KVM: SVM: Use asm goto to handle unexpected #UD on SVM instructions

Add svm_asm*() macros, a la the existing vmx_asm*() macros, to handle
faults on SVM instructions instead of using the generic __ex(), a.k.a.
__kvm_handle_fault_on_reboot().  Using asm goto generates slightly
better code as it eliminates the in-line JMP+CALL sequences that are
needed by __kvm_handle_fault_on_reboot() to avoid triggering BUG()
from fixup (which generates bad stack traces).

Using SVM specific macros also drops the last user of __ex() and the
the last asm linkage to kvm_spurious_fault(), and adds a helper for
VMSAVE, which may gain an addition call site in the future (as part
of optimizing the SVM context switching).

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20201231002702.2223707-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/sev.c

@@ -22,6 +22,7 @@
 
 #include "x86.h"
 #include "svm.h"
+#include "svm_ops.h"
 #include "cpuid.h"
 #include "trace.h"
 
@@ -2076,7 +2077,7 @@ void sev_es_vcpu_load(struct vcpu_svm *svm, int cpu)
 	 * of which one step is to perform a VMLOAD. Since hardware does not
 	 * perform a VMSAVE on VMRUN, the host savearea must be updated.
 	 */
-	asm volatile(__ex("vmsave %0") : : "a" (__sme_page_pa(sd->save_area)) : "memory");
+	vmsave(__sme_page_pa(sd->save_area));
 
 	/*
 	 * Certain MSRs are restored on VMEXIT, only save ones that aren't

arch/x86/kvm/svm/svm.c

@@ -41,6 +41,7 @@
 #include "trace.h"
 
 #include "svm.h"
+#include "svm_ops.h"
 
 #define __ex(x) __kvm_handle_fault_on_reboot(x)
 
@@ -248,21 +249,6 @@ u32 svm_msrpm_offset(u32 msr)
 
 #define MAX_INST_SIZE 15
 
-static inline void clgi(void)
-{
-	asm volatile (__ex("clgi"));
-}
-
-static inline void stgi(void)
-{
-	asm volatile (__ex("stgi"));
-}
-
-static inline void invlpga(unsigned long addr, u32 asid)
-{
-	asm volatile (__ex("invlpga %1, %0") : : "c"(asid), "a"(addr));
-}
-
 static int get_max_npt_level(void)
 {
 #ifdef CONFIG_X86_64

arch/x86/kvm/svm/svm_ops.h

@@ -0,0 +1,64 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __KVM_X86_SVM_OPS_H
+#define __KVM_X86_SVM_OPS_H
+
+#include <linux/compiler_types.h>
+
+#include <asm/kvm_host.h>
+
+#define svm_asm(insn, clobber...)				\
+do {								\
+	asm_volatile_goto("1: " __stringify(insn) "\n\t"	\
+			  _ASM_EXTABLE(1b, %l[fault])		\
+			  ::: clobber : fault);			\
+	return;							\
+fault:								\
+	kvm_spurious_fault();					\
+} while (0)
+
+#define svm_asm1(insn, op1, clobber...)				\
+do {								\
+	asm_volatile_goto("1: "  __stringify(insn) " %0\n\t"	\
+			  _ASM_EXTABLE(1b, %l[fault])		\
+			  :: op1 : clobber : fault);		\
+	return;							\
+fault:								\
+	kvm_spurious_fault();					\
+} while (0)
+
+#define svm_asm2(insn, op1, op2, clobber...)				\
+do {									\
+	asm_volatile_goto("1: "  __stringify(insn) " %1, %0\n\t"	\
+			  _ASM_EXTABLE(1b, %l[fault])			\
+			  :: op1, op2 : clobber : fault);		\
+	return;								\
+fault:									\
+	kvm_spurious_fault();						\
+} while (0)
+
+static inline void clgi(void)
+{
+	svm_asm(clgi);
+}
+
+static inline void stgi(void)
+{
+	svm_asm(stgi);
+}
+
+static inline void invlpga(unsigned long addr, u32 asid)
+{
+	svm_asm2(invlpga, "c"(asid), "a"(addr));
+}
+
+/*
+ * Despite being a physical address, the portion of rAX that is consumed by
+ * VMSAVE, VMLOAD, etc... is still controlled by the effective address size,
+ * hence 'unsigned long' instead of 'hpa_t'.
+ */
+static inline void vmsave(unsigned long pa)
+{
+	svm_asm1(vmsave, "a" (pa), "memory");
+}
+
+#endif /* __KVM_X86_SVM_OPS_H */