x86/clear_user: Make it faster
Based on a patch by Mark Hemment <markhemm@googlemail.com> 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. Drop the early clobbers from the @size and @addr operands as those are not needed anymore since we have single instruction alternatives. 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 <bp@suse.de> Link: https://lore.kernel.org/r/CAHk-=wh=Mu_EYhtOmPn6AxoQZyEh-4fo2Zx3G7rBv1g7vwoKiw@mail.gmail.com
This commit is contained in:
Borislav Petkov
Родитель
568035b01c
Коммит
0db7058e8e
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@ -502,9 +502,6 @@ strncpy_from_user(char *dst, const char __user *src, long count);
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extern __must_check long strnlen_user(const char __user *str, long n);
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unsigned long __must_check clear_user(void __user *mem, unsigned long len);
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unsigned long __must_check __clear_user(void __user *mem, unsigned long len);
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#ifdef CONFIG_ARCH_HAS_COPY_MC
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unsigned long __must_check
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copy_mc_to_kernel(void *to, const void *from, unsigned len);
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@ -526,6 +523,8 @@ extern struct movsl_mask {
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#define ARCH_HAS_NOCACHE_UACCESS 1
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#ifdef CONFIG_X86_32
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unsigned long __must_check clear_user(void __user *mem, unsigned long len);
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unsigned long __must_check __clear_user(void __user *mem, unsigned long len);
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# include <asm/uaccess_32.h>
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#else
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# include <asm/uaccess_64.h>
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@ -79,4 +79,49 @@ __copy_from_user_flushcache(void *dst, const void __user *src, unsigned size)
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kasan_check_write(dst, size);
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return __copy_user_flushcache(dst, src, size);
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}
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/*
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* Zero Userspace.
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*/
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__must_check unsigned long
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clear_user_original(void __user *addr, unsigned long len);
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__must_check unsigned long
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clear_user_rep_good(void __user *addr, unsigned long len);
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__must_check unsigned long
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clear_user_erms(void __user *addr, unsigned long len);
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static __always_inline __must_check unsigned long __clear_user(void __user *addr, unsigned long size)
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{
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might_fault();
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stac();
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/*
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* No memory constraint because it doesn't change any memory gcc
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* knows about.
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*/
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asm volatile(
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"1:\n\t"
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ALTERNATIVE_3("rep stosb",
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"call clear_user_erms", ALT_NOT(X86_FEATURE_FSRM),
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"call clear_user_rep_good", ALT_NOT(X86_FEATURE_ERMS),
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"call clear_user_original", ALT_NOT(X86_FEATURE_REP_GOOD))
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"2:\n"
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_ASM_EXTABLE_UA(1b, 2b)
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: "+c" (size), "+D" (addr), ASM_CALL_CONSTRAINT
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: "a" (0)
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/* rep_good clobbers %rdx */
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: "rdx");
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clac();
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return size;
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}
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static __always_inline unsigned long clear_user(void __user *to, unsigned long n)
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{
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if (access_ok(to, n))
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return __clear_user(to, n);
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return n;
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}
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#endif /* _ASM_X86_UACCESS_64_H */
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@ -1,5 +1,6 @@
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/* SPDX-License-Identifier: GPL-2.0-only */
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#include <linux/linkage.h>
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#include <asm/asm.h>
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#include <asm/export.h>
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/*
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@ -50,3 +51,140 @@ SYM_FUNC_START(clear_page_erms)
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RET
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SYM_FUNC_END(clear_page_erms)
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EXPORT_SYMBOL_GPL(clear_page_erms)
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/*
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* Default clear user-space.
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* Input:
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* rdi destination
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* rcx count
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*
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* Output:
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* rcx: uncleared bytes or 0 if successful.
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*/
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SYM_FUNC_START(clear_user_original)
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/*
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* Copy only the lower 32 bits of size as that is enough to handle the rest bytes,
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* i.e., no need for a 'q' suffix and thus a REX prefix.
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*/
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mov %ecx,%eax
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shr $3,%rcx
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jz .Lrest_bytes
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# do the qwords first
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.p2align 4
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.Lqwords:
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movq $0,(%rdi)
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lea 8(%rdi),%rdi
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dec %rcx
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jnz .Lqwords
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.Lrest_bytes:
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and $7, %eax
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jz .Lexit
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# now do the rest bytes
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.Lbytes:
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movb $0,(%rdi)
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inc %rdi
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dec %eax
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jnz .Lbytes
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.Lexit:
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/*
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* %rax still needs to be cleared in the exception case because this function is called
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* from inline asm and the compiler expects %rax to be zero when exiting the inline asm,
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* in case it might reuse it somewhere.
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*/
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xor %eax,%eax
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RET
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.Lqwords_exception:
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# convert remaining qwords back into bytes to return to caller
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shl $3, %rcx
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and $7, %eax
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add %rax,%rcx
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jmp .Lexit
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.Lbytes_exception:
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mov %eax,%ecx
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jmp .Lexit
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_ASM_EXTABLE_UA(.Lqwords, .Lqwords_exception)
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_ASM_EXTABLE_UA(.Lbytes, .Lbytes_exception)
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SYM_FUNC_END(clear_user_original)
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EXPORT_SYMBOL(clear_user_original)
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/*
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* Alternative clear user-space when CPU feature X86_FEATURE_REP_GOOD is
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* present.
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* Input:
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* rdi destination
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* rcx count
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*
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* Output:
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* rcx: uncleared bytes or 0 if successful.
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*/
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SYM_FUNC_START(clear_user_rep_good)
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# call the original thing for less than a cacheline
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cmp $64, %rcx
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jb clear_user_original
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.Lprep:
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# copy lower 32-bits for rest bytes
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mov %ecx, %edx
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shr $3, %rcx
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jz .Lrep_good_rest_bytes
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.Lrep_good_qwords:
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rep stosq
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.Lrep_good_rest_bytes:
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and $7, %edx
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jz .Lrep_good_exit
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.Lrep_good_bytes:
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mov %edx, %ecx
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rep stosb
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.Lrep_good_exit:
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# see .Lexit comment above
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xor %eax, %eax
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RET
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.Lrep_good_qwords_exception:
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# convert remaining qwords back into bytes to return to caller
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shl $3, %rcx
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and $7, %edx
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add %rdx, %rcx
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jmp .Lrep_good_exit
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_ASM_EXTABLE_UA(.Lrep_good_qwords, .Lrep_good_qwords_exception)
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_ASM_EXTABLE_UA(.Lrep_good_bytes, .Lrep_good_exit)
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SYM_FUNC_END(clear_user_rep_good)
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EXPORT_SYMBOL(clear_user_rep_good)
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/*
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* Alternative clear user-space when CPU feature X86_FEATURE_ERMS is present.
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* Input:
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* rdi destination
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* rcx count
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*
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* Output:
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* rcx: uncleared bytes or 0 if successful.
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*
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*/
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SYM_FUNC_START(clear_user_erms)
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# call the original thing for less than a cacheline
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cmp $64, %rcx
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jb clear_user_original
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.Lerms_bytes:
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rep stosb
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.Lerms_exit:
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xorl %eax,%eax
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RET
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_ASM_EXTABLE_UA(.Lerms_bytes, .Lerms_exit)
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SYM_FUNC_END(clear_user_erms)
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EXPORT_SYMBOL(clear_user_erms)
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@ -14,46 +14,6 @@
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* Zero Userspace
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*/
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unsigned long __clear_user(void __user *addr, unsigned long size)
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{
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long __d0;
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might_fault();
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/* no memory constraint because it doesn't change any memory gcc knows
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about */
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stac();
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asm volatile(
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" testq %[size8],%[size8]\n"
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" jz 4f\n"
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" .align 16\n"
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"0: movq $0,(%[dst])\n"
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" addq $8,%[dst]\n"
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" decl %%ecx ; jnz 0b\n"
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"4: movq %[size1],%%rcx\n"
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" testl %%ecx,%%ecx\n"
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" jz 2f\n"
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"1: movb $0,(%[dst])\n"
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" incq %[dst]\n"
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" decl %%ecx ; jnz 1b\n"
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"2:\n"
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_ASM_EXTABLE_TYPE_REG(0b, 2b, EX_TYPE_UCOPY_LEN8, %[size1])
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_ASM_EXTABLE_UA(1b, 2b)
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: [size8] "=&c"(size), [dst] "=&D" (__d0)
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: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr));
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clac();
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return size;
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}
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EXPORT_SYMBOL(__clear_user);
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unsigned long clear_user(void __user *to, unsigned long n)
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{
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if (access_ok(to, n))
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return __clear_user(to, n);
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return n;
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}
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EXPORT_SYMBOL(clear_user);
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#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
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/**
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* clean_cache_range - write back a cache range with CLWB
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@ -1071,6 +1071,9 @@ static const char *uaccess_safe_builtin[] = {
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"copy_mc_fragile_handle_tail",
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"copy_mc_enhanced_fast_string",
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"ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
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"clear_user_erms",
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"clear_user_rep_good",
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"clear_user_original",
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NULL
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};
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