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[2003:cb:c707:6e00:ff02:ec7a:ded5:ec1e]) by smtp.gmail.com with ESMTPSA id c7-20020a05600c0a4700b003c6bbe910fdsm1908482wmq.9.2023.01.05.00.39.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Jan 2023 00:39:35 -0800 (PST) Message-ID: Date: Thu, 5 Jan 2023 09:39:34 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH 1/3] mm/hugetlb: Pre-allocate pgtable pages for uffd wr-protects To: Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Mike Kravetz , Muchun Song , Nadav Amit , Andrea Arcangeli , James Houghton , Axel Rasmussen , Andrew Morton , linux-stable References: <20230104225207.1066932-1-peterx@redhat.com> <20230104225207.1066932-2-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230104225207.1066932-2-peterx@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C64474000A X-Stat-Signature: z1meux1m83qere5p8ru8bjrzgbn99qwf X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1672908070-589251 X-HE-Meta: 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 TwdcOlkQ l5UXcs3F2V/cX7C8exvirwS4rnY0ZGyJgWx9UZfpZRo1/bzGgrSU4+xbjh9cSauLBo4/cjKy44ayF5ykWzem8VuSKbHsF06gLi18KTqi63+PLCpkCnfn0mSIqmjkwXM6/uI+Dm71UffpLWU6SnrvMPFa4sT9ybx0ZS0mg4v1Mpv+ZrjB/NM3NjIQp42d0LeYv1Nq7v5hn4Yy0rO6zuQ9NVUBRbQ== 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 04.01.23 23:52, Peter Xu wrote: > Userfaultfd-wp uses pte markers to mark wr-protected pages for both shmem > and hugetlb. Shmem has pre-allocation ready for markers, but hugetlb path > was overlooked. > > Doing so by calling huge_pte_alloc() if the initial pgtable walk fails to > find the huge ptep. It's possible that huge_pte_alloc() can fail with high > memory pressure, in that case stop the loop immediately and fail silently. > This is not the most ideal solution but it matches with what we do with > shmem meanwhile it avoids the splat in dmesg. > > Cc: linux-stable # 5.19+ > Fixes: 60dfaad65aa9 ("mm/hugetlb: allow uffd wr-protect none ptes") > Reported-by: James Houghton > Signed-off-by: Peter Xu > --- > mm/hugetlb.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index bf7a1f628357..017d9159cddf 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -6649,8 +6649,17 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, > spinlock_t *ptl; > ptep = hugetlb_walk(vma, address, psize); if (!ptep && likely(!uffd_wp)) { /* Nothing to protect. */ address |= last_addr_mask; continue; } else if (!ptep) { ... } Might look slightly more readable would minimize changes. This should work, so Acked-by: David Hildenbrand > if (!ptep) { > - address |= last_addr_mask; > - continue; > + if (!uffd_wp) { > + address |= last_addr_mask; > + continue; > + } > + /* > + * Userfaultfd wr-protect requires pgtable > + * pre-allocations to install pte markers. > + */ > + ptep = huge_pte_alloc(mm, vma, address, psize); > + if (!ptep) > + break; > } > ptl = huge_pte_lock(h, mm, ptep); > if (huge_pmd_unshare(mm, vma, address, ptep)) { -- Thanks, David / dhildenb