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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: B0BCE4000B X-Rspamd-Server: rspam03 X-Stat-Signature: jft7bz4m5k9ua1uhq7qr4ew7uburhqhh X-HE-Tag: 1760595309-492124 X-HE-Meta: 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 NHKtUR4f LPsGoORFjXjQzB13Z4yq74hIpIVHQ6kgq/mMNl/nNGTLULDtjPjeKbfsjiiUN/NLKNowH9QlF4oJj3fi8HqGDdUW7TGmOkHOt6mobpPd6sFfX1+ukcIHzBxASERTSh8g4xRF6snTdf+2EPjGaYJtah/+YGRxJqz5HV29NC0k2jdx+7ixkgJ8lbBuAoPMQWrCbh7uMqCBvZNAmoZY/2Xn3cuRDVRoQ4CrUfulWkGxIgecdskk= 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 16/10/25 11:29 am, Lance Yang wrote: > > > On 2025/10/16 13:34, Dev Jain wrote: >> >> On 16/10/25 9:06 am, Lance Yang wrote: >>> From: Lance Yang >>> >>> A non-present entry, like a swap PTE, contains completely different >>> data >>> (swap type and offset). pte_pfn() doesn't know this, so if we feed it a >>> non-present entry, it will spit out a junk PFN. >>> >>> What if that junk PFN happens to match the zeropage's PFN by sheer >>> chance? While really unlikely, this would be really bad if it did. >>> >>> So, let's fix this potential bug by ensuring all calls to is_zero_pfn() >>> in khugepaged.c are properly guarded by a pte_present() check. >>> >>> Suggested-by: Lorenzo Stoakes >>> Signed-off-by: Lance Yang >>> --- >> >> Thanks, I missed this. > > Me too ... > >> >>>   mm/khugepaged.c | 13 ++++++++----- >>>   1 file changed, 8 insertions(+), 5 deletions(-) >>> >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>> index d635d821f611..0341c3d13e9e 100644 >>> --- a/mm/khugepaged.c >>> +++ b/mm/khugepaged.c >>> @@ -516,7 +516,7 @@ static void release_pte_pages(pte_t *pte, pte_t >>> *_pte, >>>           pte_t pteval = ptep_get(_pte); >>>           unsigned long pfn; >>> -        if (pte_none(pteval)) >>> +        if (!pte_present(pteval)) >> >> There should be no chance that we end up with a pteval which is not >> none *and* >> not present, if you look at the callers of release_pte_pages. So >> perhaps we >> should keep this either the same, or, after "if(pte_none(pteval))", do a >> WARN_ON_ONCE(!pte_present(pteval))? > > Good catch! Yeah, but I'd rather not rely on the callers ... > > Wouldn't it just be simpler and safer to always have is_zero_pfn() > guarded > by pte_present()? > > I don't have a strong opinon here, though ;p Yeah same, I think we can leave it to what you have done. > > Dev, Thanks! >