[PATCH 5.4 11/18] x86: xen: kvm: Gather the definition of emulate prefixes

Greg Kroah-Hartman
2022-05-13T14:29:51Z

From: Masami Hiramatsu <mhiramat@kernel.org>

commit b3dc0695fa40c3b280230fb6fb7fb7a94ce28bf4 upstream.

Gather the emulate prefixes, which forcibly make the following
instruction emulated on virtualization, in one place.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juergen Gross <jgross@suse.com>
Cc: x86@kernel.org
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: xen-devel@lists.xenproject.org
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/156777563917.25081.7286628561790289995.stgit@devnote2
Signed-off-by: Maximilian Heyne <mheyne@amazon.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/include/asm/emulate_prefix.h | 14 ++++++++++++++
arch/x86/include/asm/xen/interface.h | 11 ++++-------
arch/x86/kvm/x86.c | 4 +++-
3 files changed, 21 insertions(+), 8 deletions(-)
create mode 100644 arch/x86/include/asm/emulate_prefix.h

--- /dev/null
+++ b/arch/x86/include/asm/emulate_prefix.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_EMULATE_PREFIX_H
+#define _ASM_X86_EMULATE_PREFIX_H
+
+/*
+ * Virt escape sequences to trigger instruction emulation;
+ * ideally these would decode to 'whole' instruction and not destroy
+ * the instruction stream; sadly this is not true for the 'kvm' one :/
+ */
+
+#define __XEN_EMULATE_PREFIX 0x0f,0x0b,0x78,0x65,0x6e /* ud2 ; .ascii "xen" */
+#define __KVM_EMULATE_PREFIX 0x0f,0x0b,0x6b,0x76,0x6d /* ud2 ; .ascii "kvm" */
+
+#endif
--- a/arch/x86/include/asm/xen/interface.h
+++ b/arch/x86/include/asm/xen/interface.h
@@ -379,12 +379,9 @@ struct xen_pmu_arch {
* Prefix forces emulation of some non-trapping instructions.
* Currently only CPUID.
*/
-#ifdef __ASSEMBLY__
-#define XEN_EMULATE_PREFIX .byte 0x0f,0x0b,0x78,0x65,0x6e ;
-#define XEN_CPUID XEN_EMULATE_PREFIX cpuid
-#else
-#define XEN_EMULATE_PREFIX ".byte 0x0f,0x0b,0x78,0x65,0x6e ; "
-#define XEN_CPUID XEN_EMULATE_PREFIX "cpuid"
-#endif
+#include <asm/emulate_prefix.h>
+
+#define XEN_EMULATE_PREFIX __ASM_FORM(.byte __XEN_EMULATE_PREFIX ;)
+#define XEN_CPUID XEN_EMULATE_PREFIX __ASM_FORM(cpuid)

#endif /* _ASM_X86_XEN_INTERFACE_H */
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -68,6 +68,7 @@
#include <asm/mshyperv.h>
#include <asm/hypervisor.h>
#include <asm/intel_pt.h>
+#include <asm/emulate_prefix.h>
#include <clocksource/hyperv_timer.h>

#define CREATE_TRACE_POINTS
@@ -5583,6 +5584,7 @@ EXPORT_SYMBOL_GPL(kvm_write_guest_virt_s

int handle_ud(struct kvm_vcpu *vcpu)
{
+ static const char kvm_emulate_prefix[] = { __KVM_EMULATE_PREFIX };
int emul_type = EMULTYPE_TRAP_UD;
char sig[5]; /* ud2; .ascii "kvm" */
struct x86_exception e;
@@ -5590,7 +5592,7 @@ int handle_ud(struct kvm_vcpu *vcpu)
if (force_emulation_prefix &&
kvm_read_guest_virt(vcpu, kvm_get_linear_rip(vcpu),
sig, sizeof(sig), &e) == 0 &&
- memcmp(sig, "\xf\xbkvm", sizeof(sig)) == 0) {
+ memcmp(sig, kvm_emulate_prefix, sizeof(sig)) == 0) {
kvm_rip_write(vcpu, kvm_rip_read(vcpu) + sizeof(sig));
emul_type = EMULTYPE_TRAP_UD_FORCED;
}