linux-kernel - [patch V6 15/37] x86/entry: Change exit path of xen_failsafe

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Date:   Sat, 16 May 2020 01:46:02 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [patch V6 15/37] x86/entry: Change exit path of xen_failsafe_callback


xen_failsafe_callback is invoked from XEN for two cases:

  1. Fault while reloading DS, ES, FS or GS
  2. Fault while executing IRET

#1 retries the IRET after XEN has fixed up the segments.
#2 injects a #GP which kills the task

For #1 there is no reason to go through the full exception return path
because the tasks TIF state is still the same. So just going straight to
the IRET path is good enough.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Juergen Gross <jgross@...e.com>

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index dd8064ffdf12..65fd41fe77d9 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -1352,7 +1352,7 @@ SYM_FUNC_START(xen_failsafe_callback)
 5:	pushl	$-1				/* orig_ax = -1 => not a system call */
 	SAVE_ALL
 	ENCODE_FRAME_POINTER
-	jmp	ret_from_exception
+	jmp	handle_exception_return
 
 .section .fixup, "ax"
 6:	xorl	%eax, %eax
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 1157d63b3682..55f612032793 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1175,7 +1175,7 @@ SYM_CODE_START(xen_failsafe_callback)
 	pushq	$-1 /* orig_ax = -1 => not a system call */
 	PUSH_AND_CLEAR_REGS
 	ENCODE_FRAME_POINTER
-	jmp	error_exit
+	jmp	error_return
 SYM_CODE_END(xen_failsafe_callback)
 #endif /* CONFIG_XEN_PV */