linux-kernel - Re: [PATCH 04/15] arm64: switch to generic version of pte allocation

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Date:   Sun, 5 May 2019 09:19:57 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greentime Hu <green.hu@...il.com>,
        Guan Xuetao <gxt@....edu.cn>, Guo Ren <guoren@...nel.org>,
        Helge Deller <deller@....de>, Ley Foon Tan <lftan@...era.com>,
        Matthew Wilcox <willy@...radead.org>,
        Matt Turner <mattst88@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Burton <paul.burton@...s.com>,
        Richard Kuo <rkuo@...eaurora.org>,
        Richard Weinberger <richard@....at>,
        Russell King <linux@...linux.org.uk>,
        Sam Creasey <sammy@...my.net>, x86@...nel.org,
        linux-alpha@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-hexagon@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-um@...ts.infradead.org,
        nios2-dev@...ts.rocketboards.org
Subject: Re: [PATCH 04/15] arm64: switch to generic version of pte allocation

On Fri, May 03, 2019 at 11:05:09AM +0100, Mark Rutland wrote:
> Hi,
> 
> On Thu, May 02, 2019 at 06:28:31PM +0300, Mike Rapoport wrote:
> > The PTE allocations in arm64 are identical to the generic ones modulo the
> > GFP flags.
> > 
> > Using the generic pte_alloc_one() functions ensures that the user page
> > tables are allocated with __GFP_ACCOUNT set.
> > 
> > The arm64 definition of PGALLOC_GFP is removed and replaced with
> > GFP_PGTABLE_USER for p[gum]d_alloc_one() and for KVM memory cache.
> > 
> > The mappings created with create_pgd_mapping() are now using
> > GFP_PGTABLE_KERNEL.
> > 
> > The conversion to the generic version of pte_free_kernel() removes the NULL
> > check for pte.
> > 
> > The pte_free() version on arm64 is identical to the generic one and
> > can be simply dropped.
> > 
> > Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> > ---
> >  arch/arm64/include/asm/pgalloc.h | 43 ++++------------------------------------
> >  arch/arm64/mm/mmu.c              |  2 +-
> >  arch/arm64/mm/pgd.c              |  4 ++--
> >  virt/kvm/arm/mmu.c               |  2 +-
> >  4 files changed, 8 insertions(+), 43 deletions(-)
> 
> [...]
> 
> > diff --git a/arch/arm64/mm/pgd.c b/arch/arm64/mm/pgd.c
> > index 289f911..2ef1a53 100644
> > --- a/arch/arm64/mm/pgd.c
> > +++ b/arch/arm64/mm/pgd.c
> > @@ -31,9 +31,9 @@ static struct kmem_cache *pgd_cache __ro_after_init;
> >  pgd_t *pgd_alloc(struct mm_struct *mm)
> >  {
> >  	if (PGD_SIZE == PAGE_SIZE)
> > -		return (pgd_t *)__get_free_page(PGALLOC_GFP);
> > +		return (pgd_t *)__get_free_page(GFP_PGTABLE_USER);
> >  	else
> > -		return kmem_cache_alloc(pgd_cache, PGALLOC_GFP);
> > +		return kmem_cache_alloc(pgd_cache, GFP_PGTABLE_USER);
> >  }
> 
> In efi_virtmap_init() we use pgd_alloc() to allocate a pgd for EFI
> runtime services, which we map with a special kernel page table.
> 
> I'm not sure if accounting that is problematic, as it's allocated in a
> kernel thread off the back of an early_initcall.

The accounting bypasses kernel threads so there should be no problem.
 
> Just to check, Is that sound, or do we need a pgd_alloc_kernel()?
> 
> Thanks,
> Mark.
> 

-- 
Sincerely yours,
Mike.