Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
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>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: [PATCH V3 33/49] x86/entry: Add the C version get_percpu_base()
Date:   Thu, 14 Oct 2021 11:41:05 +0800
Message-Id: <20211014034121.17025-2-jiangshanlai@gmail.com>
In-Reply-To: <20211014031413.14471-1-jiangshanlai@gmail.com>
References: <20211014031413.14471-1-jiangshanlai@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Lai Jiangshan <laijs@linux.alibaba.com>

It implements the C version of asm macro GET_PERCPU_BASE().

Not functional difference intended.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry64.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/arch/x86/entry/entry64.c b/arch/x86/entry/entry64.c
index 5edbb4bb4786..48fd3199f00b 100644
--- a/arch/x86/entry/entry64.c
+++ b/arch/x86/entry/entry64.c
@@ -201,3 +201,39 @@ struct pt_regs *error_entry(struct pt_regs *eregs)
 	/* Enter from kernel, don't move pt_regs */
 	return eregs;
 }
+
+#ifdef CONFIG_SMP
+/*
+ * CPU/node NR is loaded from the limit (size) field of a special segment
+ * descriptor entry in GDT.
+ *
+ * Do not use RDPID, because KVM loads guest's TSC_AUX on vm-entry and
+ * may not restore the host's value until the CPU returns to userspace.
+ * Thus the kernel would consume a guest's TSC_AUX if an NMI arrives
+ * while running KVM's run loop.
+ */
+static __always_inline unsigned int gdt_get_cpu(void)
+{
+	unsigned int p;
+
+	asm ("lsl %[seg],%[p]" : [p] "=a" (p) : [seg] "r" (__CPUNODE_SEG));
+
+	return p & VDSO_CPUNODE_MASK;
+}
+
+/*
+ * Fetch the per-CPU GSBASE value for this processor.
+ *
+ * We normally use %gs for accessing per-CPU data, but we are setting up
+ * %gs here and obviously can not use %gs itself to access per-CPU data.
+ */
+static __always_inline unsigned long get_percpu_base(void)
+{
+	return __per_cpu_offset[gdt_get_cpu()];
+}
+#else
+static __always_inline unsigned long get_percpu_base(void)
+{
+	return pcpu_unit_offsets;
+}
+#endif
-- 
2.19.1.6.gb485710b