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Subject: Re: [PATCH 1/4] hugetlbfs: add arch_hugetlb_valid_size
To:     Mike Kravetz <mike.kravetz@oracle.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
        linux-s390@vger.kernel.org, sparclinux@vger.kernel.org,
        linux-doc@vger.kernel.org
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        "David S . Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Longpeng <longpeng2@huawei.com>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20200318220634.32100-1-mike.kravetz@oracle.com>
 <20200318220634.32100-2-mike.kravetz@oracle.com>
From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <831a0773-1ba6-4d72-44b9-7472123b8528@intel.com>
Date:   Wed, 18 Mar 2020 15:15:43 -0700
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In-Reply-To: <20200318220634.32100-2-mike.kravetz@oracle.com>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Mike,

The series looks like a great idea to me.  One nit on the x86 bits,
though...

> diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
> index 5bfd5aef5378..51e6208fdeec 100644
> --- a/arch/x86/mm/hugetlbpage.c
> +++ b/arch/x86/mm/hugetlbpage.c
> @@ -181,16 +181,25 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>  #endif /* CONFIG_HUGETLB_PAGE */
>  
>  #ifdef CONFIG_X86_64
> +bool __init arch_hugetlb_valid_size(unsigned long long size)
> +{
> +	if (size == PMD_SIZE)
> +		return true;
> +	else if (size == PUD_SIZE && boot_cpu_has(X86_FEATURE_GBPAGES))
> +		return true;
> +	else
> +		return false;
> +}

I'm pretty sure it's possible to have a system without 2M/PMD page
support.  We even have a handy-dandy comment about it in
arch/x86/include/asm/required-features.h:

	#ifdef CONFIG_X86_64
	#ifdef CONFIG_PARAVIRT
	/* Paravirtualized systems may not have PSE or PGE available */
	#define NEED_PSE        0
	...

I *think* you need an X86_FEATURE_PSE check here to be totally correct.

	if (size == PMD_SIZE && cpu_feature_enabled(X86_FEATURE_PSE))
		return true;

BTW, I prefer cpu_feature_enabled() to boot_cpu_has() because it
includes disabled-features checking.  I don't think any of it matters
for these specific features, but I generally prefer it on principle.