From: Borislav Petkov <bp@alien8.de>
To: "Jürgen Groß" <jgross@suse.com>
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: Thu, 10 Dec 2020 18:58:46 +0100 [thread overview]
Message-ID: <20201210175846.GE26529@zn.tnic> (raw)
In-Reply-To: <9e989b07-84e8-b07b-ba6e-c2a3ed19d7b1@suse.com>
On Wed, Dec 09, 2020 at 01:22:24PM +0100, Jürgen Groß wrote:
> 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.
Aha, that zeros the locking var on unlock, I see.
> 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.
Yeah, that explains the whole situation much better - thanks - and
considering how complex the whole patching is, I wouldn't mind the gist
of it as text in alternative_instructions() or in a comment above it so
that we don't have to swap everything back in, months and years from
now, when we optimize it yet again. :-}
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2020-12-10 17:59 UTC|newest]
Thread overview: 106+ 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 ` Juergen Gross via Virtualization
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 via Virtualization
2020-11-20 11:46 ` Juergen Gross
2020-11-27 11:31 ` Borislav Petkov
2020-11-27 11:31 ` Borislav Petkov
2020-12-09 21:07 ` Thomas Gleixner
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 via Virtualization
2020-11-20 11:46 ` Juergen Gross
2020-12-02 12:32 ` Borislav Petkov
2020-12-02 12:32 ` Borislav Petkov
2020-12-02 14:48 ` Jürgen Groß via Virtualization
2020-12-02 14:48 ` Jürgen Groß
2020-12-02 17:08 ` Borislav Petkov
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 via Virtualization
2020-11-20 11:46 ` Juergen Gross
2020-11-20 11:59 ` Peter Zijlstra
2020-11-20 11:59 ` Peter Zijlstra
2020-11-20 12:05 ` Jürgen Groß via Virtualization
2020-11-20 12:05 ` Jürgen Groß
2020-11-22 6:55 ` Jürgen Groß via Virtualization
2020-11-22 6:55 ` Jürgen Groß
2020-11-22 21:44 ` Andy Lutomirski
2020-11-22 21:44 ` Andy Lutomirski
2020-11-23 5:21 ` Jürgen Groß via Virtualization
2020-11-23 5:21 ` Jürgen Groß
2020-11-23 15:15 ` Andy Lutomirski
2020-11-23 15:15 ` Andy Lutomirski
2020-12-09 13:27 ` Mark Rutland
2020-12-09 13:27 ` Mark Rutland
2020-12-09 14:02 ` Mark Rutland
2020-12-09 14:02 ` Mark Rutland
2020-12-09 14:05 ` Jürgen Groß via Virtualization
2020-12-09 14:05 ` Jürgen Groß
2020-12-09 18:15 ` Mark Rutland
2020-12-09 18:15 ` Mark Rutland
2020-12-09 18:54 ` Thomas Gleixner
2020-12-09 18:54 ` Thomas Gleixner
2020-12-10 11:10 ` Mark Rutland
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 20:15 ` Thomas Gleixner
2020-12-10 22:04 ` [tip: x86/apic] " tip-bot2 for Thomas Gleixner
2020-12-11 5:10 ` Jürgen Groß via Virtualization
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 11:46 ` Juergen Gross via Virtualization
2020-11-20 12:01 ` Peter Zijlstra
2020-11-20 12:01 ` Peter Zijlstra
2020-11-20 12:07 ` Jürgen Groß
2020-11-20 12:07 ` Jürgen Groß via Virtualization
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
2020-12-10 17:58 ` Borislav Petkov [this message]
2020-11-20 11:46 ` [PATCH v2 08/12] x86/paravirt: remove no longer needed 32-bit pvops cruft Juergen Gross via Virtualization
2020-11-20 11:46 ` Juergen Gross
2020-11-20 12:08 ` Peter Zijlstra
2020-11-20 12:08 ` Peter Zijlstra
2020-11-20 12:16 ` Jürgen Groß via Virtualization
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 via Virtualization
2020-11-20 11:46 ` Juergen Gross
2020-11-20 11:46 ` [PATCH v2 10/12] x86/paravirt: add new macros PVOP_ALT* supporting pvops in ALTERNATIVEs Juergen Gross via Virtualization
2020-11-20 11:46 ` Juergen Gross
2020-11-20 11:46 ` [PATCH v2 11/12] x86/paravirt: switch functions with custom code to ALTERNATIVE Juergen Gross via Virtualization
2020-11-20 11:46 ` Juergen Gross
2020-11-20 15:46 ` kernel test robot
2020-11-20 15:46 ` kernel test robot
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 via Virtualization
2020-11-20 11:46 ` Juergen Gross
2020-11-20 14:18 ` kernel test robot
2020-11-20 14:18 ` kernel test robot
2020-11-20 14:18 ` kernel test robot
2020-11-20 12:53 ` [PATCH v2 00/12] x86: major paravirt cleanup Peter Zijlstra
2020-11-20 12:53 ` Peter Zijlstra
2020-11-23 13:43 ` Peter Zijlstra
2020-11-23 13:43 ` Peter Zijlstra
2020-12-15 11:42 ` Jürgen Groß
2020-12-15 11:42 ` Jürgen Groß via Virtualization
2020-12-15 14:18 ` Peter Zijlstra
2020-12-15 14:18 ` Peter Zijlstra
2020-12-15 14:54 ` Peter Zijlstra
2020-12-15 14:54 ` Peter Zijlstra
2020-12-15 15:07 ` Jürgen Groß
2020-12-15 15:07 ` Jürgen Groß via Virtualization
2020-12-16 0:38 ` Josh Poimboeuf
2020-12-16 0:38 ` Josh Poimboeuf
2020-12-16 8:40 ` Peter Zijlstra
2020-12-16 8:40 ` Peter Zijlstra
2020-12-16 16:56 ` Josh Poimboeuf
2020-12-16 16:56 ` Josh Poimboeuf
2020-12-16 17:58 ` Peter Zijlstra
2020-12-16 17:58 ` Peter Zijlstra
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