summaryrefslogtreecommitdiff
path: root/arch/x86/include/asm/kvm_para.h
diff options
context:
space:
mode:
authorPaolo Bonzini <pbonzini@redhat.com>2014-09-22 15:17:48 +0400
committerPaolo Bonzini <pbonzini@redhat.com>2014-09-24 16:07:57 +0400
commitc1118b3602c2329671ad5ec8bdf8e374323d6343 (patch)
tree57dce6397f2dbf19701fa1a7671abcde453e170b /arch/x86/include/asm/kvm_para.h
parent81760dccf8d1fe5b128b58736fe3f56a566133cb (diff)
downloadlinux-c1118b3602c2329671ad5ec8bdf8e374323d6343.tar.xz
x86: kvm: use alternatives for VMCALL vs. VMMCALL if kernel text is read-only
On x86_64, kernel text mappings are mapped read-only with CONFIG_DEBUG_RODATA. In that case, KVM will fail to patch VMCALL instructions to VMMCALL as required on AMD processors. The failure mode is currently a divide-by-zero exception, which obviously is a KVM bug that has to be fixed. However, picking the right instruction between VMCALL and VMMCALL will be faster and will help if you cannot upgrade the hypervisor. Reported-by: Chris Webb <chris@arachsys.com> Tested-by: Chris Webb <chris@arachsys.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: x86@kernel.org Acked-by: Borislav Petkov <bp@suse.de> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/include/asm/kvm_para.h')
-rw-r--r--arch/x86/include/asm/kvm_para.h10
1 files changed, 8 insertions, 2 deletions
diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index c7678e43465b..e62cf897f781 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -2,6 +2,7 @@
#define _ASM_X86_KVM_PARA_H
#include <asm/processor.h>
+#include <asm/alternative.h>
#include <uapi/asm/kvm_para.h>
extern void kvmclock_init(void);
@@ -16,10 +17,15 @@ static inline bool kvm_check_and_clear_guest_paused(void)
}
#endif /* CONFIG_KVM_GUEST */
-/* This instruction is vmcall. On non-VT architectures, it will generate a
- * trap that we will then rewrite to the appropriate instruction.
+#ifdef CONFIG_DEBUG_RODATA
+#define KVM_HYPERCALL \
+ ALTERNATIVE(".byte 0x0f,0x01,0xc1", ".byte 0x0f,0x01,0xd9", X86_FEATURE_VMMCALL)
+#else
+/* On AMD processors, vmcall will generate a trap that we will
+ * then rewrite to the appropriate instruction.
*/
#define KVM_HYPERCALL ".byte 0x0f,0x01,0xc1"
+#endif
/* For KVM hypercalls, a three-byte sequence of either the vmcall or the vmmcall
* instruction. The hypervisor may replace it with something else but only the