From: Borislav Petkov <bp@alien8.de>
To: Juergen Gross <jgross@suse.com>
Cc: xen-devel@lists.xenproject.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org, peterz@infradead.org,
luto@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Deep Shah <sdeep@vmware.com>,
"VMware, Inc." <pv-drivers@vmware.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Stefano Stabellini <sstabellini@kernel.org>
Subject: Re: [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call
Date: Wed, 2 Dec 2020 13:32:35 +0100 [thread overview]
Message-ID: <20201202123235.GD2951@zn.tnic> (raw)
In-Reply-To: <20201120114630.13552-5-jgross@suse.com>
On Fri, Nov 20, 2020 at 12:46:22PM +0100, Juergen Gross wrote:
> @@ -123,12 +115,15 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
> * Try to use SYSRET instead of IRET if we're returning to
> * a completely clean 64-bit userspace context. If we're not,
> * go to the slow exit path.
> + * In the Xen PV case we must use iret anyway.
> */
> - movq RCX(%rsp), %rcx
> - movq RIP(%rsp), %r11
>
> - cmpq %rcx, %r11 /* SYSRET requires RCX == RIP */
> - jne swapgs_restore_regs_and_return_to_usermode
> + ALTERNATIVE __stringify( \
> + movq RCX(%rsp), %rcx; \
> + movq RIP(%rsp), %r11; \
> + cmpq %rcx, %r11; /* SYSRET requires RCX == RIP */ \
> + jne swapgs_restore_regs_and_return_to_usermode), \
> + "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
Why such a big ALTERNATIVE when you can simply do:
/*
* Try to use SYSRET instead of IRET if we're returning to
* a completely clean 64-bit userspace context. If we're not,
* go to the slow exit path.
* In the Xen PV case we must use iret anyway.
*/
ALTERNATIVE "", "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
movq RCX(%rsp), %rcx;
movq RIP(%rsp), %r11;
cmpq %rcx, %r11; /* SYSRET requires RCX == RIP */ \
jne swapgs_restore_regs_and_return_to_usermode
?
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
WARNING: multiple messages have this Message-ID (diff)
From: Borislav Petkov <bp@alien8.de>
To: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
peterz@infradead.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org, "VMware,
Inc." <pv-drivers@vmware.com>, Ingo Molnar <mingo@redhat.com>,
luto@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
xen-devel@lists.xenproject.org,
Thomas Gleixner <tglx@linutronix.de>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call
Date: Wed, 2 Dec 2020 13:32:35 +0100 [thread overview]
Message-ID: <20201202123235.GD2951@zn.tnic> (raw)
In-Reply-To: <20201120114630.13552-5-jgross@suse.com>
On Fri, Nov 20, 2020 at 12:46:22PM +0100, Juergen Gross wrote:
> @@ -123,12 +115,15 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
> * Try to use SYSRET instead of IRET if we're returning to
> * a completely clean 64-bit userspace context. If we're not,
> * go to the slow exit path.
> + * In the Xen PV case we must use iret anyway.
> */
> - movq RCX(%rsp), %rcx
> - movq RIP(%rsp), %r11
>
> - cmpq %rcx, %r11 /* SYSRET requires RCX == RIP */
> - jne swapgs_restore_regs_and_return_to_usermode
> + ALTERNATIVE __stringify( \
> + movq RCX(%rsp), %rcx; \
> + movq RIP(%rsp), %r11; \
> + cmpq %rcx, %r11; /* SYSRET requires RCX == RIP */ \
> + jne swapgs_restore_regs_and_return_to_usermode), \
> + "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
Why such a big ALTERNATIVE when you can simply do:
/*
* Try to use SYSRET instead of IRET if we're returning to
* a completely clean 64-bit userspace context. If we're not,
* go to the slow exit path.
* In the Xen PV case we must use iret anyway.
*/
ALTERNATIVE "", "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
movq RCX(%rsp), %rcx;
movq RIP(%rsp), %r11;
cmpq %rcx, %r11; /* SYSRET requires RCX == RIP */ \
jne swapgs_restore_regs_and_return_to_usermode
?
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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next prev parent reply other threads:[~2020-12-02 12:33 UTC|newest]
Thread overview: 107+ 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
2020-11-20 11:46 ` Juergen Gross via Virtualization
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
2020-11-20 11:46 ` Juergen Gross via Virtualization
2020-12-02 12:32 ` Borislav Petkov [this message]
2020-12-02 12:32 ` Borislav Petkov
2020-12-02 14:48 ` Jürgen Groß
2020-12-02 14:48 ` Jürgen Groß via Virtualization
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
2020-11-20 11:46 ` Juergen Gross via Virtualization
2020-11-20 11:59 ` Peter Zijlstra
2020-11-20 11:59 ` Peter Zijlstra
2020-11-20 12:05 ` Jürgen Groß
2020-11-20 12:05 ` Jürgen Groß via Virtualization
2020-11-22 6:55 ` Jürgen Groß
2020-11-22 6:55 ` Jürgen Groß via Virtualization
2020-11-22 21:44 ` Andy Lutomirski
2020-11-22 21:44 ` Andy Lutomirski
2020-11-22 21:44 ` Andy Lutomirski
2020-11-23 5:21 ` Jürgen Groß
2020-11-23 5:21 ` Jürgen Groß via Virtualization
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
2020-12-09 14:05 ` Jürgen Groß via Virtualization
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
2020-12-11 5:10 ` Jürgen Groß via Virtualization
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
2020-11-20 11:46 ` [PATCH v2 08/12] x86/paravirt: remove no longer needed 32-bit pvops cruft Juergen Gross
2020-11-20 11:46 ` Juergen Gross via Virtualization
2020-11-20 12:08 ` Peter Zijlstra
2020-11-20 12:08 ` Peter Zijlstra
2020-11-20 12:16 ` Jürgen Groß
2020-11-20 12:16 ` Jürgen Groß via Virtualization
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 ` Juergen Gross via Virtualization
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 ` Juergen Gross via Virtualization
2020-11-20 11:46 ` [PATCH v2 11/12] x86/paravirt: switch functions with custom code to ALTERNATIVE Juergen Gross
2020-11-20 11:46 ` Juergen Gross via Virtualization
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
2020-11-20 11:46 ` Juergen Gross via Virtualization
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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