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Fri, 11 Oct 2024 19:16:13 -0700 (PDT) MIME-Version: 1.0 References: <20241010035048.3422527-1-maobibo@loongson.cn> <20241010035048.3422527-4-maobibo@loongson.cn> In-Reply-To: <20241010035048.3422527-4-maobibo@loongson.cn> From: Huacai Chen Date: Sat, 12 Oct 2024 10:16:01 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 3/4] LoongArch: Add barrier between set_pte and memory access To: Bibo Mao Cc: Andrey Ryabinin , Andrew Morton , David Hildenbrand , Barry Song , loongarch@lists.linux.dev, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: ismeq3gzx9azf65apaw4f3af4aqaqux3 X-Rspamd-Queue-Id: CF3C180006 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1728699369-177923 X-HE-Meta: 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 jnY/rBtS CW4oECATZLXIZeGdEdQZnyf3KwLCOjI5idfghxonguZJ9cWI7hBFbTdTlLpTJ8EpAhJidQqMJJj5iqE5i8+lynOYee5nohqIHLIvoVW36UbafpvNcCdNJaF4YzGiCOwo10XdJ1JJixzvgK5H/c+etahp2M5Ssy28rqhBVcV0tYG+e3R1cXFRNCnDDzu+JsKgp7xpUqkxfgFi4JquR6xrnLaTPZTBSAL9oaoQKs+F/UG5N2BPnbgWv9FmcIEIvjwxDCX0qAXqTbiM8vinUCk2W9QlsYOIXheah72c1CQWDIWi9Fw47fGaKuVYF9lKap2H5mKeqdvhbVzFys/+ScARSekCsAcrK5t0uid4P/FFfbcrzp7zqM2P8OYxgIcLmwGgdGSZzLc1ZkKeoEIYyo5HiGjb3hA== 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: Hi, Bibo, On Thu, Oct 10, 2024 at 11:50=E2=80=AFAM Bibo Mao wro= te: > > It is possible to return a spurious fault if memory is accessed > right after the pte is set. For user address space, pte is set > in kernel space and memory is accessed in user space, there is > long time for synchronization, no barrier needed. However for > kernel address space, it is possible that memory is accessed > right after the pte is set. > > Here flush_cache_vmap/flush_cache_vmap_early is used for > synchronization. > > Signed-off-by: Bibo Mao > --- > arch/loongarch/include/asm/cacheflush.h | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/arch/loongarch/include/asm/cacheflush.h b/arch/loongarch/inc= lude/asm/cacheflush.h > index f8754d08a31a..53be231319ef 100644 > --- a/arch/loongarch/include/asm/cacheflush.h > +++ b/arch/loongarch/include/asm/cacheflush.h > @@ -42,12 +42,24 @@ void local_flush_icache_range(unsigned long start, un= signed long end); > #define flush_cache_dup_mm(mm) do { } while (0) > #define flush_cache_range(vma, start, end) do { } while (0) > #define flush_cache_page(vma, vmaddr, pfn) do { } while (0) > -#define flush_cache_vmap(start, end) do { } while (0) > #define flush_cache_vunmap(start, end) do { } while (0) > #define flush_icache_user_page(vma, page, addr, len) do { } while (0) > #define flush_dcache_mmap_lock(mapping) do { } wh= ile (0) > #define flush_dcache_mmap_unlock(mapping) do { } while (0) > > +/* > + * It is possible for a kernel virtual mapping access to return a spurio= us > + * fault if it's accessed right after the pte is set. The page fault han= dler > + * does not expect this type of fault. flush_cache_vmap is not exactly t= he > + * right place to put this, but it seems to work well enough. > + */ > +static inline void flush_cache_vmap(unsigned long start, unsigned long e= nd) > +{ > + smp_mb(); > +} I don't know whether this is the best API to do this, and I think flush_cache_vunmap() also should be a smp_mb(). Huacai > +#define flush_cache_vmap flush_cache_vmap > +#define flush_cache_vmap_early flush_cache_vmap > + > #define cache_op(op, addr) \ > __asm__ __volatile__( \ > " cacop %0, %1 \n" \ > -- > 2.39.3 >