Messages in this thread | | | From | Nick Desaulniers <> | Date | Thu, 6 Oct 2022 10:56:47 -0700 | Subject | Re: [PATCH] x86/build: Move '-mindirect-branch-cs-prefix' out of GCC-only block |
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On Tue, Oct 4, 2022 at 2:27 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Thu, Aug 18, 2022 at 12:45 AM Peter Zijlstra <peterz@infradead.org> wrote: > > > > On Wed, Aug 17, 2022 at 03:08:01PM -0700, Nick Desaulniers wrote: > > > On Wed, Aug 17, 2022 at 11:56 AM Nathan Chancellor <nathan@kernel.org> wrote: > > > > > > > > LLVM 16 will have support for this flag so move it out of the GCC-only > > > > block to allow LLVM builds to take advantage of it. > > > > > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/1665 > > > > Link: https://github.com/llvm/llvm-project/commit/6f867f9102838ebe314c1f3661fdf95700386e5a > > > > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > > > > > > Thanks for the patch, I also boot tested this (in virtual guests for > > > both 64b and 32b). > > > > > > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > > > Tested-by: Nick Desaulniers <ndesaulniers@google.com> > > > > > > Peter, is there anything else special about these prefixes needed to > > > make use of them? > > > > The thing to do is boot with (warning, *very* verbose): > > > > "spectre_v2=retpoline,lfence debug-alternative" > > ah, debug-alternative also needs loglevel=8. Was wondering why I > wasn't getting anything new in the output... > > No kidding on the verbosity. For a defconfig, booting in QEMU and > redirecting stdout to a file produced a 95257 line file. > > $ grep "SMP alternatives: retpoline" /tmp/log.txt | wc -l > 18623 > $ du -h /tmp/log.txt > 11M /tmp/log.txt > $ grep "SMP alternatives: retpoline" /tmp/log.txt | tr -s ' ' > ... > [ 56.736261] SMP alternatives: retpoline at: > pm_check_save_msr+0x30/0x80 (ffffffffaa34b320) len: 6 to: > __x86_indirect_thunk_r11+0x0/0x20 > $ grep "SMP alternatives: retpoline" /tmp/log.txt | tr -s ' ' | cut -d > ' ' -f 10 | sort -u > 5 > 6 > # Curious about the 5, looks like there's only 2 cases: > $ grep "SMP alternatives: retpoline" /tmp/log.txt | grep 'len: 5' > [ 0.147261] SMP alternatives: retpoline at: ret_from_fork+0x1d/0x30 > (ffffffffa9601dbd) len: 5 to: __x86_indirect_thunk_rbx+0x0/0x20 > [ 2.274261] SMP alternatives: retpoline at: __efi_call+0x23/0x30 > (ffffffffa9671663) len: 5 to: __x86_indirect_thunk_rdi+0x0/0x20
For the typical len 6 case: [ 0.710345] SMP alternatives: ffffffffa2b6d1f2: orig: 2e e8 88 5f 09 ff [ 0.711345] SMP alternatives: ffffffffa2b6d1f2: repl: 0f ae e8 41 ff d3 [ 0.712345] SMP alternatives: retpoline at: setup_arch+0x4b0/0x58c (ffffffffa2b6d2ef) len: 6 to: __x86_indirect_thunk_r11+0x0/0x20
2e is the cs prefix, so it looks like this is working.
https://github.com/llvm/llvm-project/issues/58201 :^)
> Is there anything else I can do to help verify Nathan and Joao's > patches? If not, would you mind Ack'ing this so the x86 maintainers > can pick it up?
I see it's already been Acked, so NVM. This is good to go.
> Noting that Joao's patch was applied in my tests. > https://reviews.llvm.org/D134915 > I plan to land Joao's patch imminently.
Merging. -- Thanks, ~Nick Desaulniers
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