forked from Minki/linux
ec6347bb43
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 |
||
|---|---|---|
| .. | ||
| .gitignore | ||
| atomic64_32.c | ||
| atomic64_386_32.S | ||
| atomic64_cx8_32.S | ||
| cache-smp.c | ||
| checksum_32.S | ||
| clear_page_64.S | ||
| cmdline.c | ||
| cmpxchg8b_emu.S | ||
| cmpxchg16b_emu.S | ||
| copy_mc_64.S | ||
| copy_mc.c | ||
| copy_page_64.S | ||
| copy_user_64.S | ||
| cpu.c | ||
| csum-copy_64.S | ||
| csum-partial_64.c | ||
| csum-wrappers_64.c | ||
| delay.c | ||
| error-inject.c | ||
| getuser.S | ||
| hweight.S | ||
| inat.c | ||
| insn-eval.c | ||
| insn.c | ||
| iomap_copy_64.S | ||
| iomem.c | ||
| kaslr.c | ||
| Makefile | ||
| memcpy_32.c | ||
| memcpy_64.S | ||
| memmove_64.S | ||
| memset_64.S | ||
| misc.c | ||
| mmx_32.c | ||
| msr-reg-export.c | ||
| msr-reg.S | ||
| msr-smp.c | ||
| msr.c | ||
| putuser.S | ||
| retpoline.S | ||
| string_32.c | ||
| strstr_32.c | ||
| usercopy_32.c | ||
| usercopy_64.c | ||
| usercopy.c | ||
| x86-opcode-map.txt | ||