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 15:49:31 +0000 Message-ID: <20200316154930.GG3005@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> <20200316112205.GE3005@mbp> <9a0a9285-8a45-4f65-3a83-813cabd0f0d3@arm.com> <20200316144346.GF3005@mbp> <427064ee-45df-233c-0281-69e3d62ba784@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <427064ee-45df-233c-0281-69e3d62ba784@arm.com> Sender: linux-mips-owner@vger.kernel.org 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 List-Id: linux-arch.vger.kernel.org On Mon, Mar 16, 2020 at 03:33:30PM +0000, Vincenzo Frascino wrote: > On 3/16/20 2:43 PM, Catalin Marinas wrote[...] > >> To me does not seem optimized out. Which version of the compiler are you using? > > > > I misread the #ifdef'ery in asm/processor.h. So with 4K pages, > > TASK_SIZE_32 is (1UL<<32)-PAGE_SIZE. However, with 64K pages _and_ > > CONFIG_KUSER_HELPERS, TASK_SIZE_32 is 1UL<<32 and the check is removed > > by the compiler. > > > > With the 4K build, __vdso_clock_gettime starts as: > > > > 00000194 <__vdso_clock_gettime>: > > 194: f511 5f80 cmn.w r1, #4096 ; 0x1000 > > 198: d214 bcs.n 1c4 <__vdso_clock_gettime+0x30> > > 19a: b5b0 push {r4, r5, r7, lr} > > ... > > 1c4: f06f 000d mvn.w r0, #13 > > 1c8: 4770 bx lr > > > > With 64K pages: > > > > 00000194 <__vdso_clock_gettime>: > > 194: b5b0 push {r4, r5, r7, lr} > > ... > > 1be: bdb0 pop {r4, r5, r7, pc} > > > > I haven't tried but it's likely that the vdsotest fails with 64K pages > > and compat enabled (requires EXPERT). > > This makes more sense. Thanks for the clarification. > > I agree on the behavior of 64K pages and I think as well that the > "compatibility" issue is still there. However as you correctly stated in your > first email arm32 never supported 16K or 64K pages, hence I think we should not > be concerned about compatibility in this cases. My point is that even with 4K pages it's not really compatibility. The test uses UINTPTR_MAX but on arm32 it would also fail with 0xc0000000. On arm64 compat, however, this value would pass just fine. > To make it more explicit we could make COMPAT_VDSO on arm64 depend on > ARM64_4K_PAGES. What do you think? No, I don't see why we should add this limitation. > >> Please find below the list of errors for clock_gettime (similar for the other): > >> > >> passing UINTPTR_MAX to clock_gettime (VDSO): terminated by unexpected signal 7 > >> clock-gettime-monotonic/abi: 1 failures/inconsistencies encountered > > > > Ah, so it uses UINTPTR_MAX in the test. Fair enough but I don't think > > the arm64 check is entirely useful. On arm32, the check was meant to > > return -EFAULT for addresses beyond TASK_SIZE that may enter into the > > kernel or module space. On arm64 compat, the kernel space is well above > > the reach of the 32-bit code. > > > > If you want to preserve some compatibility for this specific test, what > > about checking for wrapping around 0, I think it would make more sense. > > Something like: > > > > if ((u32)ts > UINTPTR_MAX - sizeof(*ts) + 1) > > Ok, sounds good to me. But it is something that this patch series inherited, > hence I would prefer to send a separate patch that introduces what you are > proposing and removes TASK_SIZE_32 from the headers. How does it sound? I'd rather avoid moving TASK_SIZE_32 unnecessarily. Just add a preparatory patch to your series for arm64 compat vdso and follow with the rest without moving TASK_SIZE_32 around. -- Catalin From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.110.172]:51048 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731924AbgCPPtp (ORCPT ); Mon, 16 Mar 2020 11:49:45 -0400 Date: Mon, 16 Mar 2020 15:49:31 +0000 From: Catalin Marinas Subject: Re: [PATCH v3 18/26] arm64: Introduce asm/vdso/processor.h Message-ID: <20200316154930.GG3005@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> <20200316112205.GE3005@mbp> <9a0a9285-8a45-4f65-3a83-813cabd0f0d3@arm.com> <20200316144346.GF3005@mbp> <427064ee-45df-233c-0281-69e3d62ba784@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <427064ee-45df-233c-0281-69e3d62ba784@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: <20200316154931.uNhfEHGgCqfEuVysaWWrkl3xJkVOJ68oghkllyut3Ww@z> On Mon, Mar 16, 2020 at 03:33:30PM +0000, Vincenzo Frascino wrote: > On 3/16/20 2:43 PM, Catalin Marinas wrote[...] > >> To me does not seem optimized out. Which version of the compiler are you using? > > > > I misread the #ifdef'ery in asm/processor.h. So with 4K pages, > > TASK_SIZE_32 is (1UL<<32)-PAGE_SIZE. However, with 64K pages _and_ > > CONFIG_KUSER_HELPERS, TASK_SIZE_32 is 1UL<<32 and the check is removed > > by the compiler. > > > > With the 4K build, __vdso_clock_gettime starts as: > > > > 00000194 <__vdso_clock_gettime>: > > 194: f511 5f80 cmn.w r1, #4096 ; 0x1000 > > 198: d214 bcs.n 1c4 <__vdso_clock_gettime+0x30> > > 19a: b5b0 push {r4, r5, r7, lr} > > ... > > 1c4: f06f 000d mvn.w r0, #13 > > 1c8: 4770 bx lr > > > > With 64K pages: > > > > 00000194 <__vdso_clock_gettime>: > > 194: b5b0 push {r4, r5, r7, lr} > > ... > > 1be: bdb0 pop {r4, r5, r7, pc} > > > > I haven't tried but it's likely that the vdsotest fails with 64K pages > > and compat enabled (requires EXPERT). > > This makes more sense. Thanks for the clarification. > > I agree on the behavior of 64K pages and I think as well that the > "compatibility" issue is still there. However as you correctly stated in your > first email arm32 never supported 16K or 64K pages, hence I think we should not > be concerned about compatibility in this cases. My point is that even with 4K pages it's not really compatibility. The test uses UINTPTR_MAX but on arm32 it would also fail with 0xc0000000. On arm64 compat, however, this value would pass just fine. > To make it more explicit we could make COMPAT_VDSO on arm64 depend on > ARM64_4K_PAGES. What do you think? No, I don't see why we should add this limitation. > >> Please find below the list of errors for clock_gettime (similar for the other): > >> > >> passing UINTPTR_MAX to clock_gettime (VDSO): terminated by unexpected signal 7 > >> clock-gettime-monotonic/abi: 1 failures/inconsistencies encountered > > > > Ah, so it uses UINTPTR_MAX in the test. Fair enough but I don't think > > the arm64 check is entirely useful. On arm32, the check was meant to > > return -EFAULT for addresses beyond TASK_SIZE that may enter into the > > kernel or module space. On arm64 compat, the kernel space is well above > > the reach of the 32-bit code. > > > > If you want to preserve some compatibility for this specific test, what > > about checking for wrapping around 0, I think it would make more sense. > > Something like: > > > > if ((u32)ts > UINTPTR_MAX - sizeof(*ts) + 1) > > Ok, sounds good to me. But it is something that this patch series inherited, > hence I would prefer to send a separate patch that introduces what you are > proposing and removes TASK_SIZE_32 from the headers. How does it sound? I'd rather avoid moving TASK_SIZE_32 unnecessarily. Just add a preparatory patch to your series for arm64 compat vdso and follow with the rest without moving TASK_SIZE_32 around. -- Catalin