From: "Jürgen Groß" <jgross@suse.com>
To: Borislav Petkov <bp@alien8.de>
Cc: xen-devel@lists.xenproject.org, x86@kernel.org,
linux-kernel@vger.kernel.org, peterz@infradead.org,
luto@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2 07/12] x86: add new features for paravirt patching
Date: Wed, 9 Dec 2020 13:22:24 +0100 [thread overview]
Message-ID: <9e989b07-84e8-b07b-ba6e-c2a3ed19d7b1@suse.com> (raw)
In-Reply-To: <20201209120307.GB18203@zn.tnic>
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On 09.12.20 13:03, Borislav Petkov wrote:
> On Wed, Dec 09, 2020 at 08:30:53AM +0100, Jürgen Groß wrote:
>> Hey, I already suggested to use ~FEATURE for that purpose (see
>> https://lore.kernel.org/lkml/f105a63d-6b51-3afb-83e0-e899ea40813e@suse.com/
>
> Great minds think alike!
>
> :-P
>
>> I'd rather make the syntax:
>>
>> ALTERNATIVE_TERNARY <initial-code> <feature> <code-for-feature-set>
>> <code-for-feature-unset>
>>
>> as this ...
>
> Sure, that is ok too.
>
>> ... would match perfectly to this interpretation.
>
> Yap.
>
>> Hmm, using flags is an alternative (pun intended :-) ).
>
> LOL!
>
> Btw, pls do check how much the vmlinux size of an allyesconfig grows
> with this as we will be adding a byte per patch site. Not that it would
> matter too much - the flags are a long way a comin'. :-)
>
>> No, this is needed for non-Xen cases, too (especially pv spinlocks).
>
> I see.
>
>>> Can you give an example here pls why the paravirt patching needs to run
>>> first?
>>
>> Okay.
>
> I meant an example for me to have a look at. :)
>
> If possible pls.
Ah, okay.
Lets take the spin_unlock() case. With patch 11 of the series this is
PVOP_ALT_VCALLEE1(lock.queued_spin_unlock, lock,
"movb $0, (%%" _ASM_ARG1 ");",
X86_FEATURE_NO_PVUNLOCK);
which boils down to ALTERNATIVE "call *lock.queued_spin_unlock"
"movb $0,(%rdi)" X86_FEATURE_NO_PVUNLOCK
The initial (paravirt) code is an indirect call in order to allow
spin_unlock() before paravirt/alternative patching takes place.
Paravirt patching will then replace the indirect call with a direct call
to the correct unlock function. Then alternative patching might replace
the direct call to the bare metal unlock with a plain "movb $0,(%rdi)"
in case pvlocks are not enabled.
In case alternative patching would occur first, the indirect call might
be replaced with the "movb ...", and then paravirt patching would
clobber that with the direct call, resulting in the bare metal
optimization being removed again.
Juergen
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next prev parent reply other threads:[~2020-12-09 12:23 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-20 11:46 [PATCH v2 00/12] x86: major paravirt cleanup Juergen Gross
2020-11-20 11:46 ` [PATCH v2 01/12] x86/xen: use specific Xen pv interrupt entry for MCE Juergen Gross
2020-12-09 21:03 ` Thomas Gleixner
2020-11-20 11:46 ` [PATCH v2 02/12] x86/xen: use specific Xen pv interrupt entry for DF Juergen Gross
2020-12-09 21:03 ` Thomas Gleixner
2020-11-20 11:46 ` [PATCH v2 03/12] x86/pv: switch SWAPGS to ALTERNATIVE Juergen Gross
2020-11-27 11:31 ` Borislav Petkov
2020-12-09 21:07 ` Thomas Gleixner
2020-11-20 11:46 ` [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call Juergen Gross
2020-12-02 12:32 ` Borislav Petkov
2020-12-02 14:48 ` Jürgen Groß
2020-12-02 17:08 ` Borislav Petkov
2020-11-20 11:46 ` [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf Juergen Gross
2020-11-20 11:59 ` Peter Zijlstra
2020-11-20 12:05 ` Jürgen Groß
2020-11-22 6:55 ` Jürgen Groß
2020-11-22 21:44 ` Andy Lutomirski
2020-11-23 5:21 ` Jürgen Groß
2020-11-23 15:15 ` Andy Lutomirski
2020-12-09 13:27 ` Mark Rutland
2020-12-09 14:02 ` Mark Rutland
2020-12-09 14:05 ` Jürgen Groß
2020-12-09 18:15 ` Mark Rutland
2020-12-09 18:54 ` Thomas Gleixner
2020-12-10 11:10 ` Mark Rutland
2020-12-10 20:15 ` x86/ioapic: Cleanup the timer_works() irqflags mess Thomas Gleixner
2020-12-10 22:04 ` [tip: x86/apic] " tip-bot2 for Thomas Gleixner
2020-12-11 5:10 ` Jürgen Groß
2020-11-27 2:20 ` [x86] 97e8f0134a: fio.write_iops 8.6% improvement kernel test robot
2020-11-20 11:46 ` [PATCH v2 06/12] x86/paravirt: switch time pvops functions to use static_call() Juergen Gross
2020-11-20 12:01 ` Peter Zijlstra
2020-11-20 12:07 ` Jürgen Groß
2020-11-20 11:46 ` [PATCH v2 07/12] x86: add new features for paravirt patching Juergen Gross
2020-12-08 18:43 ` Borislav Petkov
2020-12-09 7:30 ` Jürgen Groß
2020-12-09 12:03 ` Borislav Petkov
2020-12-09 12:22 ` Jürgen Groß [this message]
2020-12-10 17:58 ` Borislav Petkov
2020-11-20 11:46 ` [PATCH v2 08/12] x86/paravirt: remove no longer needed 32-bit pvops cruft Juergen Gross
2020-11-20 12:08 ` Peter Zijlstra
2020-11-20 12:16 ` Jürgen Groß
2020-11-20 16:52 ` Arvind Sankar
2020-11-20 11:46 ` [PATCH v2 09/12] x86/paravirt: switch iret pvops to ALTERNATIVE Juergen Gross
2020-11-20 11:46 ` [PATCH v2 10/12] x86/paravirt: add new macros PVOP_ALT* supporting pvops in ALTERNATIVEs Juergen Gross
2020-11-20 11:46 ` [PATCH v2 11/12] x86/paravirt: switch functions with custom code to ALTERNATIVE Juergen Gross
2020-11-20 15:46 ` kernel test robot
2020-11-25 15:46 ` [x86/paravirt] fd8d46a7a2: kernel-selftests.livepatch.test-callbacks.sh.fail kernel test robot
2020-11-20 11:46 ` [PATCH v2 12/12] x86/paravirt: have only one paravirt patch function Juergen Gross
2020-11-20 14:18 ` kernel test robot
2020-11-20 12:53 ` [PATCH v2 00/12] x86: major paravirt cleanup Peter Zijlstra
2020-11-23 13:43 ` Peter Zijlstra
2020-12-15 11:42 ` Jürgen Groß
2020-12-15 14:18 ` Peter Zijlstra
2020-12-15 14:54 ` Peter Zijlstra
2020-12-15 15:07 ` Jürgen Groß
2020-12-16 0:38 ` Josh Poimboeuf
2020-12-16 8:40 ` Peter Zijlstra
2020-12-16 16:56 ` Josh Poimboeuf
2020-12-16 17:58 ` Peter Zijlstra
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