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 JnGQbQki 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 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: Pasha Tatashin wrote: > On Wed, Jun 5, 2024 at 5:21 PM 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 even > > 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 was > > 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 page > > 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, unsigned long pgcnt) > > page = pfn_to_page(pfn); > > page_ext = 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; > } Hmm, but this function is silent for the !pfn_valid(@pfn) case, and the old cold has BUG_ON(!page_ext). So we know the caller is not being careful about @pfn, and existing code is likely avoiding the BUG_ON(). The justification for the WARN_ONCE(), or maybe VM_WARN_ONCE(), would be if there is a high likelihood that ongoing kernel changes introduce more pfn_valid() but not page_ext covered pages? Is that a realistic scenario?