From: Borislav Petkov <bp@alien8.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: x86@kernel.org, tony.luck@intel.com, pjt@google.com,
linux-kernel@vger.kernel.org, r.marek@assembler.cz,
jpoimboe@redhat.com, jikos@kernel.org
Subject: Re: [RFC][PATCH 2/2] x86/retpoline: Compress retpolines
Date: Fri, 19 Feb 2021 08:14:39 +0100 [thread overview]
Message-ID: <20210219071439.GA26778@zn.tnic> (raw)
In-Reply-To: <20210218172151.942060087@infradead.org>
On Thu, Feb 18, 2021 at 05:59:40PM +0100, Peter Zijlstra wrote:
> By using int3 as a speculation fence instead of lfence, we can shrink
> the longest alternative to just 15 bytes:
>
> 0: e8 05 00 00 00 callq a <.altinstr_replacement+0xa>
> 5: f3 90 pause
> 7: cc int3
> 8: eb fb jmp 5 <.altinstr_replacement+0x5>
> a: 48 89 04 24 mov %rax,(%rsp)
> e: c3 retq
>
> This means we can change the alignment from 32 to 16 bytes and get 4
> retpolines per cacheline, $I win.
You mean I$ :)
In any case, for both:
Reviewed-by: Borislav Petkov <bp@suse.de>
and it looks real nice here, the size:
readelf -s vmlinux | grep __x86_indirect
78966: ffffffff81c023e0 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
81653: ffffffff81c02390 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
82338: ffffffff81c02430 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
82955: ffffffff81c02380 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
85057: ffffffff81c023f0 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
89996: ffffffff81c023a0 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
91094: ffffffff81c02400 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
91278: ffffffff81c023b0 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
92015: ffffffff81c02360 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
92722: ffffffff81c023c0 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
97062: ffffffff81c02410 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
98687: ffffffff81c023d0 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
99076: ffffffff81c02350 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
99500: ffffffff81c02370 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
100579: ffffffff81c02420 15 FUNC GLOBAL DEFAULT 1 __x86_indirect_t[...]
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2021-02-19 7:15 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-18 16:59 [RFC][PATCH 0/2] x86/retpoline: Retpoline on a diet Peter Zijlstra
2021-02-18 16:59 ` [RFC][PATCH 1/2] x86/retpoline: Simplify retpolines Peter Zijlstra
2021-02-22 11:36 ` Peter Zijlstra
2021-02-18 16:59 ` [RFC][PATCH 2/2] x86/retpoline: Compress retpolines Peter Zijlstra
2021-02-19 7:14 ` Borislav Petkov [this message]
2021-02-22 11:27 ` Peter Zijlstra
2021-02-18 18:46 ` [RFC PATCH] x86/retpolines: Prevent speculation after RET Borislav Petkov
2021-02-18 19:02 ` Peter Zijlstra
2021-02-18 19:11 ` Borislav Petkov
2021-02-19 8:15 ` Peter Zijlstra
2021-02-19 12:08 ` Andrew Cooper
2021-02-19 9:28 ` David Laight
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