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AJvYcCXg/oVPm8NUywct+RAjdr+YWlHdGSnirRfJpmrvgZzPSWWM84DmVpJX6k6C0V6nhpVSTZhkmYhV2gf94mP4Urf7rm8= X-Gm-Message-State: AOJu0YyHuCsKv5yx7+J0zKm4JdYO+qvEgqBRw+mmpVQ7/CKcoxv78G+I DpTjpvhcvDqC85NKQL4h9iL0QvTjp4COPHCXEu6ZuoQvt/WNH6nH6XQipmv3vgbfUiyQiF6Vreu Ugs0ldeoPk4+bQpMhxwKd/wW07SsKk+VxJhjSdg== X-Google-Smtp-Source: AGHT+IG6IICf6mTVqLB93orADYYEOVxNKlJMd+eKfZHuB3dGiodlXANXWrNyQLOjhqIbklOO4rkMwE+AIB/9mOC0zmw= X-Received: by 2002:a05:6214:588a:b0:6ab:9884:1a82 with SMTP id 6a1803df08f44-6b030a9dc13mr38708276d6.51.1717632102803; Wed, 05 Jun 2024 17:01:42 -0700 (PDT) MIME-Version: 1.0 References: <20240605212146.994486-1-peterx@redhat.com> In-Reply-To: <20240605212146.994486-1-peterx@redhat.com> From: Pasha Tatashin Date: Wed, 5 Jun 2024 20:01:05 -0400 Message-ID: Subject: Re: [PATCH] mm/page_table_check: Fix crash on ZONE_DEVICE To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Dan Williams Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 0E0EC20014 X-Stat-Signature: a91j43ixshp484dxe6ojies956teiig1 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1717632103-684020 X-HE-Meta: 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 SrQrkna+ Vd8gSNp/G/tajFigAEJnz2y0tyG+EHhFb3rho0iseV5vM1PCMFC9dzBkUcr/ZQfUmZM1MOoTe9e/mIDZQbkTafpIQViEkFy/m1HMfppTFrHt6l07OEulQtZ/Lw2tDtFBhOH+wcK8uFDMygxmkwbIfnMsiYM101p8ISOSZZk8//IW3VlobnN/xhvuqY2JshwDflvn0o7R0H/yEq99xwjJjLXAHhJ35HTdRa+eK+sfb+NF8juAwc+bXAKiRY7DNiTr5LXd1vsAV7MMEJoEUe48wNz/Smxtv/4Hu6GaVSEiKN8Wy2UNqZhPvFXN6JYQ5YEypg1JNDnrRCRr9tgsTTDQ7WDMuJb78+1d1EQAhxXxzn+Cr69rNy8BiSAYSJFQpgy4UABT9m6ZeX6+bnv1tCEt1QHT/0JB4QVJTcs8idD5rNmzRR/VbJUk0X+e2Pw== 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: List-Subscribe: List-Unsubscribe: On Wed, Jun 5, 2024 at 5:21=E2=80=AFPM Peter Xu wrote: > > Not all pages may apply to pgtable check. One example is ZONE_DEVICE > pages: they map PFNs directly, and they don't allocate page_ext at all ev= en > if there's struct page around. One may reference devm_memremap_pages(). > > When both ZONE_DEVICE and page-table-check enabled, then try to map some > dax memories, one can trigger kernel bug constantly now when the kernel w= as > trying to inject some pfn maps on the dax device: > > kernel BUG at mm/page_table_check.c:55! > > While it's pretty legal to use set_pxx_at() for ZONE_DEVICE pages for pag= e > fault resolutions, skip all the checks if page_ext doesn't even exist in > pgtable checker, which applies to ZONE_DEVICE but maybe more. Thank you for reporting this bug. A few comments below: > > Cc: Dan Williams > Cc: Pasha Tatashin > Signed-off-by: Peter Xu > --- > mm/page_table_check.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/mm/page_table_check.c b/mm/page_table_check.c > index 4169576bed72..509c6ef8de40 100644 > --- a/mm/page_table_check.c > +++ b/mm/page_table_check.c > @@ -73,6 +73,9 @@ static void page_table_check_clear(unsigned long pfn, u= nsigned long pgcnt) > page =3D pfn_to_page(pfn); > page_ext =3D page_ext_get(page); > > + if (!page_ext) > + return; I would replace the above with the following, here and in other places: if (!page_ext) { WARN_ONCE(!is_zone_device_page(page), "page_ext is missing for a non-device page\n"); return; } > + > BUG_ON(PageSlab(page)); > anon =3D PageAnon(page); > > @@ -110,6 +113,9 @@ static void page_table_check_set(unsigned long pfn, u= nsigned long pgcnt, > page =3D pfn_to_page(pfn); > page_ext =3D page_ext_get(page); > > + if (!page_ext) > + return; > + > BUG_ON(PageSlab(page)); > anon =3D PageAnon(page); > > @@ -140,7 +146,10 @@ void __page_table_check_zero(struct page *page, unsi= gned int order) > BUG_ON(PageSlab(page)); > > page_ext =3D page_ext_get(page); > - BUG_ON(!page_ext); > + > + if (!page_ext) > + return; > + > for (i =3D 0; i < (1ul << order); i++) { > struct page_table_check *ptc =3D get_page_table_check(pag= e_ext); > > -- > 2.45.0 >