From: Peter Zijlstra <peterz@infradead.org>
To: speck@linutronix.de
Subject: [MODERATED] Re: [patch V2 09/10] MDS basics+ 9
Date: Thu, 21 Feb 2019 12:50:07 +0100 [thread overview]
Message-ID: <20190221115007.GW32534@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190221110444.GD32477@hirez.programming.kicks-ass.net>
On Thu, Feb 21, 2019 at 12:04:44PM +0100, Peter Zijlstra wrote:
> On Wed, Feb 20, 2019 at 04:08:02PM +0100, speck for Thomas Gleixner wrote:
> > static inline void mds_user_clear_cpu_buffers(void)
> > {
> > + if (static_branch_likely(&mds_user_clear_cond)) {
> > + if (__this_cpu_read(mds_cond_clear)) {
> > + __this_cpu_write(mds_cond_clear, 0);
> > + mds_clear_cpu_buffers();
> > + }
> > + }
> > if (static_branch_likely(&mds_user_clear_always))
> > mds_clear_cpu_buffers();
> > }
>
> Results in:
>
> 998: e9 0b 00 00 00 jmpq 9a8 <prepare_exit_to_usermode+0x58>
> 99d: 65 8b 05 00 00 00 00 mov %gs:0x0(%rip),%eax # 9a4 <prepare_exit_to_usermode+0x54>
> 9a0: R_X86_64_PC32 mds_cond_clear-0x4
> 9a4: 85 c0 test %eax,%eax
> 9a6: 75 0f jne 9b7 <prepare_exit_to_usermode+0x67>
> 9a8: e9 07 00 00 00 jmpq 9b4 <prepare_exit_to_usermode+0x64>
> 9ad: 0f 00 2d 00 00 00 00 verw 0x0(%rip) # 9b4 <prepare_exit_to_usermode+0x64>
> 9b0: R_X86_64_PC32 .rodata-0x4
> 9b4: 5b pop %rbx
> 9b5: 5d pop %rbp
> 9b6: c3 retq
> 9b7: 65 c7 05 00 00 00 00 movl $0x0,%gs:0x0(%rip) # 9c2 <prepare_exit_to_usermode+0x72>
> 9be: 00 00 00 00
> 9ba: R_X86_64_PC32 mds_cond_clear-0x8
> 9c2: 0f 00 2d 00 00 00 00 verw 0x0(%rip) # 9c9 <prepare_exit_to_usermode+0x79>
> 9c5: R_X86_64_PC32 .rodata-0x4
> 9c9: eb dd jmp 9a8 <prepare_exit_to_usermode+0x58>
>
>
> static inline void mds_user_clear_cpu_buffers(void)
> {
> if (!static_branch_likely(&mds_user_clear_always))
> return;
>
> if (static_branch_likely(&mds_user_clear_cond)) {
> if (!__this_cpu_read(mds_cond_clear))
> return;
>
> __this_cpu_write(mds_cond_clear, 0);
> }
>
> mds_clear_cpu_buffers();
> }
>
> results in:
>
> 998: e9 22 00 00 00 jmpq 9bf <prepare_exit_to_usermode+0x6f>
> 99d: e9 16 00 00 00 jmpq 9b8 <prepare_exit_to_usermode+0x68>
> 9a2: 65 8b 05 00 00 00 00 mov %gs:0x0(%rip),%eax # 9a9 <prepare_exit_to_usermode+0x59>
> 9a5: R_X86_64_PC32 mds_cond_clear-0x4
> 9a9: 85 c0 test %eax,%eax
> 9ab: 74 12 je 9bf <prepare_exit_to_usermode+0x6f>
> 9ad: 65 c7 05 00 00 00 00 movl $0x0,%gs:0x0(%rip) # 9b8 <prepare_exit_to_usermode+0x68>
> 9b4: 00 00 00 00
> 9b0: R_X86_64_PC32 mds_cond_clear-0x8
> 9b8: 0f 00 2d 00 00 00 00 verw 0x0(%rip) # 9bf <prepare_exit_to_usermode+0x6f>
> 9bb: R_X86_64_PC32 .rodata-0x4
> 9bf:
>
>
> The only 'downside' is that means @mds_user_clear_always is now a
> misnomer (and needs be enabled for cond too).
static inline void mds_user_clear_cpu_buffers(void)
{
if (!static_branch_likely(&mds_user_clear_always))
return;
if (static_branch_likely(&mds_user_clear_cond)) {
if (!GEN_BINARY_RMWcc("btrl", mds_cond_clear, c, "Ir", 0, __percpu_arg([var])))
return;
}
mds_clear_cpu_buffers();
}
998: e9 17 00 00 00 jmpq 9b4 <prepare_exit_to_usermode+0x64>
99d: e9 0b 00 00 00 jmpq 9ad <prepare_exit_to_usermode+0x5d>
9a2: 65 0f ba 35 00 00 00 btrl $0x0,%gs:0x0(%rip) # 9ab <prepare_exit_to_usermode+0x5b>
9a9: 00 00
9a6: R_X86_64_PC32 mds_cond_clear-0x5
9ab: 73 07 jae 9b4 <prepare_exit_to_usermode+0x64>
9ad: 0f 00 2d 00 00 00 00 verw 0x0(%rip) # 9b4 <prepare_exit_to_usermode+0x64>
9b0: R_X86_64_PC32 .rodata-0x4
9b4:
But then the nectro-cult people will hate you :-) Also it will fail to
compile for old GCC and Steve's insane if() redefinition.
next prev parent reply other threads:[~2019-02-21 11:50 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-20 15:07 [patch V2 00/10] MDS basics+ 0 Thomas Gleixner
2019-02-20 15:07 ` [patch V2 01/10] MDS basics+ 1 Thomas Gleixner
2019-02-20 16:27 ` [MODERATED] " Borislav Petkov
2019-02-20 16:46 ` Greg KH
2019-02-20 15:07 ` [patch V2 02/10] MDS basics+ 2 Thomas Gleixner
2019-02-20 16:47 ` [MODERATED] " Borislav Petkov
2019-02-20 16:48 ` Greg KH
2019-02-20 15:07 ` [patch V2 03/10] MDS basics+ 3 Thomas Gleixner
2019-02-20 16:54 ` [MODERATED] " mark gross
2019-02-20 16:57 ` Thomas Gleixner
2019-02-20 18:08 ` [MODERATED] " mark gross
2019-02-20 21:40 ` Thomas Gleixner
2019-02-20 17:14 ` [MODERATED] " Borislav Petkov
2019-02-20 21:31 ` Thomas Gleixner
2019-02-21 2:12 ` [MODERATED] " Andrew Cooper
2019-02-21 9:27 ` Peter Zijlstra
2019-02-21 9:33 ` [MODERATED] " Borislav Petkov
2019-02-21 10:04 ` Thomas Gleixner
2019-02-21 10:18 ` [MODERATED] Re: " Borislav Petkov
2019-02-20 15:07 ` [patch V2 04/10] MDS basics+ 4 Thomas Gleixner
2019-02-20 16:52 ` [MODERATED] " Greg KH
2019-02-20 17:10 ` mark gross
2019-02-21 19:26 ` [MODERATED] Encrypted Message Tim Chen
2019-02-21 20:32 ` Thomas Gleixner
2019-02-21 21:07 ` [MODERATED] " Jiri Kosina
2019-02-20 18:43 ` [MODERATED] Re: [patch V2 04/10] MDS basics+ 4 Borislav Petkov
2019-02-20 19:26 ` Jiri Kosina
2019-02-20 21:42 ` Thomas Gleixner
2019-02-20 15:07 ` [patch V2 05/10] MDS basics+ 5 Thomas Gleixner
2019-02-20 20:05 ` [MODERATED] " Borislav Petkov
2019-02-21 2:24 ` Andrew Cooper
2019-02-21 10:36 ` Thomas Gleixner
2019-02-21 11:22 ` Thomas Gleixner
2019-02-21 11:51 ` [MODERATED] Attack Surface [Was [patch V2 05/10] MDS basics+ 5] Andrew Cooper
2019-02-21 18:41 ` Thomas Gleixner
2019-02-20 15:07 ` [patch V2 06/10] MDS basics+ 6 Thomas Gleixner
2019-02-21 10:18 ` [MODERATED] " Borislav Petkov
2019-02-20 15:08 ` [patch V2 07/10] MDS basics+ 7 Thomas Gleixner
2019-02-21 12:47 ` [MODERATED] " Borislav Petkov
2019-02-21 13:48 ` Thomas Gleixner
2019-02-20 15:08 ` [patch V2 08/10] MDS basics+ 8 Thomas Gleixner
2019-02-21 14:04 ` [MODERATED] " Borislav Petkov
2019-02-21 14:11 ` Thomas Gleixner
2019-02-20 15:08 ` [patch V2 09/10] MDS basics+ 9 Thomas Gleixner
2019-02-20 16:21 ` [MODERATED] " Peter Zijlstra
2019-02-20 22:32 ` Thomas Gleixner
2019-02-20 22:50 ` [MODERATED] " Jiri Kosina
2019-02-20 23:22 ` Thomas Gleixner
2019-02-21 11:04 ` [MODERATED] " Peter Zijlstra
2019-02-21 11:50 ` Peter Zijlstra [this message]
2019-02-21 14:18 ` Borislav Petkov
2019-02-21 18:00 ` Kees Cook
2019-02-21 19:46 ` Thomas Gleixner
2019-02-21 20:56 ` Thomas Gleixner
2019-02-20 15:08 ` [patch V2 10/10] MDS basics+ 10 Thomas Gleixner
2019-02-22 16:05 ` [MODERATED] Re: [patch V2 00/10] MDS basics+ 0 mark gross
2019-02-22 17:12 ` Thomas Gleixner
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