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[109.64.41.91]) by smtp.gmail.com with ESMTPSA id u3sm2642917wrw.89.2020.06.02.01.45.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Jun 2020 01:45:07 -0700 (PDT) Date: Tue, 2 Jun 2020 04:45:05 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Jason Wang , netdev@vger.kernel.org Subject: [PATCH RFC] uaccess: user_access_begin_after_access_ok() Message-ID: <20200602084257.134555-1-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Mailer: git-send-email 2.24.1.751.gd10ce2899c X-Mutt-Fcc: =sent Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org So vhost needs to poke at userspace *a lot* in a quick succession. It is thus benefitial to enable userspace access, do our thing, then disable. Except access_ok has already been pre-validated with all the relevant nospec checks, so we don't need that. Add an API to allow userspace access after access_ok and barrier_nospec are done. Signed-off-by: Michael S. Tsirkin --- Jason, so I've been thinking using something along these lines, then switching vhost to use unsafe_copy_to_user and friends would solve lots of problems you observed with SMAP. What do you think? Do we need any other APIs to make it practical? arch/x86/include/asm/uaccess.h | 1 + include/linux/uaccess.h | 1 + 2 files changed, 2 insertions(+) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index d8f283b9a569..fa5afb3a54fe 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -483,6 +483,7 @@ static __must_check __always_inline bool user_access_begin(const void __user *pt return 1; } #define user_access_begin(a,b) user_access_begin(a,b) +#define user_access_begin_after_access_ok() __uaccess_begin() #define user_access_end() __uaccess_end() #define user_access_save() smap_save() diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 67f016010aad..4c0a959ad639 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -370,6 +370,7 @@ extern long strnlen_unsafe_user(const void __user *unsafe_addr, long count); #ifndef user_access_begin #define user_access_begin(ptr,len) access_ok(ptr, len) +#define user_access_begin_after_access_ok() do { } while (0) #define user_access_end() do { } while (0) #define unsafe_op_wrap(op, err) do { if (unlikely(op)) goto err; } while (0) #define unsafe_get_user(x,p,e) unsafe_op_wrap(__get_user(x,p),e) -- MST