@@ -203,6 +203,7 @@
#define X86_FEATURE_DECODEASSISTS (8*32+12) /* AMD Decode Assists support */
#define X86_FEATURE_PAUSEFILTER (8*32+13) /* AMD filtered pause intercept */
#define X86_FEATURE_PFTHRESHOLD (8*32+14) /* AMD pause filter threshold */
+#define X86_FEATURE_VMMCALL (8*32+15) /* Prefer vmmcall to vmcall */
/* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */
@@ -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
@@ -509,6 +509,13 @@ static void early_init_amd(struct cpuinfo_x86 *c)
}
#endif
+ /*
+ * This is only needed to tell the kernel whether to use VMCALL
+ * and VMMCALL. VMMCALL is never executed except under virt, so
+ * we can set it unconditionally.
+ */
+ set_cpu_cap(c, X86_FEATURE_VMMCALL);
+
/* F16h erratum 793, CVE-2013-6885 */
if (c->x86 == 0x16 && c->x86_model <= 0xf) {
u64 val;
This is a note to let you know that I have just added a patch titled x86: kvm: use alternatives for VMCALL vs. VMMCALL if kernel text is read-only to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue This patch is scheduled to be released in version 3.13.11-ckt12. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.13.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From f7cd7af7f04d4657e0229c07cb3e9ed9a0d7bec2 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini <pbonzini@redhat.com> Date: Mon, 22 Sep 2014 13:17:48 +0200 Subject: x86: kvm: use alternatives for VMCALL vs. VMMCALL if kernel text is read-only commit c1118b3602c2329671ad5ec8bdf8e374323d6343 upstream. 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> Signed-off-by: Chris J Arges <chris.j.arges@canonical.com> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- arch/x86/include/asm/cpufeature.h | 1 + arch/x86/include/asm/kvm_para.h | 10 ++++++++-- arch/x86/kernel/cpu/amd.c | 7 +++++++ 3 files changed, 16 insertions(+), 2 deletions(-) -- 1.9.1