diff options
author | Dan Williams <dan.j.williams@intel.com> | 2020-10-05 20:40:16 -0700 |
---|---|---|
committer | Borislav Petkov <bp@suse.de> | 2020-10-06 11:18:04 +0200 |
commit | ec6347bb43395cb92126788a1a5b25302543f815 (patch) | |
tree | 98a65bc27c57de7d21fdf657e0e94a95bb50935f /arch/x86/lib/copy_mc.c | |
parent | ed9705e4ad1c19ae51ed0cb4c112f9eb6dfc69fc (diff) |
x86, powerpc: Rename memcpy_mcsafe() to copy_mc_to_{user, kernel}()
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
Diffstat (limited to 'arch/x86/lib/copy_mc.c')
-rw-r--r-- | arch/x86/lib/copy_mc.c | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/arch/x86/lib/copy_mc.c b/arch/x86/lib/copy_mc.c new file mode 100644 index 000000000000..2633635530b7 --- /dev/null +++ b/arch/x86/lib/copy_mc.c @@ -0,0 +1,82 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright(c) 2016-2020 Intel Corporation. All rights reserved. */ + +#include <linux/jump_label.h> +#include <linux/uaccess.h> +#include <linux/export.h> +#include <linux/string.h> +#include <linux/types.h> + +#include <asm/mce.h> + +#ifdef CONFIG_X86_MCE +/* + * See COPY_MC_TEST for self-test of the copy_mc_fragile() + * implementation. + */ +static DEFINE_STATIC_KEY_FALSE(copy_mc_fragile_key); + +void enable_copy_mc_fragile(void) +{ + static_branch_inc(©_mc_fragile_key); +} +#define copy_mc_fragile_enabled (static_branch_unlikely(©_mc_fragile_key)) + +/* + * Similar to copy_user_handle_tail, probe for the write fault point, or + * source exception point. + */ +__visible notrace unsigned long +copy_mc_fragile_handle_tail(char *to, char *from, unsigned len) +{ + for (; len; --len, to++, from++) + if (copy_mc_fragile(to, from, 1)) + break; + return len; +} +#else +/* + * No point in doing careful copying, or consulting a static key when + * there is no #MC handler in the CONFIG_X86_MCE=n case. + */ +void enable_copy_mc_fragile(void) +{ +} +#define copy_mc_fragile_enabled (0) +#endif + +/** + * copy_mc_to_kernel - memory copy that handles source exceptions + * + * @dst: destination address + * @src: source address + * @len: number of bytes to copy + * + * Call into the 'fragile' version on systems that have trouble + * actually do machine check recovery. Everyone else can just + * use memcpy(). + * + * Return 0 for success, or number of bytes not copied if there was an + * exception. + */ +unsigned long __must_check copy_mc_to_kernel(void *dst, const void *src, unsigned len) +{ + if (copy_mc_fragile_enabled) + return copy_mc_fragile(dst, src, len); + memcpy(dst, src, len); + return 0; +} +EXPORT_SYMBOL_GPL(copy_mc_to_kernel); + +unsigned long __must_check copy_mc_to_user(void *dst, const void *src, unsigned len) +{ + unsigned long ret; + + if (!copy_mc_fragile_enabled) + return copy_user_generic(dst, src, len); + + __uaccess_begin(); + ret = copy_mc_fragile(dst, src, len); + __uaccess_end(); + return ret; +} |