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AJvYcCU+MdGavl256cwNCBHIIQehGz8a9IlK5sB8b2SDq2vzEWgSELFAAOOHMWnTZFJqW6M8iWCjhcTA4Zp9IMoU8EjrlkM= X-Gm-Message-State: AOJu0YyQwGly/Th6MoYEPI4trAaFYGH1ugVicWlSr32BYUYsofkWzCef rVAWBQRENzmhCVXwBU3opsn6qWuK3vnaAtPiO/ukJbHtNoaA6oOsVfSFShU+kkbGuhYfIMG+hOr XC2ckIdAtUFHy5//wPaZk1p5YXGRw9F1D3CRCig== X-Google-Smtp-Source: AGHT+IFR4OHciC4416nU/Vadzzwje6/rqkHG0oe8lwzmS6LuTsftY2iNl1Gq5BEhPp6lD/4SkUqnuWlmnfdeVgnr8Jc= X-Received: by 2002:a05:620a:a19:b0:790:f843:db57 with SMTP id af79cd13be357-794ab0f8b0bmr65876085a.58.1716506637454; Thu, 23 May 2024 16:23:57 -0700 (PDT) MIME-Version: 1.0 References: <20240523132139.289719-1-peterx@redhat.com> In-Reply-To: <20240523132139.289719-1-peterx@redhat.com> From: Pasha Tatashin Date: Thu, 23 May 2024 19:23:19 -0400 Message-ID: Subject: Re: [PATCH] mm/debug_vm_pgtable: Drop RANDOM_ORVALUE trick To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , David Hildenbrand , "Aneesh Kumar K . V" , Gavin Shan , Anshuman Khandual , Mikhail Gavrilov Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 5DF6B40003 X-Stat-Signature: 9qiq6sazjj6kshmyjm44orbz3jce6z68 X-HE-Tag: 1716506638-342951 X-HE-Meta: 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 OAkzRMbT 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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: On Thu, May 23, 2024 at 9:21=E2=80=AFAM Peter Xu wrote: > > Macro RANDOM_ORVALUE was used to make sure the pgtable entry will be > populated with !none data in clear tests. > > The RANDOM_ORVALUE tried to cover mostly all the bits in a pgtable entry, > even if there's no discussion on whether all the bits will be vaild. Bot= h > S390 and PPC64 have their own masks to avoid touching some bits. Now it'= s > the turn for x86_64. > > The issue is there's a recent report from Mikhail Gavrilov showing that > this can cause a warning with the newly added pte set check in commit > 8430557fc5 on writable v.s. userfaultfd-wp bit, even though the check > itself was valid, the random pte is not. We can choose to mask more bits > out. > > However the need to have such random bits setup is questionable, as now > it's already guaranteed to be true on below: > > - For pte level, the pgtable entry will be installed with value from > pfn_pte(), where pfn points to a valid page. Hence the pte will be > !none already if populated with pfn_pte(). > > - For upper-than-pte level, the pgtable entry should contain a director= y > entry always, which is also !none. > > All the cases look like good enough to test a pxx_clear() helper. Instea= d > of extending the bitmask, drop the "set random bits" trick completely. A= dd > some warning guards to make sure the entries will be !none before clear()= . > > Cc: David Hildenbrand > Cc: Pavel Tatashin > Cc: Aneesh Kumar K.V > Cc: Gavin Shan > Cc: Anshuman Khandual > Reported-by: Mikhail Gavrilov > Tested-by: Mikhail Gavrilov > Link: https://lore.kernel.org/r/CABXGCsMB9A8-X+Np_Q+fWLURYL_0t3Y-MdoNabDM= -Lzk58-DGA@mail.gmail.com > Signed-off-by: Peter Xu > --- > mm/debug_vm_pgtable.c | 31 +++++-------------------------- > 1 file changed, 5 insertions(+), 26 deletions(-) Reviewed-by: Pasha Tatashin