linux-kernel - Re: [PATCH] mm/gup: fix gup_fast with dynamic page table folding

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Message-ID: <20200911194000.GB1221970@ziepe.ca>
Date:   Fri, 11 Sep 2020 16:40:00 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Vasily Gorbik <gor@...ux.ibm.com>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@...linux.org.uk>,
        Mike Rapoport <rppt@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Arnd Bergmann <arnd@...db.de>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        linux-x86 <x86@...nel.org>,
        linux-arm <linux-arm-kernel@...ts.infradead.org>,
        linux-power <linuxppc-dev@...ts.ozlabs.org>,
        linux-sparc <sparclinux@...r.kernel.org>,
        linux-um <linux-um@...ts.infradead.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Subject: Re: [PATCH] mm/gup: fix gup_fast with dynamic page table folding

On Fri, Sep 11, 2020 at 09:03:06PM +0200, Vasily Gorbik wrote:
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index e8cbc2e795d5..e899d3506671 100644
> +++ b/include/linux/pgtable.h
> @@ -1427,6 +1427,16 @@ typedef unsigned int pgtbl_mod_mask;
>  #define mm_pmd_folded(mm)	__is_defined(__PAGETABLE_PMD_FOLDED)
>  #endif
>  
> +#ifndef p4d_offset_lockless
> +#define p4d_offset_lockless(pgdp, pgd, address) p4d_offset(&pgd, address)
> +#endif
> +#ifndef pud_offset_lockless
> +#define pud_offset_lockless(p4dp, p4d, address) pud_offset(&p4d, address)
> +#endif
> +#ifndef pmd_offset_lockless
> +#define pmd_offset_lockless(pudp, pud, address) pmd_offset(&pud, address)

Needs brackets: &(pgd) 

These would probably be better as static inlines though, as only s390
compiles will type check pudp like this.

Jason