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From: Lai Jiangshan <laijs@linux.alibaba.com>
To: Borislav Petkov <bp@alien8.de>, Lai Jiangshan <jiangshanlai@gmail.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
	Jan Beulich <jbeulich@suse.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Juergen Gross <jgross@suse.com>, Peter Anvin <hpa@zytor.com>,
	xen-devel@lists.xenproject.org, Andy Lutomirski <luto@kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Stefano Stabellini <sstabellini@kernel.org>
Subject: Re: [PATCH V4 04/50] x86/xen: Add xenpv_restore_regs_and_return_to_usermode()
Date: Tue, 2 Nov 2021 17:19:46 +0800	[thread overview]
Message-ID: <d4ae23dd-377e-8316-909b-d5bdeacc0904@linux.alibaba.com> (raw)
In-Reply-To: <YYD9ohN2Zcy4EdMb@zn.tnic>



On 2021/11/2 16:58, Borislav Petkov wrote:

>>   	 */
>>   
>> -	ALTERNATIVE "", "jmp	swapgs_restore_regs_and_return_to_usermode", \
>> +	ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", \
> 
> Instead of sprinkling all those ALTERNATIVE calls everywhere,
> why don't you simply jump to the xenpv-one at the
> swapgs_restore_regs_and_return_to_usermode label itself and have a
> single ALTERNATIVE there?
> 

It will add a 5-byte NOP at the beginning of the native
swapgs_restore_regs_and_return_to_usermode.  I avoided adding unneeded
code in the native code even if it is NOPs and avoided melting xenpv-one into
the native one which will reduce the code readability.

I will follow your preference since a 5-byte NOP is so negligible in the slow
path with an iret instruction.

Or other option that adds macros to wrap the ALTERNATIVE.
RESTORE_REGS_AND_RETURN_TO_USERMODE and
COND_RESTORE_REGS_AND_RETURN_TO_USERMODE (test %eax before jmp in native case)



  reply	other threads:[~2021-11-02  9:19 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-26 14:13 [PATCH V4 00/50] x86/entry/64: Convert a bunch of ASM entry code into C code Lai Jiangshan
2021-10-26 14:13 ` [PATCH V4 01/50] x86/entry: Add fence for kernel entry swapgs in paranoid_entry() Lai Jiangshan
2021-10-27 12:19   ` Borislav Petkov
2021-10-28  0:51     ` Lai Jiangshan
2021-10-26 14:13 ` [PATCH V4 02/50] x86/entry: Use the correct fence macro after swapgs in kernel CR3 Lai Jiangshan
2021-10-26 14:13 ` [PATCH V4 03/50] x86/traps: Remove stack-protector from traps.c Lai Jiangshan
2021-10-26 14:13 ` [PATCH V4 04/50] x86/xen: Add xenpv_restore_regs_and_return_to_usermode() Lai Jiangshan
2021-11-02  8:58   ` Borislav Petkov
2021-11-02  9:19     ` Lai Jiangshan [this message]
2021-11-02  9:49       ` Borislav Petkov
2021-11-02 11:22         ` H. Peter Anvin
2021-11-02 14:27           ` Borislav Petkov
2021-10-26 14:20 ` [PATCH V4 05/50] x86/entry: Use swapgs and native_iret directly in swapgs_restore_regs_and_return_to_usermode Lai Jiangshan
2021-10-26 14:20 ` [PATCH V4 06/50] compiler_types.h: Add __noinstr_section() for noinstr Lai Jiangshan
2021-10-26 14:24   ` Miguel Ojeda
2021-10-26 14:20 ` [PATCH V4 07/50] x86/entry: Introduce __entry_text for entry code written in C Lai Jiangshan
2021-10-26 14:20 ` [PATCH V4 08/50] x86/entry: Move PTI_USER_* to arch/x86/include/asm/processor-flags.h Lai Jiangshan
2021-10-26 14:20 ` [PATCH V4 09/50] x86: Remove unused kernel_to_user_p4dp() and user_to_kernel_p4dp() Lai Jiangshan
2021-10-26 14:20 ` [PATCH V4 10/50] x86: Replace PTI_PGTABLE_SWITCH_BIT with PTI_USER_PGTABLE_BIT Lai Jiangshan
2021-10-26 14:27 ` [PATCH V4 11/50] x86: Mark __native_read_cr3() & native_write_cr3() as __always_inline Lai Jiangshan
2021-10-26 14:27 ` [PATCH V4 12/50] x86/traps: Move the declaration of native_irq_return_iret into proto.h Lai Jiangshan
2021-10-26 14:27 ` [PATCH V4 13/50] x86/entry: Add arch/x86/entry/entry64.c for C entry code Lai Jiangshan
2021-10-26 14:27 ` [PATCH V4 14/50] x86/entry: Expose the address of .Lgs_change to entry64.c Lai Jiangshan
2021-10-26 14:27 ` [PATCH V4 15/50] x86/entry: Add C verion of SWITCH_TO_KERNEL_CR3 as switch_to_kernel_cr3() Lai Jiangshan
2021-10-26 14:27 ` [PATCH V4 16/50] x86/traps: Add fence_swapgs_{user,kernel}_entry() Lai Jiangshan
2021-10-26 14:27 ` [PATCH V4 17/50] x86/entry: Add C {user,kernel}_entry_swapgs_and_fence() Lai Jiangshan
2021-10-26 14:27 ` [PATCH V4 18/50] x86/traps: Move pt_regs only in fixup_bad_iret() Lai Jiangshan
2021-10-26 14:30 ` [PATCH V4 19/50] x86/entry: Switch the stack after error_entry() returns Lai Jiangshan
2021-10-26 14:30 ` [PATCH V4 20/50] x86/entry: move PUSH_AND_CLEAR_REGS out of error_entry Lai Jiangshan
2021-10-26 14:30 ` [PATCH V4 21/50] x86/entry: Move cld to the start of idtentry Lai Jiangshan
2021-10-26 14:30 ` [PATCH V4 22/50] x86/entry: Don't call error_entry for XENPV Lai Jiangshan
2021-10-26 14:30 ` [PATCH V4 23/50] x86/entry: Convert SWAPGS to swapgs in error_entry() Lai Jiangshan
2021-10-26 14:32 ` [PATCH V4 24/50] x86/entry: Implement the whole error_entry() as C code Lai Jiangshan
2021-10-26 14:32 ` [PATCH V4 25/50] x86/entry: Use idtentry macro for entry_INT80_compat Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 26/50] x86/entry: Convert SWAPGS to swapgs in entry_SYSENTER_compat() Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 27/50] x86: Remove the definition of SWAPGS Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 28/50] x86/entry: Make paranoid_exit() callable Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 29/50] x86/entry: Call paranoid_exit() in asm_exc_nmi() Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 30/50] x86/entry: move PUSH_AND_CLEAR_REGS out of paranoid_entry Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 31/50] x86/entry: Add the C version ist_switch_to_kernel_cr3() Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 32/50] x86/entry: Skip CR3 write when the saved CR3 is kernel CR3 in RESTORE_CR3 Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 33/50] x86/entry: Add the C version ist_restore_cr3() Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 34/50] x86/entry: Add the C version get_percpu_base() Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 35/50] x86/entry: Add the C version ist_switch_to_kernel_gsbase() Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 36/50] x86/entry: Implement the C version ist_paranoid_entry() Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 37/50] x86/entry: Implement the C version ist_paranoid_exit() Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 38/50] x86/entry: Add a C macro to define the function body for IST in .entry.text Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 39/50] x86/debug, mce: Use C entry code Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 40/50] x86/idtentry.h: Move the definitions *IDTENTRY_{MCE|DEBUG}* up Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 41/50] x86/nmi: Use DEFINE_IDTENTRY_NMI for nmi Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 42/50] x86/nmi: Use C entry code Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 43/50] x86/entry: Add a C macro to define the function body for IST in .entry.text with an error code Lai Jiangshan
2021-10-26 14:34 ` [PATCH V4 44/50] x86/doublefault: Use C entry code Lai Jiangshan
2021-10-26 14:38 ` [PATCH V4 45/50] x86/sev: Add and use ist_vc_switch_off_ist() Lai Jiangshan
2021-10-26 14:38 ` [PATCH V4 46/50] x86/sev: Use C entry code Lai Jiangshan
2021-10-26 14:38 ` [PATCH V4 47/50] x86/entry: Remove ASM function paranoid_entry() and paranoid_exit() Lai Jiangshan
2021-10-26 14:38 ` [PATCH V4 48/50] x86/entry: Remove the unused ASM macros Lai Jiangshan
2021-10-26 14:38 ` [PATCH V4 49/50] x86/entry: Remove save_ret from PUSH_AND_CLEAR_REGS Lai Jiangshan
2021-10-26 14:38 ` [PATCH V4 50/50] x86/syscall/64: Move the checking for sysret to C code Lai Jiangshan

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