linux-kernel - Re: [PATCH] parisc: fix map_pages() to actually populate upper directory

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Date:   Thu, 9 Jan 2020 07:50:55 +0100
From:   Helge Deller <deller@....de>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>, linux-parisc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Mike Rapoport <rppt@...ux.ibm.com>,
        Meelis Roos <mroos@...ux.ee>, Jeroen Roovers <jer@...too.org>,
        Mikulas Patocka <mpatocka@...hat.com>
Subject: Re: [PATCH] parisc: fix map_pages() to actually populate upper
 directory

> The commit d96885e277b5 ("parisc: use pgtable-nopXd instead of
> 4level-fixup") converted PA-RISC to use folded page tables, but it missed
> the conversion of pgd_populate() to pud_populate() in maps_pages()
> function. This caused the upper page table directory to remain empty and
> the system would crash as a result.
>
> Using pud_populate() that actually populates the page table instead of
> dummy pgd_populate() fixes the issue.
> ...
> diff --git a/arch/parisc/mm/init.c b/arch/parisc/mm/init.c
> index ddca8287d43b..354cf060b67f 100644
> --- a/arch/parisc/mm/init.c
> +++ b/arch/parisc/mm/init.c
> @@ -401,7 +401,7 @@ static void __init map_pages(unsigned long start_vaddr,
>  			pmd = (pmd_t *) __pa(pmd);
>  		}
>
> -		pgd_populate(NULL, pg_dir, __va(pmd));
> +		pud_populate(NULL, (pud_t *)pg_dir, __va(pmd));
>  #endif

Wouldn't the untested patch below be more clean?

Helge

diff --git a/arch/parisc/mm/init.c b/arch/parisc/mm/init.c
index ddca8287d43b..73de58f31f5f 100644
--- a/arch/parisc/mm/init.c
+++ b/arch/parisc/mm/init.c
@@ -387,6 +387,8 @@ static void __init map_pages(unsigned long start_vaddr,
 #if PTRS_PER_PMD == 1
 		pmd = (pmd_t *)__pa(pg_dir);
 #else
+		p4d_t *p4d;
+		pud_t *pud;
 		pmd = (pmd_t *)pgd_address(*pg_dir);

 		/*
@@ -401,7 +403,9 @@ static void __init map_pages(unsigned long start_vaddr,
 			pmd = (pmd_t *) __pa(pmd);
 		}

-		pgd_populate(NULL, pg_dir, __va(pmd));
+		p4d = p4d_offset(pg_dir, vaddr);
+		pud = pud_offset(p4d, vaddr);
+		pud_populate(NULL, pud, __va(pmd));
 #endif
 		pg_dir++;