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Subject: Re: [RFC PATCH v2 2/3] mm: make pXd_addr_end() functions page-table
 entry aware
To: Alexander Gordeev <agordeev@linux.ibm.com>,
 Michael Ellerman <mpe@ellerman.id.au>
References: <20200907180058.64880-1-gerald.schaefer@linux.ibm.com>
 <20200907180058.64880-3-gerald.schaefer@linux.ibm.com>
 <31dfb3ed-a0cc-3024-d389-ab9bd19e881f@csgroup.eu>
 <20200908074638.GA19099@oc3871087118.ibm.com>
From: Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <5d4f5546-afd0-0b8f-664d-700ae346b9ec@csgroup.eu>
Date: Tue, 8 Sep 2020 10:16:49 +0200
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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