From:   Lai Jiangshan <jiangshanlai@gmail.com>
To:     linux-kernel@vger.kernel.org
Cc:     x86@kernel.org, Lai Jiangshan <laijs@linux.alibaba.com>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: [PATCH V6 21/49] x86/entry: Don't call error_entry for XENPV
Date:   Fri, 26 Nov 2021 18:11:41 +0800
Message-Id: <20211126101209.8613-22-jiangshanlai@gmail.com>
In-Reply-To: <20211126101209.8613-1-jiangshanlai@gmail.com>
References: <20211126101209.8613-1-jiangshanlai@gmail.com>
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From: Lai Jiangshan <laijs@linux.alibaba.com>

When in XENPV, it is already in the task stack, and it can't fault
at native_irq_return_iret nor asm_load_gs_index_gs_change since
XENPV uses its own pvops for iret and load_gs_index().  And it
doesn't need to switch CR3.  So it can skip invoking error_entry().

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.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 09bd77e49249..c09e5a4dfbbf 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -325,8 +325,17 @@ SYM_CODE_END(ret_from_fork)
 	PUSH_AND_CLEAR_REGS
 	ENCODE_FRAME_POINTER
 
-	call	error_entry
-	movq	%rax, %rsp			/* switch stack settled by sync_regs() */
+	/*
+	 * Call error_entry and switch stack settled by sync_regs().
+	 *
+	 * When in XENPV, it is already in the task stack, and it can't fault
+	 * at native_irq_return_iret nor asm_load_gs_index_gs_change since
+	 * XENPV uses its own pvops for iret and load_gs_index().  And it
+	 * doesn't need to switch 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