vaddr(*pmd) != kasan_early_shadow_pte)
>   			continue;
>   
> @@ -196,7 +196,7 @@ void __init kasan_early_init(void)
>   	kasan_populate_pte(kasan_early_shadow_pte, PAGE_KERNEL);
>   
>   	do {
> -		next = pgd_addr_end(addr, end);
> +		next = pmd_addr_end(addr, end);
>   		pmd_populate_kernel(&init_mm, pmd, kasan_early_shadow_pte);
>   	} while (pmd++, addr = next, addr != end);
>   
> 

Christophe