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Mon, 07 Dec 2020 03:34:40 -0800 (PST) Received: from localhost.localdomain ([203.205.141.39]) by smtp.gmail.com with ESMTPSA id d4sm14219822pfo.127.2020.12.07.03.34.37 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 07 Dec 2020 03:34:39 -0800 (PST) From: yulei.kernel@gmail.com X-Google-Original-From: yuleixzhang@tencent.com To: linux-mm@kvack.org, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, naoya.horiguchi@nec.com, viro@zeniv.linux.org.uk, pbonzini@redhat.com Cc: joao.m.martins@oracle.com, rdunlap@infradead.org, sean.j.christopherson@intel.com, xiaoguangrong.eric@gmail.com, kernellwp@gmail.com, lihaiwei.kernel@gmail.com, Yulei Zhang , Chen Zhuo Subject: [RFC V2 18/37] mm: follow_pmd_mask() for dmem huge pmd Date: Mon, 7 Dec 2020 19:31:11 +0800 Message-Id: <1401155e1db8221b892fb935204ad2d358c2808f.1607332046.git.yuleixzhang@tencent.com> X-Mailer: git-send-email 2.28.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable 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: From: Yulei Zhang While follow_pmd_mask(), dmem huge pmd should be recognized and return error pointer of '-EEXIST' to indicate that proper page table entry exist= s in pmd special but no corresponding struct page, because dmem page means non struct page backend. We update pmd if foll_flags takes FOLL_TOUCH. Signed-off-by: Chen Zhuo Signed-off-by: Yulei Zhang --- mm/gup.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) diff --git a/mm/gup.c b/mm/gup.c index 98eb8e6..ad1aede 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -387,6 +387,42 @@ static int follow_pfn_pte(struct vm_area_struct *vma= , unsigned long address, return -EEXIST; } =20 +static struct page * +follow_special_pmd(struct vm_area_struct *vma, unsigned long address, + pmd_t *pmd, unsigned int flags) +{ + spinlock_t *ptl; + + if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd)) + /* Avoid special (like zero) pages in core dumps */ + return ERR_PTR(-EFAULT); + + /* No page to get reference */ + if (flags & FOLL_GET) + return ERR_PTR(-EFAULT); + + if (flags & FOLL_TOUCH) { + pmd_t _pmd; + + ptl =3D pmd_lock(vma->vm_mm, pmd); + if (!pmd_special(*pmd)) { + spin_unlock(ptl); + return NULL; + } + _pmd =3D pmd_mkyoung(*pmd); + if (flags & FOLL_WRITE) + _pmd =3D pmd_mkdirty(_pmd); + if (pmdp_set_access_flags(vma, address & HPAGE_PMD_MASK, + pmd, _pmd, + flags & FOLL_WRITE)) + update_mmu_cache_pmd(vma, address, pmd); + spin_unlock(ptl); + } + + /* Proper page table entry exists, but no corresponding struct page */ + return ERR_PTR(-EEXIST); +} + /* * FOLL_FORCE can write to even unwritable pte's, but only * after we've gone through a COW cycle and they are dirty. @@ -571,6 +607,12 @@ static struct page *follow_pmd_mask(struct vm_area_s= truct *vma, return page; return no_page_table(vma, flags); } + if (pmd_special(*pmd)) { + page =3D follow_special_pmd(vma, address, pmd, flags); + if (page) + return page; + return no_page_table(vma, flags); + } if (is_hugepd(__hugepd(pmd_val(pmdval)))) { page =3D follow_huge_pd(vma, address, __hugepd(pmd_val(pmdval)), flags, --=20 1.8.3.1