linux-kernel - [PATCH V6 5/8] x86/entry: Don't call error

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Date:   Thu, 21 Apr 2022 22:10:52 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Juergen Gross <jgross@...e.com>, 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>
Subject: [PATCH V6 5/8] x86/entry: Don't call error_entry() for XENPV

From: Lai Jiangshan <jiangshan.ljs@...group.com>

When in XENPV, it is already in the task stack, and it can't fault for
native_iret() nor native_load_gs_index() since XENPV uses its own pvops
for IRET and load_gs_index().  And it doesn't need to switch the CR3.

So there is no reason to call error_entry() in XENPV.

Cc: Juergen Gross <jgross@...e.com>
Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
---
 arch/x86/entry/entry_64.S | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index ab6ab6d3dab5..062aa9d95961 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -336,8 +336,17 @@ SYM_CODE_END(push_and_clear_regs)
 	call push_and_clear_regs
 	UNWIND_HINT_REGS
 
-	call	error_entry
-	movq	%rax, %rsp			/* switch to the task stack if from userspace */
+	/*
+	 * Call error_entry() and switch to the task stack if from userspace.
+	 *
+	 * When in XENPV, it is already in the task stack, and it can't fault
+	 * for native_iret() nor native_load_gs_index() since XENPV uses its
+	 * own pvops for IRET and load_gs_index().  And it doesn't need to
+	 * switch the CR3.  So it can skip invoking error_entry().
+	 */
+	ALTERNATIVE "call error_entry; movq %rax, %rsp", \
+		"", X86_FEATURE_XENPV
+
 	ENCODE_FRAME_POINTER
 	UNWIND_HINT_REGS
 
-- 
2.19.1.6.gb485710b