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In reaction to a proposal to introduce a memcpy_mcsafe_fast() implementation Linus points out that memcpy_mcsafe() is poorly named relative to communicating the scope of the interface. Specifically what addresses are valid to pass as source, destination, and what faults / exceptions are handled. Of particular concern is that even though x86 might be able to handle the semantics of copy_mc_to_user() with its common copy_user_generic() implementation other archs likely need / want an explicit path for this case: On Fri, May 1, 2020 at 11:28 AM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > On Thu, Apr 30, 2020 at 6:21 PM Dan Williams <dan.j.williams@intel.com> wrote: > > > > However now I see that copy_user_generic() works for the wrong reason. > > It works because the exception on the source address due to poison > > looks no different than a write fault on the user address to the > > caller, it's still just a short copy. So it makes copy_to_user() work > > for the wrong reason relative to the name. > > Right. > > And it won't work that way on other architectures. On x86, we have a > generic function that can take faults on either side, and we use it > for both cases (and for the "in_user" case too), but that's an > artifact of the architecture oddity. > > In fact, it's probably wrong even on x86 - because it can hide bugs - > but writing those things is painful enough that everybody prefers > having just one function. Replace a single top-level memcpy_mcsafe() with either copy_mc_to_user(), or copy_mc_to_kernel(). Introduce an x86 copy_mc_fragile() name as the rename for the low-level x86 implementation formerly named memcpy_mcsafe(). It is used as the slow / careful backend that is supplanted by a fast copy_mc_generic() in a follow-on patch. One side-effect of this reorganization is that separating copy_mc_64.S to its own file means that perf no longer needs to track dependencies for its memcpy_64.S benchmarks. [ bp: Massage a bit. ] Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Tony Luck <tony.luck@intel.com> Acked-by: Michael Ellerman <mpe@ellerman.id.au> Cc: <stable@vger.kernel.org> Link: http://lore.kernel.org/r/CAHk-=wjSqtXAqfUJxFtWNwmguFASTgB0dz1dT3V-78Quiezqbg@mail.gmail.com Link: https://lkml.kernel.org/r/160195561680.2163339.11574962055305783722.stgit@dwillia2-desk3.amr.corp.intel.com
75 lines
1.4 KiB
C
75 lines
1.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _COPY_MC_TEST_H_
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#define _COPY_MC_TEST_H_
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#ifndef __ASSEMBLY__
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#ifdef CONFIG_COPY_MC_TEST
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extern unsigned long copy_mc_test_src;
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extern unsigned long copy_mc_test_dst;
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static inline void copy_mc_inject_src(void *addr)
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{
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if (addr)
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copy_mc_test_src = (unsigned long) addr;
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else
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copy_mc_test_src = ~0UL;
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}
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static inline void copy_mc_inject_dst(void *addr)
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{
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if (addr)
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copy_mc_test_dst = (unsigned long) addr;
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else
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copy_mc_test_dst = ~0UL;
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}
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#else /* CONFIG_COPY_MC_TEST */
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static inline void copy_mc_inject_src(void *addr)
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{
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}
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static inline void copy_mc_inject_dst(void *addr)
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{
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}
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#endif /* CONFIG_COPY_MC_TEST */
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#else /* __ASSEMBLY__ */
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#include <asm/export.h>
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#ifdef CONFIG_COPY_MC_TEST
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.macro COPY_MC_TEST_CTL
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.pushsection .data
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.align 8
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.globl copy_mc_test_src
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copy_mc_test_src:
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.quad 0
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EXPORT_SYMBOL_GPL(copy_mc_test_src)
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.globl copy_mc_test_dst
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copy_mc_test_dst:
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.quad 0
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EXPORT_SYMBOL_GPL(copy_mc_test_dst)
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.popsection
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.endm
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.macro COPY_MC_TEST_SRC reg count target
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leaq \count(\reg), %r9
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cmp copy_mc_test_src, %r9
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ja \target
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.endm
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.macro COPY_MC_TEST_DST reg count target
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leaq \count(\reg), %r9
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cmp copy_mc_test_dst, %r9
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ja \target
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.endm
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#else
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.macro COPY_MC_TEST_CTL
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.endm
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.macro COPY_MC_TEST_SRC reg count target
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.endm
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.macro COPY_MC_TEST_DST reg count target
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.endm
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#endif /* CONFIG_COPY_MC_TEST */
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#endif /* __ASSEMBLY__ */
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#endif /* _COPY_MC_TEST_H_ */
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