Message-ID: <5447825B.5040608@redhat.com>
Date: Wed, 22 Oct 2014 12:09:31 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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To: Dominik Dingel <dingel@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@suse.cz>,
        Dave Hansen <dave.hansen@intel.com>, Rik van Riel <riel@redhat.com>
CC: Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@amacapital.net>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Bob Liu <lliubbo@gmail.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Cornelia Huck <cornelia.huck@de.ibm.com>,
        Gleb Natapov <gleb@kernel.org>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        "H. Peter Anvin" <hpa@linux.intel.com>,
        Hugh Dickins <hughd@google.com>, Ingo Molnar <mingo@kernel.org>,
        Jianyu Zhan <nasa4836@gmail.com>, Johannes Weiner <hannes@cmpxchg.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Konstantin Weitz <konstantin.weitz@gmail.com>, kvm@vger.kernel.org,
        linux390@de.ibm.com, linux-kernel@vger.kernel.org,
        linux-s390@vger.kernel.org,
        Martin Schwidefsky <schwidefsky@de.ibm.com>
Subject: Re: [PATCH 3/4] s390/mm: prevent and break zero page mappings in
 case of storage keys
References: <1413966624-12447-1-git-send-email-dingel@linux.vnet.ibm.com> <1413966624-12447-4-git-send-email-dingel@linux.vnet.ibm.com>
In-Reply-To: <1413966624-12447-4-git-send-email-dingel@linux.vnet.ibm.com>
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On 10/22/2014 10:30 AM, Dominik Dingel wrote:
> As use_skey is already the condition on which we call s390_enable_skey
> we need to introduce a new flag for the mm->context on which we decide
> if zero page mapping is allowed.

Can you explain better why "mm->context.use_skey = 1" cannot be done
before the walk_page_range?  Where does the walk or __s390_enable_skey
or (after the next patch) ksm_madvise rely on
"mm->context.forbids_zeropage && !mm->context.use_skey"?

The only reason I can think of, is that the next patch does not reset
"mm->context.forbids_zeropage" to 0 if the ksm_madvise fails.  Why
doesn't it do that---or is it a bug?

Thanks, and sorry for the flurry of questions! :)

Paolo
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