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Subject: Re: [PATCH 1/4] hugetlbfs: add arch_hugetlb_valid_size
To:     "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@huawei.com>, Mike Kravetz <mike.kravetz@oracle.com>,
        Dave Hansen <dave.hansen@intel.com>, linux-mm@kvack.org,
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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>,
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        Albert Ou <aou@eecs.berkeley.edu>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Vasily Gorbik <gor@linux.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>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20200318220634.32100-1-mike.kravetz@oracle.com>
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Date:   Wed, 25 Mar 2020 10:38:40 +0100
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On 25.03.20 03:58, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:
[...]
> Hi Mike,
> 
> Inspired by Dave's opinion, it seems the x86-specific hugepages_supported should
> also need to use cpu_feature_enabled instead.
> 
> Also, I wonder if the hugepages_supported is correct ? There're two arch
> specific hugepages_supported:
> x86:
> #define hugepages_supported() boot_cpu_has(X86_FEATURE_PSE)
> and
> s390:
> #define hugepages_supported() (MACHINE_HAS_EDAT1)
> 
> Is it possible that x86 has X86_FEATURE_GBPAGES but hasn't X86_FEATURE_GBPAGES
> or s390 has MACHINE_HAS_EDAT2 but hasn't MACHINE_HAS_EDAT1 ?

The s390 architecture says that 

When EDAT-2 applies, the following function is available in the DAT process:
 - EDAT-1 applies.
[..]

So if the machine has EDAT-2 it also has EDAT-1.