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Thu, 10 Aug 2023 00:15:17 -0700 (PDT) MIME-Version: 1.0 References: <20230809164633.1556126-1-alexghiti@rivosinc.com> <20230809114651.eb690e5bd4c60b075eb3111b@linux-foundation.org> In-Reply-To: <20230809114651.eb690e5bd4c60b075eb3111b@linux-foundation.org> From: Alexandre Ghiti Date: Thu, 10 Aug 2023 09:15:06 +0200 Message-ID: Subject: Re: [PATCH -fixes] mm: Add a call to flush_cache_vmap() in vmap_pfn() To: Andrew Morton Cc: Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dylan Jhong Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 08292140031 X-Stat-Signature: gybihx75aqaqxe1tzezmhqa557mthub3 X-HE-Tag: 1691651718-529172 X-HE-Meta: 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 MGZdGLKu 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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: Hi Andrew, On Wed, Aug 9, 2023 at 8:46=E2=80=AFPM Andrew Morton wrote: > > On Wed, 9 Aug 2023 18:46:33 +0200 Alexandre Ghiti wrote: > > > flush_cache_vmap() must be called after new vmalloc mappings are > > installed in the page table in order to allow architectures to make sur= e > > the new mapping is visible. > > Thanks. What are the user-visible effects of this bug? It could lead to a panic since on some architectures (like powerpc), the page table walker could see the wrong pte value and trigger a spurious page fault that can not be resolved (see commit f1cb8f9beba8 ("powerpc/64s/radix: avoid ptesync after set_pte and ptep_set_access_flags")). But actually the patch is aiming at riscv: the riscv specification allows the caching of invalid entries in the TLB, and since we recently removed the vmalloc page fault handling, we now need to emit a tlb shootdown whenever a new vmalloc mapping is emitted (https://lore.kernel.org/linux-riscv/20230725132246.817726-1-alexghiti@rivo= sinc.com/). That's a temporary solution, there are ways to avoid that :) Thanks, Alex