From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [PATCH v3 18/26] arm64: Introduce asm/vdso/processor.h Date: Mon, 16 Mar 2020 11:22:06 +0000 Message-ID: <20200316112205.GE3005@mbp> References: <20200313154345.56760-1-vincenzo.frascino@arm.com> <20200313154345.56760-19-vincenzo.frascino@arm.com> <20200315182950.GB32205@mbp> <20200316103437.GD3005@mbp> <77a2e91a-58f4-3ba3-9eef-42d6a8faf859@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from foss.arm.com ([217.140.110.172]:46470 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730734AbgCPLWM (ORCPT ); Mon, 16 Mar 2020 07:22:12 -0400 Content-Disposition: inline In-Reply-To: <77a2e91a-58f4-3ba3-9eef-42d6a8faf859@arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Vincenzo Frascino Cc: linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, clang-built-linux@googlegroups.com, x86@kernel.org, Will Deacon , Arnd Bergmann , Russell King , Paul Burton , Thomas Gleixner , Andy Lutomirski , Ingo Molnar , Borislav Petkov , Stephen Boyd , Mark Salyzyn , Kees Cook , Peter Collingbourne , Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Nick Desaulniers , Marc Zyngier Mark On Mon, Mar 16, 2020 at 10:55:00AM +0000, Vincenzo Frascino wrote: > On 3/16/20 10:34 AM, Catalin Marinas wrote: > >> I tried to fine grain the headers as much as I could in order to avoid > >> unneeded/unwanted inclusions: > >> * TASK_SIZE_32 is used to verify ABI consistency on vdso32 (please refer to > >> arch/arm64/kernel/vdso32/vgettimeofday.c). > > > > I see. But the test is probably useless. With 4K pages, TASK_SIZE_32 is > > 1UL << 32, so you can't have a u32 greater than this. So I'd argue that > > the ABI compatibility here doesn't matter. > > > > With 16K or 64K pages, TASK_SIZE_32 is slightly smaller but arm32 never > > supported it. > > > > What's the side-effect of dropping this check altogether? > > The main side-effect is that arm32 and arm64 compat have a different behavior, > that it is what we want to avoid. > > The vdsotest [1] I am using, verifies all the side conditions with respect to > the ABI, which we are now compatible with. Removing those checks would break > this condition. As I said above, I don't see how removing 'if ((u32)ts >= (1UL << 32))' makes any difference. This check was likely removed by the compiler already. Also, userspace doesn't have a trivial way to figure out TASK_SIZE and I can't see anything that tests this in the vdsotest (though I haven't spent that much time looking). If it's hard-coded, note that arm32 TASK_SIZE is different from TASK_SIZE_32 on arm64. Can you tell what actually is failing in vdsotest if you remove the TASK_SIZE_32 checks in the arm64 compat vdso? -- Catalin From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.110.172]:46470 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730734AbgCPLWM (ORCPT ); Mon, 16 Mar 2020 07:22:12 -0400 Date: Mon, 16 Mar 2020 11:22:06 +0000 From: Catalin Marinas Subject: Re: [PATCH v3 18/26] arm64: Introduce asm/vdso/processor.h Message-ID: <20200316112205.GE3005@mbp> References: <20200313154345.56760-1-vincenzo.frascino@arm.com> <20200313154345.56760-19-vincenzo.frascino@arm.com> <20200315182950.GB32205@mbp> <20200316103437.GD3005@mbp> <77a2e91a-58f4-3ba3-9eef-42d6a8faf859@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <77a2e91a-58f4-3ba3-9eef-42d6a8faf859@arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Vincenzo Frascino Cc: linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, clang-built-linux@googlegroups.com, x86@kernel.org, Will Deacon , Arnd Bergmann , Russell King , Paul Burton , Thomas Gleixner , Andy Lutomirski , Ingo Molnar , Borislav Petkov , Stephen Boyd , Mark Salyzyn , Kees Cook , Peter Collingbourne , Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Nick Desaulniers , Marc Zyngier , Mark Rutland , Will Deacon Message-ID: <20200316112206.aJKsYz7c9BRrH5Tt9MXGTkoX_IC9bq6sob-QeVLx_64@z> On Mon, Mar 16, 2020 at 10:55:00AM +0000, Vincenzo Frascino wrote: > On 3/16/20 10:34 AM, Catalin Marinas wrote: > >> I tried to fine grain the headers as much as I could in order to avoid > >> unneeded/unwanted inclusions: > >> * TASK_SIZE_32 is used to verify ABI consistency on vdso32 (please refer to > >> arch/arm64/kernel/vdso32/vgettimeofday.c). > > > > I see. But the test is probably useless. With 4K pages, TASK_SIZE_32 is > > 1UL << 32, so you can't have a u32 greater than this. So I'd argue that > > the ABI compatibility here doesn't matter. > > > > With 16K or 64K pages, TASK_SIZE_32 is slightly smaller but arm32 never > > supported it. > > > > What's the side-effect of dropping this check altogether? > > The main side-effect is that arm32 and arm64 compat have a different behavior, > that it is what we want to avoid. > > The vdsotest [1] I am using, verifies all the side conditions with respect to > the ABI, which we are now compatible with. Removing those checks would break > this condition. As I said above, I don't see how removing 'if ((u32)ts >= (1UL << 32))' makes any difference. This check was likely removed by the compiler already. Also, userspace doesn't have a trivial way to figure out TASK_SIZE and I can't see anything that tests this in the vdsotest (though I haven't spent that much time looking). If it's hard-coded, note that arm32 TASK_SIZE is different from TASK_SIZE_32 on arm64. Can you tell what actually is failing in vdsotest if you remove the TASK_SIZE_32 checks in the arm64 compat vdso? -- Catalin