linux-kernel - Re: [PATCH] mm/zsmalloc.c: Fix zsmalloc 32-bit PAE support

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Message-ID: <20181210151506.phyjkfcg3skogtyh@kshutemo-mobl1>
Date:   Mon, 10 Dec 2018 18:15:06 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Rafael David Tinoco <rafael.tinoco@...aro.org>
Cc:     Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S . Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Minchan Kim <minchan@...nel.org>,
        Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Ram Pai <linuxram@...ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Anthony Yznaga <anthony.yznaga@...cle.com>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Joerg Roedel <jroedel@...e.de>,
        Juergen Gross <jgross@...e.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Jiri Kosina <jkosina@...e.cz>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-mips@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] mm/zsmalloc.c: Fix zsmalloc 32-bit PAE support

On Mon, Dec 10, 2018 at 12:21:05PM -0200, Rafael David Tinoco wrote:
> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> index 84bd9bdc1987..d808cfde3d19 100644
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/arch/x86/include/asm/pgtable_64_types.h
> @@ -64,8 +64,6 @@ extern unsigned int ptrs_per_p4d;
>  #define P4D_SIZE		(_AC(1, UL) << P4D_SHIFT)
>  #define P4D_MASK		(~(P4D_SIZE - 1))
>  
> -#define MAX_POSSIBLE_PHYSMEM_BITS	52
> -
>  #else /* CONFIG_X86_5LEVEL */
>  
>  /*
> @@ -154,4 +152,6 @@ extern unsigned int ptrs_per_p4d;
>  
>  #define PGD_KERNEL_START	((PAGE_SIZE / 2) / sizeof(pgd_t))
>  
> +#define MAX_POSSIBLE_PHYSMEM_BITS (pgtable_l5_enabled() ? 52 : 46)
> +

...

>  #endif /* _ASM_X86_PGTABLE_64_DEFS_H */
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 0787d33b80d8..132c20b6fd4f 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c

...

> @@ -116,6 +100,25 @@
>   */
>  #define OBJ_ALLOCATED_TAG 1
>  #define OBJ_TAG_BITS 1
> +
> +/*
> + * MAX_POSSIBLE_PHYSMEM_BITS should be defined by all archs using zsmalloc:
> + * Trying to guess it from MAX_PHYSMEM_BITS, or considering it BITS_PER_LONG,
> + * proved to be wrong by not considering PAE capabilities, or using SPARSEMEM
> + * only headers, leading to bad object encoding due to object index overflow.
> + */
> +#ifndef MAX_POSSIBLE_PHYSMEM_BITS
> + #define MAX_POSSIBLE_PHYSMEM_BITS BITS_PER_LONG
> + #error "MAX_POSSIBLE_PHYSMEM_BITS HAS to be defined by arch using zsmalloc";
> +#else
> + #ifndef CONFIG_64BIT
> +  #if (MAX_POSSIBLE_PHYSMEM_BITS >= (BITS_PER_LONG + PAGE_SHIFT - OBJ_TAG_BITS))
> +   #error "MAX_POSSIBLE_PHYSMEM_BITS is wrong for this arch";
> +  #endif
> + #endif
> +#endif
> +
> +#define _PFN_BITS (MAX_POSSIBLE_PHYSMEM_BITS - PAGE_SHIFT)
>  #define OBJ_INDEX_BITS	(BITS_PER_LONG - _PFN_BITS - OBJ_TAG_BITS)
>  #define OBJ_INDEX_MASK	((_AC(1, UL) << OBJ_INDEX_BITS) - 1)

Have you tested it with CONFIG_X86_5LEVEL=y?

ASAICS, the patch makes OBJ_INDEX_BITS and what depends from it dynamic --
it depends what paging mode we are booting in. ZS_SIZE_CLASSES depends
indirectly on OBJ_INDEX_BITS and I don't see how struct zs_pool definition
can compile with dynamic ZS_SIZE_CLASSES.

Hm?

-- 
 Kirill A. Shutemov