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[91.12.96.65]) by smtp.gmail.com with ESMTPSA id 61sm4080214wrl.94.2021.09.14.10.23.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Sep 2021 10:23:37 -0700 (PDT) Subject: Re: [PATCH resend RFC 7/9] s390/mm: no need for pte_alloc_map_lock() if we know the pmd is present To: Claudio Imbrenda Cc: linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, Christian Borntraeger , Janosch Frank , Cornelia Huck , Heiko Carstens , Vasily Gorbik , Niklas Schnelle , Gerald Schaefer , Ulrich Weigand References: <20210909162248.14969-1-david@redhat.com> <20210909162248.14969-8-david@redhat.com> <20210914185449.42d7d5ca@p-imbrenda> From: David Hildenbrand Organization: Red Hat Message-ID: <5a572489-a6d6-aaf4-098a-a8059f9b12f0@redhat.com> Date: Tue, 14 Sep 2021 19:23:36 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210914185449.42d7d5ca@p-imbrenda> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=SZy8xrWi; spf=none (imf30.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: r93r8xhe7dr3kmopzsu6ddrk4dxet4rg X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 0F1D9E0016B0 X-HE-Tag: 1631640220-954187 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 14.09.21 18:54, Claudio Imbrenda wrote: > On Thu, 9 Sep 2021 18:22:46 +0200 > David Hildenbrand wrote: > >> pte_map_lock() is sufficient. > > Can you explain the difference and why it is enough? I didn't repeat the $subject: "No need for pte_alloc_map_lock() if we know the pmd is present; pte_map_lock() is sufficient, because there isn't anything to allocate." > >> >> Signed-off-by: David Hildenbrand >> --- >> arch/s390/mm/pgtable.c | 15 +++------------ >> 1 file changed, 3 insertions(+), 12 deletions(-) >> >> diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c >> index 5fb409ff7842..4e77b8ebdcc5 100644 >> --- a/arch/s390/mm/pgtable.c >> +++ b/arch/s390/mm/pgtable.c >> @@ -814,10 +814,7 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr, >> } >> spin_unlock(ptl); >> >> - ptep = pte_alloc_map_lock(mm, pmdp, addr, &ptl); >> - if (unlikely(!ptep)) >> - return -EFAULT; >> - >> + ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); >> new = old = pgste_get_lock(ptep); >> pgste_val(new) &= ~(PGSTE_GR_BIT | PGSTE_GC_BIT | >> PGSTE_ACC_BITS | PGSTE_FP_BIT); >> @@ -912,10 +909,7 @@ int reset_guest_reference_bit(struct mm_struct *mm, unsigned long addr) >> } >> spin_unlock(ptl); >> >> - ptep = pte_alloc_map_lock(mm, pmdp, addr, &ptl); >> - if (unlikely(!ptep)) >> - return -EFAULT; >> - >> + ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); >> new = old = pgste_get_lock(ptep); >> /* Reset guest reference bit only */ >> pgste_val(new) &= ~PGSTE_GR_BIT; >> @@ -977,10 +971,7 @@ int get_guest_storage_key(struct mm_struct *mm, unsigned long addr, >> } >> spin_unlock(ptl); >> >> - ptep = pte_alloc_map_lock(mm, pmdp, addr, &ptl); >> - if (unlikely(!ptep)) >> - return -EFAULT; >> - >> + ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); >> pgste = pgste_get_lock(ptep); >> *key = (pgste_val(pgste) & (PGSTE_ACC_BITS | PGSTE_FP_BIT)) >> 56; >> paddr = pte_val(*ptep) & PAGE_MASK; > -- Thanks, David / dhildenb