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 30/49] x86/entry: Add the C version ist_switch_to_kernel_cr3()
Date:   Fri, 26 Nov 2021 18:11:50 +0800
Message-Id: <20211126101209.8613-31-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>

It switches the CR3 to kernel CR3 and returns the original CR3, and
the caller should save the return value.

It is the C version of SAVE_AND_SWITCH_TO_KERNEL_CR3.

Not functional difference intended.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry64.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/entry/entry64.c b/arch/x86/entry/entry64.c
index 0dc63ae8153a..283bd685a275 100644
--- a/arch/x86/entry/entry64.c
+++ b/arch/x86/entry/entry64.c
@@ -35,8 +35,23 @@ static __always_inline void switch_to_kernel_cr3(void)
 	if (static_cpu_has(X86_FEATURE_PTI))
 		pti_switch_to_kernel_cr3(__native_read_cr3());
 }
+
+static __always_inline unsigned long ist_switch_to_kernel_cr3(void)
+{
+	unsigned long cr3 = 0;
+
+	if (static_cpu_has(X86_FEATURE_PTI)) {
+		cr3 = __native_read_cr3();
+
+		if (cr3 & PTI_USER_PGTABLE_MASK)
+			pti_switch_to_kernel_cr3(cr3);
+	}
+
+	return cr3;
+}
 #else
 static __always_inline void switch_to_kernel_cr3(void) {}
+static __always_inline unsigned long ist_switch_to_kernel_cr3(void) { return 0; }
 #endif
 
 /*
-- 
2.19.1.6.gb485710b