linux-kernel - Re: [PATCH 1/4] hugetlbfs: add arch_hugetlb_valid

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Date:   Wed, 25 Mar 2020 10:38:40 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>, Mike Kravetz <mike.kravetz@...cle.com>,
        Dave Hansen <dave.hansen@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-doc@...r.kernel.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        "David S.Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/4] hugetlbfs: add arch_hugetlb_valid_size



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.