KVM: VMX: Move VMREAD cleanup to exception handler

We clean up a failed VMREAD by clearing the output register.  Do
it in the exception handler instead of unconditionally.  This is
worthwhile since there are more than a hundred call sites.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

2 files changed, 10 insertions, 4 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d2ac8e2ee897..db4b6543b830 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -830,11 +830,12 @@ enum {
 asmlinkage void kvm_spurious_fault(void);
 extern bool kvm_rebooting;
 
-#define __kvm_handle_fault_on_reboot(insn) \
+#define ____kvm_handle_fault_on_reboot(insn, cleanup_insn)      \
         "666: " insn "\n\t" \
         "668: \n\t"                           \
         ".pushsection .fixup, \"ax\" \n" \
         "667: \n\t" \
+        cleanup_insn "\n\t"                   \
         "cmpb $0, kvm_rebooting \n\t"         \
         "jne 668b \n\t"                       \
         __ASM_SIZE(push) " $666b \n\t"        \
@@ -844,6 +845,9 @@ extern bool kvm_rebooting;
         _ASM_PTR " 666b, 667b \n\t" \
         ".popsection"
 
+#define __kvm_handle_fault_on_reboot(insn)              \
+        ____kvm_handle_fault_on_reboot(insn, "")
+
 #define KVM_ARCH_WANT_MMU_NOTIFIER
 int kvm_unmap_hva(struct kvm *kvm, unsigned long hva);
 int kvm_age_hva(struct kvm *kvm, unsigned long hva);
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index d48ec60ea421..7d22d6c6734d 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -43,6 +43,8 @@
 #include "trace.h"
 
 #define __ex(x) __kvm_handle_fault_on_reboot(x)
+#define __ex_clear(x, reg) \
+        ____kvm_handle_fault_on_reboot(x, "xor " reg " , " reg)
 
 MODULE_AUTHOR("Qumranet");
 MODULE_LICENSE("GPL");
@@ -587,10 +589,10 @@ static inline void ept_sync_individual_addr(u64 eptp, gpa_t gpa)
 
 static unsigned long vmcs_readl(unsigned long field)
 {
-        unsigned long value = 0;
+        unsigned long value;
 
-        asm volatile (__ex(ASM_VMX_VMREAD_RDX_RAX)
-                      : "+a"(value) : "d"(field) : "cc");
+        asm volatile (__ex_clear(ASM_VMX_VMREAD_RDX_RAX, "%0")
+                      : "=a"(value) : "d"(field) : "cc");
         return value;
 }