From: Peter Zijlstra <peterz@infradead.org>
To: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com,
konrad.wilk@oracle.com, x86@kernel.org, dwmw@amazon.co.uk,
tglx@linutronix.de,
Srinivas REDDY Eeda <srinivas.eeda@oracle.com>,
bp@suse.de, hpa@zytor.com, dhaval.giani@oracle.com
Subject: Re: [PATCH] x86/speculation: Use AMD specific retpoline for inline asm on AMD
Date: Tue, 18 Sep 2018 11:50:15 +0200 [thread overview]
Message-ID: <20180918095015.GE19234@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <87411705-893f-46d3-b899-b09ed9fa8d1b@default>
On Mon, Sep 17, 2018 at 10:17:30PM -0700, Zhenzhong Duan wrote:
> Lfence is preferred than general retpoline on AMD, add this option
> in C / inline asm just as the ASM code does.
>
> For x86_64, it still help to have minimal retpoline for kernel even
> if gcc doesn't support it, change the inline asm for x86 so that it
> could also be used by x86_64.
> Add ANNOTATE_NOSPEC_ALTERNATIVE for i386 to avoid below warning:
> "warning: objtool: .altinstr_replacement+0x10: unsupported
> intra-function call"
> "warning: objtool: If this is a retpoline, please patch it
> in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE."
This Changelog is almost unreadable, please rewrite.
Reverse engineering the patch you add RETPOLINE_AMD support to the
inline-asm CALL_NOSPEC so that they match the asm CALL_NOSPEC.
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> ---
> arch/x86/include/asm/nospec-branch.h | 23 ++++++++++++++++-------
> 1 files changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
> index fd2a8c1..2d49eab 100644
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -170,21 +170,26 @@
> */
> # define CALL_NOSPEC \
> ANNOTATE_NOSPEC_ALTERNATIVE \
> - ALTERNATIVE( \
> + ALTERNATIVE_2( \
> ANNOTATE_RETPOLINE_SAFE \
> "call *%[thunk_target]\n", \
> "call __x86_indirect_thunk_%V[thunk_target]\n", \
> - X86_FEATURE_RETPOLINE)
> + X86_FEATURE_RETPOLINE, \
> + "lfence;\n" \
> + ANNOTATE_RETPOLINE_SAFE \
> + "call *%[thunk_target]\n", \
> + X86_FEATURE_RETPOLINE_AMD)
> # define THUNK_TARGET(addr) [thunk_target] "r" (addr)
That's OK.
>
> -#elif defined(CONFIG_X86_32) && defined(CONFIG_RETPOLINE)
> +#elif defined(CONFIG_RETPOLINE)
This doesn't make any sense..
> /*
> * For i386 we use the original ret-equivalent retpoline, because
> * otherwise we'll run out of registers. We don't care about CET
> * here, anyway.
> */
> # define CALL_NOSPEC \
> - ALTERNATIVE( \
> + ANNOTATE_NOSPEC_ALTERNATIVE \
> + ALTERNATIVE_2( \
> ANNOTATE_RETPOLINE_SAFE \
> "call *%[thunk_target]\n", \
> " jmp 904f;\n" \
> @@ -194,12 +199,16 @@
> " lfence;\n" \
> " jmp 902b;\n" \
> " .align 16\n" \
> - "903: addl $4, %%esp;\n" \
> - " pushl %[thunk_target];\n" \
> + "903: add $4, %%" _ASM_SP ";\n" \
> + " push %[thunk_target];\n" \
Yeah, don't do that.
> " ret;\n" \
> " .align 16\n" \
> "904: call 901b;\n", \
> - X86_FEATURE_RETPOLINE)
> + X86_FEATURE_RETPOLINE, \
> + "lfence;\n" \
> + ANNOTATE_RETPOLINE_SAFE \
> + "call *%[thunk_target]\n", \
> + X86_FEATURE_RETPOLINE_AMD)
And that's OK again.
next prev parent reply other threads:[~2018-09-18 9:50 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-18 5:17 [PATCH] x86/speculation: Use AMD specific retpoline for inline asm on AMD Zhenzhong Duan
2018-09-18 9:50 ` Peter Zijlstra [this message]
2018-09-18 10:31 ` Zhenzhong Duan
2018-09-18 10:59 ` Peter Zijlstra
2018-09-18 12:04 ` Zhenzhong Duan
2018-09-18 13:00 ` Peter Zijlstra
2018-09-18 13:03 ` Peter Zijlstra
2018-09-18 13:32 ` David Woodhouse
2018-09-18 14:41 ` Zhenzhong Duan
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