linux-kernel - Re: [PATCH V6 6/8] x86/entry: Convert SWAPGS to swapgs and remove the definition of SWAPGS

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Date:   Fri, 29 Apr 2022 14:22:15 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     Jürgen Gross <jgross@...e.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH V6 6/8] x86/entry: Convert SWAPGS to swapgs and remove
 the definition of SWAPGS

On Fri, Apr 29, 2022 at 07:45:43PM +0800, Lai Jiangshan wrote:
> Adding ALTERNATIVE in swapgs_restore_regs_and_return_to_usermode()

All I'm saying is to do this:

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index c5aeb0819707..79f0511a4791 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -140,7 +140,7 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
 	call	do_SYSENTER_32
 	/* XEN PV guests always use IRET path */
 	ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
-		    "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
+		    "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
 	jmp	sysret32_from_system_call
 
 .Lsysenter_fix_flags:

which eliminates one JMP in the XENPV case if the CONFIG_DEBUG_ENTRY
thing is not relevant to XENPV.

But let's see what Jürgen says first...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette