[kvm-unit-tests PATCH 5/8] x86: Add proper helpers for per-cpu reads/writes

From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, Sean Christopherson <seanjc@google.com>
Subject: [kvm-unit-tests PATCH 5/8] x86: Add proper helpers for per-cpu reads/writes
Date: Fri, 21 Jan 2022 23:18:49 +0000	[thread overview]
Message-ID: <20220121231852.1439917-6-seanjc@google.com> (raw)
In-Reply-To: <20220121231852.1439917-1-seanjc@google.com>

Add helpers to read/write per-cpu data instead of open coding access
with gs: and magic numbers.  Keeping track of what offsets are used for
what and by whom is a nightmare.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 lib/x86/desc.c | 23 ++++++------------
 lib/x86/smp.c  |  7 ++----
 lib/x86/smp.h  | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 74 insertions(+), 21 deletions(-)

diff --git a/lib/x86/desc.c b/lib/x86/desc.c
index 25c5ac55..22ff59e9 100644
--- a/lib/x86/desc.c
+++ b/lib/x86/desc.c
@@ -1,6 +1,7 @@
 #include "libcflat.h"
 #include "desc.h"
 #include "processor.h"
+#include "smp.h"
 #include <setjmp.h>
 #include "apic-defs.h"
 
@@ -155,11 +156,10 @@ void unhandled_exception(struct ex_regs *regs, bool cpu)
 static void check_exception_table(struct ex_regs *regs)
 {
 	struct ex_record *ex;
-	unsigned ex_val;
 
-	ex_val = regs->vector | (regs->error_code << 16) |
-		(((regs->rflags >> 16) & 1) << 8);
-	asm("mov %0, %%gs:4" : : "r"(ex_val));
+	this_cpu_write_exception_vector(regs->vector);
+	this_cpu_write_exception_rflags_rf((regs->rflags >> 16) & 1);
+	this_cpu_write_exception_error_code(regs->error_code);
 
 	for (ex = &exception_table_start; ex != &exception_table_end; ++ex) {
 		if (ex->rip == regs->rip) {
@@ -296,10 +296,7 @@ void setup_idt(void)
 
 unsigned exception_vector(void)
 {
-	unsigned char vector;
-
-	asm volatile("movb %%gs:4, %0" : "=q"(vector));
-	return vector;
+	return this_cpu_read_exception_vector();
 }
 
 int write_cr4_checking(unsigned long val)
@@ -312,18 +309,12 @@ int write_cr4_checking(unsigned long val)
 
 unsigned exception_error_code(void)
 {
-	unsigned short error_code;
-
-	asm volatile("mov %%gs:6, %0" : "=r"(error_code));
-	return error_code;
+	return this_cpu_read_exception_error_code();
 }
 
 bool exception_rflags_rf(void)
 {
-	unsigned char rf_flag;
-
-	asm volatile("movb %%gs:5, %b0" : "=q"(rf_flag));
-	return rf_flag & 1;
+	return this_cpu_read_exception_rflags_rf() & 1;
 }
 
 static char intr_alt_stack[4096];
diff --git a/lib/x86/smp.c b/lib/x86/smp.c
index b24675fd..683b25d1 100644
--- a/lib/x86/smp.c
+++ b/lib/x86/smp.c
@@ -54,15 +54,12 @@ int cpu_count(void)
 
 int smp_id(void)
 {
-	unsigned id;
-
-	asm ("mov %%gs:0, %0" : "=r"(id));
-	return id;
+	return this_cpu_read_smp_id();
 }
 
 static void setup_smp_id(void *data)
 {
-	asm ("mov %0, %%gs:0" : : "r"(apic_id()) : "memory");
+	this_cpu_write_smp_id(apic_id());
 }
 
 static void __on_cpu(int cpu, void (*function)(void *data), void *data, int wait)
diff --git a/lib/x86/smp.h b/lib/x86/smp.h
index f74845e6..eb037a46 100644
--- a/lib/x86/smp.h
+++ b/lib/x86/smp.h
@@ -1,7 +1,72 @@
 #ifndef _X86_SMP_H_
 #define _X86_SMP_H_
+
+#include <stddef.h>
 #include <asm/spinlock.h>
 
+/* Offsets into the per-cpu page. */
+struct percpu_data {
+	uint32_t  smp_id;
+	union {
+		struct {
+			uint8_t   exception_vector;
+			uint8_t   exception_rflags_rf;
+			uint16_t  exception_error_code;
+		};
+		uint32_t exception_data;
+	};
+};
+
+#define typeof_percpu(name) typeof(((struct percpu_data *)0)->name)
+#define offsetof_percpu(name) offsetof(struct percpu_data, name)
+
+#define BUILD_PERCPU_OP(name)								\
+static inline typeof_percpu(name) this_cpu_read_##name(void)				\
+{											\
+	typeof_percpu(name) val;							\
+											\
+	switch (sizeof(val)) {								\
+	case 1:										\
+		asm("movb %%gs:%c1, %0" : "=q" (val) : "i" (offsetof_percpu(name)));	\
+		break;									\
+	case 2:										\
+		asm("movw %%gs:%c1, %0" : "=r" (val) : "i" (offsetof_percpu(name)));	\
+		break;									\
+	case 4:										\
+		asm("movl %%gs:%c1, %0" : "=r" (val) : "i" (offsetof_percpu(name)));	\
+		break;									\
+	case 8:										\
+		asm("movq %%gs:%c1, %0" : "=r" (val) : "i" (offsetof_percpu(name)));	\
+		break;									\
+	default:									\
+		asm volatile("ud2");							\
+	}										\
+	return val;									\
+}											\
+static inline void this_cpu_write_##name(typeof_percpu(name) val)			\
+{											\
+	switch (sizeof(val)) {								\
+	case 1:										\
+		asm("movb %0, %%gs:%c1" :: "q" (val), "i" (offsetof_percpu(name)));	\
+		break;									\
+	case 2:										\
+		asm("movw %0, %%gs:%c1" :: "r" (val), "i" (offsetof_percpu(name)));	\
+		break;									\
+	case 4:										\
+		asm("movl %0, %%gs:%c1" :: "r" (val), "i" (offsetof_percpu(name)));	\
+		break;									\
+	case 8:										\
+		asm("movq %0, %%gs:%c1" :: "r" (val), "i" (offsetof_percpu(name)));	\
+		break;									\
+	default:									\
+		asm volatile("ud2");							\
+	}										\
+}
+BUILD_PERCPU_OP(smp_id);
+BUILD_PERCPU_OP(exception_vector);
+BUILD_PERCPU_OP(exception_rflags_rf);
+BUILD_PERCPU_OP(exception_error_code);
+
 void smp_init(void);
 
 int cpu_count(void);
-- 
2.35.0.rc0.227.g00780c9af4-goog

