linux-kernel - [PATCH V4 34/50] x86/entry: Add the C version get_percpu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20211026143436.19071-9-jiangshanlai@gmail.com>
Date:   Tue, 26 Oct 2021 22:34:20 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH V4 34/50] x86/entry: Add the C version get_percpu_base()

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

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

Not functional difference intended.

Signed-off-by: Lai Jiangshan <laijs@...ux.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 446d91d7b376..8f3a9f2d9c6a 100644
--- a/arch/x86/entry/entry64.c
+++ b/arch/x86/entry/entry64.c
@@ -187,3 +187,39 @@ 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