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

From: Mark Rutland <mark.rutland@arm.com>
To: Mike Rapoport <rppt@linux.ibm.com>
Cc: Michal Hocko <mhocko@suse.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Palmer Dabbelt <palmer@sifive.com>,
	linux-mips@vger.kernel.org, Guo Ren <guoren@kernel.org>,
	linux-hexagon@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-arch@vger.kernel.org, Michael Ellerman <mpe@ellerman.id.au>,
	Helge Deller <deller@gmx.de>,
	x86@kernel.org, Russell King <linux@armlinux.org.uk>,
	Matthew Wilcox <willy@infradead.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Matt Turner <mattst88@gmail.com>, Sam Creasey <sammy@sammy.net>,
	Arnd Bergmann <arnd@arndb.de>,
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	Greentime Hu <green.hu@gmail.com>,
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	linux-arm-kernel@lists.infradead.org,
	linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org,
	Richard Kuo <rkuo@codeaurora.org>,
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	Andrew Morton <akpm@linux-foundation.org>,
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Subject: Re: [PATCH 04/15] arm64: switch to generic version of pte allocation
Date: Fri, 3 May 2019 11:05:09 +0100	[thread overview]
Message-ID: <20190503100508.GB47811@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <1556810922-20248-5-git-send-email-rppt@linux.ibm.com>

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@linux.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.

Just to check, Is that sound, or do we need a pgd_alloc_kernel()?

Thanks,
Mark.

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