linux-kernel - [RFC][PATCH 08/24] x86/entry: Add C version of SWAPGS and SWAPGS_UNSAFE

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Date:   Mon,  9 Nov 2020 15:44:09 +0100
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, dave.hansen@...ux.intel.com, luto@...nel.org,
        peterz@...radead.org, linux-kernel@...r.kernel.org,
        thomas.lendacky@....com, jroedel@...e.de
Cc:     konrad.wilk@...cle.com, jan.setjeeilers@...cle.com,
        junaids@...gle.com, oweisse@...gle.com, rppt@...ux.vnet.ibm.com,
        graf@...zon.de, mgross@...ux.intel.com, kuzuno@...il.com,
        alexandre.chartre@...cle.com
Subject: [RFC][PATCH 08/24] x86/entry: Add C version of SWAPGS and SWAPGS_UNSAFE_STACK

SWAPGS and SWAPGS_UNSAFE_STACK are assembly macros. Add C versions
of these macros (swapgs() and swapgs_unsafe_stack()).

Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
---
 arch/x86/include/asm/paravirt.h       | 15 +++++++++++++++
 arch/x86/include/asm/paravirt_types.h | 17 ++++++++++++-----
 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index d25cc6830e89..a4898130b36b 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -145,6 +145,21 @@ static inline void __write_cr4(unsigned long x)
 	PVOP_VCALL1(cpu.write_cr4, x);
 }
 
+static inline void swapgs(void)
+{
+	PVOP_VCALL0(cpu.swapgs);
+}
+
+/*
+ * If swapgs is used while the userspace stack is still current,
+ * there's no way to call a pvop.  The PV replacement *must* be
+ * inlined, or the swapgs instruction must be trapped and emulated.
+ */
+static inline void swapgs_unsafe_stack(void)
+{
+	PVOP_VCALL0_ALT(cpu.swapgs, "swapgs");
+}
+
 static inline void arch_safe_halt(void)
 {
 	PVOP_VCALL0(irq.safe_halt);
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 0fad9f61c76a..eea9acc942a3 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -532,12 +532,12 @@ int paravirt_disable_iospace(void);
 		      pre, post, ##__VA_ARGS__)
 
 
-#define ____PVOP_VCALL(op, clbr, call_clbr, extra_clbr, pre, post, ...)	\
+#define ____PVOP_VCALL(op, insn, clbr, call_clbr, extra_clbr, pre, post, ...) \
 	({								\
 		PVOP_VCALL_ARGS;					\
 		PVOP_TEST_NULL(op);					\
 		asm volatile(pre					\
-			     paravirt_alt(PARAVIRT_CALL)		\
+			     paravirt_alt(insn)				\
 			     post					\
 			     : call_clbr, ASM_CALL_CONSTRAINT		\
 			     : paravirt_type(op),			\
@@ -547,12 +547,17 @@ int paravirt_disable_iospace(void);
 	})
 
 #define __PVOP_VCALL(op, pre, post, ...)				\
-	____PVOP_VCALL(op, CLBR_ANY, PVOP_VCALL_CLOBBERS,		\
-		       VEXTRA_CLOBBERS,					\
+	____PVOP_VCALL(op, PARAVIRT_CALL, CLBR_ANY,			\
+		       PVOP_VCALL_CLOBBERS, VEXTRA_CLOBBERS,		\
 		       pre, post, ##__VA_ARGS__)
 
+#define __PVOP_VCALL_ALT(op, insn)					\
+	____PVOP_VCALL(op, insn, CLBR_ANY,				\
+		       PVOP_VCALL_CLOBBERS, VEXTRA_CLOBBERS,		\
+		       "", "")
+
 #define __PVOP_VCALLEESAVE(op, pre, post, ...)				\
-	____PVOP_VCALL(op.func, CLBR_RET_REG,				\
+	____PVOP_VCALL(op.func, PARAVIRT_CALL, CLBR_RET_REG,		\
 		      PVOP_VCALLEE_CLOBBERS, ,				\
 		      pre, post, ##__VA_ARGS__)
 
@@ -562,6 +567,8 @@ int paravirt_disable_iospace(void);
 	__PVOP_CALL(rettype, op, "", "")
 #define PVOP_VCALL0(op)							\
 	__PVOP_VCALL(op, "", "")
+#define PVOP_VCALL0_ALT(op, insn)					\
+	__PVOP_VCALL_ALT(op, insn)
 
 #define PVOP_CALLEE0(rettype, op)					\
 	__PVOP_CALLEESAVE(rettype, op, "", "")
-- 
2.18.4