From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 18B0A4A3C for ; Tue, 5 Jul 2022 17:01:20 +0000 (UTC) Received: from zn.tnic (p200300ea970ff682329c23fffea6a903.dip0.t-ipconnect.de [IPv6:2003:ea:970f:f682:329c:23ff:fea6:a903]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 1E4F81EC059E; Tue, 5 Jul 2022 19:01:10 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1657040470; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=wa6i1l9qsLGHrNkM+M0sFOa7ArDW/uI5veyzyHcmPv4=; b=dNsDofbnDuzYFn9qO04YhlDcMII11M8AM5p+6hawIJ1gYPqwtABVJujJ6Ok8uq7tdPX+2e 4R2kt/18Ha++R3zta+K2wA/d2Wey/x2v7B9cAEU1JKkBxqerixUrJKiArVkCm3h522HrLy 7NLA+CJb3P8hIVOto/ChUi7/iNyWcWU= Date: Tue, 5 Jul 2022 19:01:06 +0200 From: Borislav Petkov To: Linus Torvalds Cc: Mark Hemment , Andrew Morton , the arch/x86 maintainers , Peter Zijlstra , patrice.chotard@foss.st.com, Mikulas Patocka , Lukas Czerner , Christoph Hellwig , "Darrick J. Wong" , Chuck Lever , Hugh Dickins , patches@lists.linux.dev, Linux-MM , mm-commits@vger.kernel.org, Mel Gorman Subject: [PATCH -final] x86/clear_user: Make it faster Message-ID: References: Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Ok, here's the final version with the Intel findings added. I think I'm going to queue it - unless someone handwaves really loudly - because it is net code simplification, shows a good example how to inline insns instead of function calls - something which can be used for converting other primitives later - and the so called perf impact on Intel is only very minute because you can only see it in a microbenchmark. Oh, and it'll make CPU guys speed up their FSRM microcode. :-P Thx to all for the very helpful hints and ideas! --- From: Borislav Petkov Date: Tue, 24 May 2022 11:01:18 +0200 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Based on a patch by Mark Hemment and incorporating very sane suggestions from Linus. The point here is to have the default case with FSRM - which is supposed to be the majority of x86 hw out there - if not now then soon - be directly inlined into the instruction stream so that no function call overhead is taking place. The benchmarks I ran would show very small improvements and a PF benchmark would even show weird things like slowdowns with higher core counts. So for a ~6m running the git test suite, the function gets called under 700K times, all from padzero(): <...>-2536 [006] ..... 261.208801: padzero: to: 0x55b0663ed214, size: 3564, cycles: 21900 <...>-2536 [006] ..... 261.208819: padzero: to: 0x7f061adca078, size: 3976, cycles: 17160 <...>-2537 [008] ..... 261.211027: padzero: to: 0x5572d019e240, size: 3520, cycles: 23850 <...>-2537 [008] ..... 261.211049: padzero: to: 0x7f1288dc9078, size: 3976, cycles: 15900 ... which is around 1%-ish of the total time and which is consistent with the benchmark numbers. So Mel gave me the idea to simply measure how fast the function becomes. I.e.: start = rdtsc_ordered(); ret = __clear_user(to, n); end = rdtsc_ordered(); Computing the mean average of all the samples collected during the test suite run then shows some improvement: clear_user_original: Amean: 9219.71 (Sum: 6340154910, samples: 687674) fsrm: Amean: 8030.63 (Sum: 5522277720, samples: 687652) That's on Zen3. The situation looks a lot more confusing on Intel: Icelake: clear_user_original: Amean: 19679.4 (Sum: 13652560764, samples: 693750) Amean: 19743.7 (Sum: 13693470604, samples: 693562) (I ran it twice just to be sure.) ERMS: Amean: 20374.3 (Sum: 13910601024, samples: 682752) Amean: 20453.7 (Sum: 14186223606, samples: 693576) FSRM: Amean: 20458.2 (Sum: 13918381386, sample s: 680331) The original microbenchmark which people were complaining about: for i in $(seq 1 10); do dd if=/dev/zero of=/dev/null bs=1M status=progress count=65536; done 2>&1 | grep copied 32207011840 bytes (32 GB, 30 GiB) copied, 1 s, 32.2 GB/s 68719476736 bytes (69 GB, 64 GiB) copied, 1.93069 s, 35.6 GB/s 37597741056 bytes (38 GB, 35 GiB) copied, 1 s, 37.6 GB/s 68719476736 bytes (69 GB, 64 GiB) copied, 1.78017 s, 38.6 GB/s 62020124672 bytes (62 GB, 58 GiB) copied, 2 s, 31.0 GB/s 68719476736 bytes (69 GB, 64 GiB) copied, 2.13716 s, 32.2 GB/s 60010004480 bytes (60 GB, 56 GiB) copied, 1 s, 60.0 GB/s 68719476736 bytes (69 GB, 64 GiB) copied, 1.14129 s, 60.2 GB/s 53212086272 bytes (53 GB, 50 GiB) copied, 1 s, 53.2 GB/s 68719476736 bytes (69 GB, 64 GiB) copied, 1.28398 s, 53.5 GB/s 55698259968 bytes (56 GB, 52 GiB) copied, 1 s, 55.7 GB/s 68719476736 bytes (69 GB, 64 GiB) copied, 1.22507 s, 56.1 GB/s 55306092544 bytes (55 GB, 52 GiB) copied, 1 s, 55.3 GB/s 68719476736 bytes (69 GB, 64 GiB) copied, 1.23647 s, 55.6 GB/s 54387539968 bytes (54 GB, 51 GiB) copied, 1 s, 54.4 GB/s 68719476736 bytes (69 GB, 64 GiB) copied, 1.25693 s, 54.7 GB/s 50566529024 bytes (51 GB, 47 GiB) copied, 1 s, 50.6 GB/s 68719476736 bytes (69 GB, 64 GiB) copied, 1.35096 s, 50.9 GB/s 58308165632 bytes (58 GB, 54 GiB) copied, 1 s, 58.3 GB/s 68719476736 bytes (69 GB, 64 GiB) copied, 1.17394 s, 58.5 GB/s Now the same thing with smaller buffers: for i in $(seq 1 10); do dd if=/dev/zero of=/dev/null bs=1M status=progress count=8192; done 2>&1 | grep copied 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 0.28485 s, 30.2 GB/s 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 0.276112 s, 31.1 GB/s 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 0.29136 s, 29.5 GB/s 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 0.283803 s, 30.3 GB/s 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 0.306503 s, 28.0 GB/s 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 0.349169 s, 24.6 GB/s 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 0.276912 s, 31.0 GB/s 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 0.265356 s, 32.4 GB/s 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 0.28464 s, 30.2 GB/s 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 0.242998 s, 35.3 GB/s is also not conclusive because it all depends on the buffer sizes, their alignments and when the microcode detects that cachelines can be aggregated properly and copied in bigger sizes. Signed-off-by: Borislav Petkov Link: https://lore.kernel.org/r/CAHk-=wh=Mu_EYhtOmPn6AxoQZyEh-4fo2Zx3G7rBv1g7vwoKiw@mail.gmail.com --- arch/x86/include/asm/uaccess.h | 5 +- arch/x86/include/asm/uaccess_64.h | 45 ++++++++++ arch/x86/lib/clear_page_64.S | 138 ++++++++++++++++++++++++++++++ arch/x86/lib/usercopy_64.c | 40 --------- tools/objtool/check.c | 3 + 5 files changed, 188 insertions(+), 43 deletions(-) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 913e593a3b45..c46207946e05 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -502,9 +502,6 @@ strncpy_from_user(char *dst, const char __user *src, long count); extern __must_check long strnlen_user(const char __user *str, long n); -unsigned long __must_check clear_user(void __user *mem, unsigned long len); -unsigned long __must_check __clear_user(void __user *mem, unsigned long len); - #ifdef CONFIG_ARCH_HAS_COPY_MC unsigned long __must_check copy_mc_to_kernel(void *to, const void *from, unsigned len); @@ -526,6 +523,8 @@ extern struct movsl_mask { #define ARCH_HAS_NOCACHE_UACCESS 1 #ifdef CONFIG_X86_32 +unsigned long __must_check clear_user(void __user *mem, unsigned long len); +unsigned long __must_check __clear_user(void __user *mem, unsigned long len); # include #else # include diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h index 45697e04d771..4ffefb4bb844 100644 --- a/arch/x86/include/asm/uaccess_64.h +++ b/arch/x86/include/asm/uaccess_64.h @@ -79,4 +79,49 @@ __copy_from_user_flushcache(void *dst, const void __user *src, unsigned size) kasan_check_write(dst, size); return __copy_user_flushcache(dst, src, size); } + +/* + * Zero Userspace. + */ + +__must_check unsigned long +clear_user_original(void __user *addr, unsigned long len); +__must_check unsigned long +clear_user_rep_good(void __user *addr, unsigned long len); +__must_check unsigned long +clear_user_erms(void __user *addr, unsigned long len); + +static __always_inline __must_check unsigned long __clear_user(void __user *addr, unsigned long size) +{ + might_fault(); + stac(); + + /* + * No memory constraint because it doesn't change any memory gcc + * knows about. + */ + asm volatile( + "1:\n\t" + ALTERNATIVE_3("rep stosb", + "call clear_user_erms", ALT_NOT(X86_FEATURE_FSRM), + "call clear_user_rep_good", ALT_NOT(X86_FEATURE_ERMS), + "call clear_user_original", ALT_NOT(X86_FEATURE_REP_GOOD)) + "2:\n" + _ASM_EXTABLE_UA(1b, 2b) + : "+&c" (size), "+&D" (addr), ASM_CALL_CONSTRAINT + : "a" (0) + /* rep_good clobbers %rdx */ + : "rdx"); + + clac(); + + return size; +} + +static __always_inline unsigned long clear_user(void __user *to, unsigned long n) +{ + if (access_ok(to, n)) + return __clear_user(to, n); + return n; +} #endif /* _ASM_X86_UACCESS_64_H */ diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S index fe59b8ac4fcc..ecbfb4dd3b01 100644 --- a/arch/x86/lib/clear_page_64.S +++ b/arch/x86/lib/clear_page_64.S @@ -1,5 +1,6 @@ /* SPDX-License-Identifier: GPL-2.0-only */ #include +#include #include /* @@ -50,3 +51,140 @@ SYM_FUNC_START(clear_page_erms) RET SYM_FUNC_END(clear_page_erms) EXPORT_SYMBOL_GPL(clear_page_erms) + +/* + * Default clear user-space. + * Input: + * rdi destination + * rcx count + * + * Output: + * rcx: uncleared bytes or 0 if successful. + */ +SYM_FUNC_START(clear_user_original) + /* + * Copy only the lower 32 bits of size as that is enough to handle the rest bytes, + * i.e., no need for a 'q' suffix and thus a REX prefix. + */ + mov %ecx,%eax + shr $3,%rcx + jz .Lrest_bytes + + # do the qwords first + .p2align 4 +.Lqwords: + movq $0,(%rdi) + lea 8(%rdi),%rdi + dec %rcx + jnz .Lqwords + +.Lrest_bytes: + and $7, %eax + jz .Lexit + + # now do the rest bytes +.Lbytes: + movb $0,(%rdi) + inc %rdi + dec %eax + jnz .Lbytes + +.Lexit: + /* + * %rax still needs to be cleared in the exception case because this function is called + * from inline asm and the compiler expects %rax to be zero when exiting the inline asm, + * in case it might reuse it somewhere. + */ + xor %eax,%eax + RET + +.Lqwords_exception: + # convert remaining qwords back into bytes to return to caller + shl $3, %rcx + and $7, %eax + add %rax,%rcx + jmp .Lexit + +.Lbytes_exception: + mov %eax,%ecx + jmp .Lexit + + _ASM_EXTABLE_UA(.Lqwords, .Lqwords_exception) + _ASM_EXTABLE_UA(.Lbytes, .Lbytes_exception) +SYM_FUNC_END(clear_user_original) +EXPORT_SYMBOL(clear_user_original) + +/* + * Alternative clear user-space when CPU feature X86_FEATURE_REP_GOOD is + * present. + * Input: + * rdi destination + * rcx count + * + * Output: + * rcx: uncleared bytes or 0 if successful. + */ +SYM_FUNC_START(clear_user_rep_good) + # call the original thing for less than a cacheline + cmp $64, %rcx + jb clear_user_original + +.Lprep: + # copy lower 32-bits for rest bytes + mov %ecx, %edx + shr $3, %rcx + jz .Lrep_good_rest_bytes + +.Lrep_good_qwords: + rep stosq + +.Lrep_good_rest_bytes: + and $7, %edx + jz .Lrep_good_exit + +.Lrep_good_bytes: + mov %edx, %ecx + rep stosb + +.Lrep_good_exit: + # see .Lexit comment above + xor %eax, %eax + RET + +.Lrep_good_qwords_exception: + # convert remaining qwords back into bytes to return to caller + shl $3, %rcx + and $7, %edx + add %rdx, %rcx + jmp .Lrep_good_exit + + _ASM_EXTABLE_UA(.Lrep_good_qwords, .Lrep_good_qwords_exception) + _ASM_EXTABLE_UA(.Lrep_good_bytes, .Lrep_good_exit) +SYM_FUNC_END(clear_user_rep_good) +EXPORT_SYMBOL(clear_user_rep_good) + +/* + * Alternative clear user-space when CPU feature X86_FEATURE_ERMS is present. + * Input: + * rdi destination + * rcx count + * + * Output: + * rcx: uncleared bytes or 0 if successful. + * + */ +SYM_FUNC_START(clear_user_erms) + # call the original thing for less than a cacheline + cmp $64, %rcx + jb clear_user_original + +.Lerms_bytes: + rep stosb + +.Lerms_exit: + xorl %eax,%eax + RET + + _ASM_EXTABLE_UA(.Lerms_bytes, .Lerms_exit) +SYM_FUNC_END(clear_user_erms) +EXPORT_SYMBOL(clear_user_erms) diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c index 0ae6cf804197..6c1f8ac5e721 100644 --- a/arch/x86/lib/usercopy_64.c +++ b/arch/x86/lib/usercopy_64.c @@ -14,46 +14,6 @@ * Zero Userspace */ -unsigned long __clear_user(void __user *addr, unsigned long size) -{ - long __d0; - might_fault(); - /* no memory constraint because it doesn't change any memory gcc knows - about */ - stac(); - asm volatile( - " testq %[size8],%[size8]\n" - " jz 4f\n" - " .align 16\n" - "0: movq $0,(%[dst])\n" - " addq $8,%[dst]\n" - " decl %%ecx ; jnz 0b\n" - "4: movq %[size1],%%rcx\n" - " testl %%ecx,%%ecx\n" - " jz 2f\n" - "1: movb $0,(%[dst])\n" - " incq %[dst]\n" - " decl %%ecx ; jnz 1b\n" - "2:\n" - - _ASM_EXTABLE_TYPE_REG(0b, 2b, EX_TYPE_UCOPY_LEN8, %[size1]) - _ASM_EXTABLE_UA(1b, 2b) - - : [size8] "=&c"(size), [dst] "=&D" (__d0) - : [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr)); - clac(); - return size; -} -EXPORT_SYMBOL(__clear_user); - -unsigned long clear_user(void __user *to, unsigned long n) -{ - if (access_ok(to, n)) - return __clear_user(to, n); - return n; -} -EXPORT_SYMBOL(clear_user); - #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE /** * clean_cache_range - write back a cache range with CLWB diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 864bb9dd3584..98598f3c74c3 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1024,6 +1024,9 @@ static const char *uaccess_safe_builtin[] = { "copy_mc_fragile_handle_tail", "copy_mc_enhanced_fast_string", "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */ + "clear_user_erms", + "clear_user_rep_good", + "clear_user_original", NULL }; -- 2.35.1 -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette